Commodore 64 computer Programmers reference guide

The Commodore 64 is a home computer that provides the user with a variety of graphics modes, including a 40 column by 25 line text display, a 320 by 200 dot high resolution display, and SPRITES, small movable objects which make writing games simple. This manual describes the graphics capabilities of the Commodore 64 and provides a guide for programmers working with its graphics features.

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GRAPHICS OVERVIEW

All of the graphics abilities of the Commodore 64 come from the 6567

Video Interface Chip (also known as the VIC-II chip). This chip gives a variety of graphics modes, including a 40 column by 25 line text display, a 320 by 200 dot high resolution display, and SPRITES, small movable objects which make writing games simple. And if this weren't enough, many of the graphics modes can be mixed on the same screen.

It is possible, for example, to define the top half of the screen to be in high resolution mode, while the bottom half is in text mode. And SPRITESwill combine with anything!

A) CHARACTER DISPLAYMODES

1) Standard Character Mode

a) ROM characters b) RAM programmable characters

2) Multi-Color Character Mode

a) ROM characters b) RAM programmable characters

3) Extended Background Color Mode

a) ROM characters b) RAM programmable characters

B) BIT MAP MODES

1) Standard Bit Map Mode

2) Multi-Color Bit Map Mode

C) SPRITES

100

1) Standard Sprites

2) Multi-Color Sprites

PROGRAMMING GRAPHICS

GRAPHICS LOCATIONS

Some general information first. There are 1000 possible locations on the Commodore 64 screen.

Normally, the screen starts at location 1024

($0400 in HEXadecimal notation) and goes to location 2023. Each of these locations is 8 bits wide. This means that it can hold any integer number from 0 to 255. Connected with screen memory is a group of

1000 locations called COLOR MEMORY or COLOR RAM. These start at location 55296 ($D800 in HEX) and go up to 56295. Each of the color

RAM locations is 4 bits wide, which means that it can hold any integer number from 0 to 15. Since there are 16 possible colors that the Commodore 64 can use, this works out well.

In addition, there are 256 different characters that can be displayed at any time. For normal screen display, each of the 1000 locations in screen memory contains a code number which tells the VIC-II chip which character to display at that screen location.

The various graphics modes are selected by the 47 CONTROL registers in the VIC-II chip. Many of the graphics functions can be controlled by POKEing the correct value into one of the registers. The VIC-II dhip is located starting at 53248 ($DOOOin HEX)through 53294 ($D02E in HEX).

VIDEO BANK SELECTION

The VIC-II chip can access ("see") 16K of memory at a time. Since there is 64K of memory in the Commodore 64, you want to be able to have the VIC-II chip see all of it. There is a way. There are 4 possible

BANKS (or sections) of 16K of memory. All that is needed is some means of controlling which 16K bank the VIC-II chip looks at. In that way, the

chip can "see" the entire 64K of memory. The BANK

SELECT

bits that

allow you access to all the different sections of memory are located in the 6526 COMPLEX INTERFACEADAPTERCHIP #2 (CIA #2). The POKE and PEEK BASIC statements (or their machine language versions) are used to select a bank by controlling bits 0 and 1 of PORT A of CIA#2

(location 56576 (or $DDOOHEX». These 2 bits must be set to outputs by setting bits 0 and 1 of location 56578 ($DD02.HEX) to change banks. The following example shows this:

POKE 56578,PEEK(56578)OR 3 :REM MAKE SURE BITS 0 AND 1 ARE

SET TO OUTPUTS

POKE 56576,(PEEK(56576)AND 252)OR A:REM CHANGE BANKS

"A" should have one of the following values:

PROGRAMMING GRAPHICS 101

VALUE BITS BANK

STARTING

OF A LOCATION

49152

32768

16384

VIC-II CHIP

RANGE

($COOO-$FFFF)*

($8000-$BFFF)

($4000$7FFF)*

($0000-$3FFF) (DEFAULT VALUE)

This 16K bank concept is part of everything that the VIC-II chip does.

You should always be aware of which bank the VIC-II chip is pointing at, since this will affect where character data patterns come from, where the screen is, where sprites come from, etc. When you turn on the power of your Commodore 64, bits 0 and 1 of location 56576 are automatically set to BANK 0 ($0000-$3FFF) for all display information.

.NOTE: The Commodore 64 character set is not available to the VIC-II chip in BANKS

1 and 3. (See character memory section.)

SCREEN MEMORY

The location of screen memory can be changed easily by a POKE to control register 53272 ($DOI8 HEX). However, this register is also used to control which character set is used, so be careful to avoid disturbing that part of the control register.

The UPPER 4 bits control the location of screen memory.

To move the screen, the following statement should be used:

POKE53272,(PEEK(53272)AND15)ORA

102 PROGRAMMING GRAPHICS

Where" A" has one of the following values:

112

128

144

160

176

192

208

224

240

BITS

OOOOXXXX

0001 XXXX

0010XXXX

0011XXXX

0100XXXX

0101XXXX

0110XXXX

0111XXXX

1000XXXX

1001XXXX

1010XXXX

1011XXXX

1100XXXX

1101XXXX

1110XXXX

1111 XXXX

DECIMAL

LOCATION*

HEX

1024

2048

3072

4096

5120

6144

7168

8192

9216

10240

11264

12288

13312

14336

15360

$0000

$0400

(DEFAULT)

$0800

$OCOO

$1000

$1400

$1800

$lCOO

$2000

$2400

$2800

$2COO

$3000

$3400

$3800

$3COO.

'Remember that the BANK ADDRESS of the VIC-II chip must be added in.

You must also tell the KERNAL'Sscreen editor where the screen is as follows: POKE

648, page (where page = address/256, e.g., 1024/256= 4, so POKE 648,4).

COLOR MEMORY

Color memory can NOT move. It is always located at locations

55296

($D800)

through

56295 ($DBE7).

Screen memory (the 1000 locations

starting at 1024) and color memory are used differently in the different graphics modes.

A picture created in one mode will often look completely different when displayed in another graphics mode.

CHARACTER MEMORY

Exactly where the VIC-II gets it character information is important to graphic programming.

Normally, the chip gets the shapes of the characters you want to be displayed from the CHARACTERGENERATOR

ROM. In this chip are stored the patterns which make up the various letters, numbers, punctuation symbols, and the other things that you see

PROGRAMMING GRAPHICS 103

on the keyboard.

One of the features of the Commodore 64 is the ability to use patterns located in RAM memory.

These RAM patterns are created by you, and that means that you can have an almost infinite set of symbols for" games, business applications, etc.

A normal character set contains 256 characters in which each c.haracter is defined by 8 bytes of data.

Since each character takes up 8 bytes this means that a full character set is 256*8=2K bytes of memory.

Since the VIC-II chip looks at 16K of memory at a time, there are 8 possible locations for a complete character set. Naturally, you are free to use less than a full character set. However, it must still start at one of the 8 possible starting locations.

The location of character memory is controlled by 3 bits of the VIC-II control register located at 53272 ($DOI8 in HEX notation). Bits 3,2, and

1 control where the characters' set is located in 2K blocks. Bit 0 is ignored.

Remember that this is the same register that deterrt.ines

where screen memory is located so avoid disturbing the screen memory bits. To change the location of character me{T1ory,the following BASIC statement can be used:

POKE 53272,(PEEK(53272)AND240)OR A

Where A is one of the following values:

BITS

LOCATION OF CHARACTER MEMORY*

VALUE

I of A

DECIMAL HEX

XXXXOOOX

2 XXXXOOIX

4 XXXXOI0X

6 XXXXOIIX

2048

4096

6144

$0000-$07FF

$0800-$OFFF

$1000-$17FF

ROM IMAGE in BANK o & 2 (default)

$1800-$1 FFF ROM IMAGE in BANK

0&2

XXXX 1 OOX

8192

$2000-$27FF

10 XXXXI0IX 10240

$2800-$2FFF

12 XXXXII0X 12288

$3000-$37FF

XXXXIIIX

14336 $3800-$3FFF

'Remember to add in the BANKaddress.

104 PROGRAMMING GRAPHICS

The ROM IMAGE in the above table refers to the character generator

ROM. It also appears in place of RAM at the above locations in bank

O. It

appears in the corresponding RAM at locations

36864-40959

($9000-$9FFF) in bank 2. Since the VIC-II chip can only access 16K of memory at a time, the ROM character patterns appear in the 16K block of memory the VIC-II chip looks at. Therefore, the system was designed to make the VIC-II chip think that the ROM characters are at 4096-8191

($1000-$1

FFF) when your data is in bank 0, and 36864-40959

($9000-$9FFF) when your data is in bank 2, even though the character

ROM is actually at location 53248-57343 ($DOOO-$DFFF). This imaging only applies to character data as seen by the VIC-II chip.

It can be used for programs, other data, etc., just like any other RAM memory.

NOTE:

If these ROM images get in the way of your own graphics, then set the BANK

SELECT BITS to one of the BANKS without the images (BANKS 1 or 3). The ROM patterns won't be there.

The location and contents of the character set in ROM are as follows:

ADDRESS

BLOCK DECIMAL

HEX

53248

53760

54272

54784

55296

55808

56320

56832

DOOO- D1FF

D200- D3FF

D400- D5FF

VIC-II

IMAGE

100011FF

1200-13FF

1400-15FF

Upper

Graphics

CONTENTS case

Reversed characters

D600- D7FF 1600- 17FF Reversed characters characters characters upper case graphics

D800- D9FF 1800- 19FF Lower case characters

DAOO- DBFF 1AOO- 1BFF

Upper case & graphics characters

DCOO- DDFF 1COO- 1DFF Reversed lower case characters

DEOO-DFFF

1EOO- 1FFF Reversed upper case & graphics characters

Sharp-eyed readers will have just noticed something.

The locations occupied by the character ROM are the same as the ones occupied by the VIC-II chip control registers.

This is possible because they don't occupy the same locations at the same time. When the VIC-II chip needs to

PROGRAMMING 105

access character data the ROM is switched in. It becomes an image in the 16K bank of memory that the VIC-II chip is looking at. Otherwise, the area is occupied by the I/O control registers, and the character ROM is only available to the VIC-II chip.

However, you may need to get to the character ROM if you are going to use programmable characters and want to copy some of the character ROM for some of your character definitions. In this case you must switch out the I/O register, switch in the character ROM, and do your copying. When you're finished, you must switch the I/O registers back in again.

During the copying process (when I/O is switched out) no interrupts can be allowed to take place. This is because the I/O registers are needed to service the interrupts.

If you forget and perform an interrupt, really strange things happen.

The keyboard should not be read during the copying process.

To turn off the keyboard and other normal interrupts that occur with your Commodore 64, the following POKE should be used:

POKE 56334,PEEK(56334)AND254

(TURNS INTERRUPTS OFF)

After you are finished getting characters from the character ROM, and are ready to continue with your program, you must turn the keyboard scan back on by the following POKE:

POKE 56334,PEEK(56334)ORI

(TURNS INTERRUPTS ON)

The following POKE will switch out I/O and switch the CHARACTER

ROM in:

POKE l,PEEK(1)AND251

The character ROM is now in the locations from 53248-57343 ($DOOO-

$DFFF).

To switch I/O back into $DOOOfor normal operation use the following

POKE:

106

POKE l,PEEK(l)OR 4

PROGRAMMING GRAPHICS

STANDARD CHARACTER MODE

Standard character mode is the mode the Commodore 64 is in when you first turn it on. It is the mode you will generally program in.

Characters can be taken from ROM or from RAM, but normally they are taken from ROM. When you want special graphics characters for a program, all you have to do is define the new character shapes in RAM, and tell the VIC-II chip to get its character information from there instead of the character ROM. This is covered in more detail in the next section.

In order to display characters on the screen in color, the VIC-II chip accesses the screen memory to determine the character code for that location on the screen. At the same time, it accesses the color memory to determine what color you want for the character displayed.

The character code is translated by the VIC-II into the starting address of the

8-byte block holding your character pattern.

The 8-byte block is located in character memory.

The translation isn't too complicated, but a number of items are combined to generate the desired address.

First the character code you use to POKE screen memory is multiplied by 8. Next add the start of character memory (see CHARACTERMEMORYsection). Then the Bank Select

Bits are taken into account by adding in the base address (see VIDEO

BANK SELECTIONsection). Below is a simple formula to illustrate what happens:

CHARACTER ADDRESS

SCREEN CODE*8+(CHARACTER

S ET* 2048) + (BAN K* 16384)

CHARACTER DEFINITIONS

Each character is formed in an 8 by 8 grid of dots, where each dot may be either on or off. The Commodore 64 character images are stored in the Character Generator ROM chip. The characters are stored as a set of 8 bytes for each character, with each byte representing the dot pattern of a row in the character, and each bit representing a dot.

A zero bit means that dot is off, and a one bit means the dot is on.

The character memory in ROM begins at location 53248 (when the I/O is switched off). The first 8 bytes from location 53248 ($DOOO)to 53255

($D007) contain the pattern for the @ sign, which has a character code value of zero in the screen memory.

The next 8 bytes, from location

PROGRAMMING 107

53256 ($D008) letter A.

to 53263 ($DOOF),

IMAGE

****

** **

******

** **

** ** contain the information

BINARY PEEK

00011000 24

00111100 60

011 0011 0

102

01111110 126

011 0011 0

102

01100110

102

011 0011 0

102

00000000 0 for forming the

Each complete bytes per character character and 256 set takes characters.

up 2K

Since

(2048 there bits) of are two memory, character

8 sets, one for upper case and graphics lower tions.

case, the character generator ROM and the other with upper takes up a total of 4K and loca-

PROGRAMMABLE CHARACTERS

Since the characters are stored in ROM, it would seem that there is no way to change them for customizing characters. However, the memory location grammable memory.

that

By tells the VIC-II chip where register which can be changed changing the character to find memory the characters to point to many pointer to is a prosections point to RAM, of the character set may be programmed for any need.

If you want your character set to be located in RAM, there are a few

VERY

IMPORTANT

things to take into account when you decide to actually program your own charadter sets.

In addition, there are two other important points you must know to create your own special characters:

108

1) Itis an allor nothing pr0gess. Generally, ifyou use your own character set by telling the Vlt-II chip to get the character information from the area you have prepared in RAM, the standard Commodore 64 characters are unavailable to you.

To solve this, you must copy any letters,numbers, or standard Commodore 64 graphics you intend to use intoyour own character memory in RAM.

You can pick and choose, take only the ones you want, and don't even have to keep them in order!

PROGRAMMING GRAPHICS

2) Your character set takes memory space away from your BASIC program.

Of course, with 38K available for a BASIC program, most applications won't have problems.

WARNING: You must be careful to protect the character set from being overwritten by your BASIC program, which also uses the RAM.

There are two locations in the Commodore 64 to start your character set that should NOT be used with BASIC: location 0 and location

2048. The first should not be used because the system stores important data on page O. The second can't be used because that is where your

BASIC program starts! However, there are 6 other starting positions for your custom character set.

The best place to put your character set for use with BASIC while experimenting is beginning at 12288 ($3000 in HEX). This is done by

POKEing the low 4 bits of location 53272 with 12. Try the POKE now, like this:

POKE 53272,(PEEK(53272)AND240)+ 12

Immediately, all the letters on the screen turn to garbage, This is because there are no characters set up at location 12288 right now.

. .

only random bytes. Set the Commodore 64 back to normal by hitting the .:mlr~'111111 key.

Now let's begin creating graphics characters.

To protect your character set from BASIC, you should reduce the amount of memory BASIC thinks it has.

The amount of memory in your computer stays the same.

. . it's just that you've told BASIC not to use some of it. Type:

PRINT FRE(O)-(SGN(FRE(O»<O)*65535

The number displayed is the amount of memory space left unused.

Now type the following:

POKE 52,48:POKE56,48:CLR

Now type:

PRINT FRE(O)-(SGN(FRE(O»<0)*65535

PROGRAMMING 109

See the change?

BASIC now thinks it has less memory to work with. The memory you just claimed from BASIC is where you are going to put your character set, safe from actions of BASIC.

The next step is to put your characters into RAM. When you begin, there is random data beginning at 12288 ($3000 HEX). You must put character patterns in RAM (in the same style as the ones in ROM) for the

VIC-II chip to use.

The following program moves 64 characters from ROM to your character set RAM:

5 PRINTCHR$(142)

UPPER CASE

:REM SWITCH TO

10 POKE52,48:POKE56,48:CLR

FOR CHARACTERS

:REM RESERVE MEMORY

20 POKE56334, PEEK (56334) At.m254 :REt1 TURt.~OFF

KEYSCAN INTERRUPTTIMER

30 POKE1,PEEK(1)AND251 :REM SWITCH IN

CHARACTER

4121 FOR I =0T0511 :POKE I + 12288., PEEK ( 1+53248)

50 POKE1,PEEK(1)OR4

: t~E:":T

:REM SWITCH IN I/O

60 POKE56334,PEEK(56334)OR1

KEYSCAN INTERRUPT TIMER

70 Et~D

:REM RESTART

Now POKE location

53272 with (PEEK(53272)AND240)+ 12. Nothing happens, right? Well, almost nothing. The Commodore 64 is now getting it's character information from your RAM, instead of from ROM. But since we copied the characters from ROM exactly, no difference can be seen.

. . . yet.

You can easily change the characters now. Clear the screen and type an @ sign. Move the cursor down a couple of lines, then type:

FOR I = 12288 TO 12288+7:POKE I, 255

PEEK(I): NEXT

You just created a reversed @ sign!

110

TIP: Reverse.d characters are just characters with their bit patterns in character memory

reversed.

Now move the cursor up to the program again and hit

...

again to re-reverse the character (bring it back to. normal). By looking at the table of screen display codes, you can figure out where in RAM each character is. Just remember that each character takes eight memory locations to store. Here's a few examples just to get you started:

PROGRAMMING GRAPHICS

CHARACTER DISPLAYCODE CURRENTSTARTINGLOCATION IN RAM

12288

12296

12552

12784

Remember that we only took the first 64 characters.

Something else will have to be done if you want one of the other characters.

What if you wanted character number 154, a reversed Z? Well, you could make it yourself, by reversing a Z, or you could copy the set of reversed characters from the ROM, or just take the one. character you want from ROM and replace one of the characters you have in RAM that you don't need.

Suppose you decide that you won't need the> sign. Let's replace the

> sign with the reversed Z. Type this:

FOR 1=0 TO 7: POKE 12784 + I, 255-PEEK(I+12496): NEXT

Now type a > sign.

It comes up as a reversed Z. No matter how many times you type the>, it comes out as a reversed

Z. (This change is really an illusion. Though the> sign looks like a reversed Z, it still acts like a >in a program.

Try something that needs a > sign.

It will still work fine, only it will look strange.)

A quick

review: You can now copy characters from ROM into RAM.

You can even pick and choose only the ones you want.

There's only one step left in programmable characters (the best step!)

. . .

making your own characters.

Remember how characters are stored in ROM? Each character is

stored as a group of eight bytes.

The bit

patterns of the bytes directly

control the character.

If you arrange 8 bytes, one on top of another, and write out each byte as eight binary digits, it forms an eight by eight matrix, looking like the characters.

When a bit is a one, there is a dot at that location. When a bit is a zero, there is a space at that location.

When creating your own

characters,

you set up the same kind of table

In memory. Type

NEWand then type this program:

10 FOR I = 12448 TO 12455

: READ A: POKE I,A: NEXT

20 DATA 60, 66, 165, 129, 165, 153, 66, 60

PROGRAMMING GRAPHICS

111

Now type RUN. The program will replace the letter T with a smile face character.

Type a few 1's to see the face.

Each of the numbers in the

DATA statement in line 20 is a row in the smile face character.

The matrix for the face looks like this:

65432

1 0

BINARY DECIMAL

ROW 0

ROW 7

* * * *

* *

* * * *

001111 00

01000010

10100101

10000001

10100101

10011001

01000010

001111:00

165

129

165

153

6 5

2 1 o

7 o

Figure 3-1. Programmable Character Worksheet.

112 PROGRAMMING GRAPHICS

The Programmable Character Worksheet (Figure 3-1) will help you design your own characters.

There is an 8 by 8 matrix on the sheet, with row numbers, and numbers at the top of each column. (If you view each row as a binary word, the numbers are the value of that bit position.

Each is a power of 2. The leftmost bit is equal to 128 or 2 to the 7th power, the next is equal to 64 or 2 to the 6th, and so on, until you reach the rightmost bit (bit 0) which is equal to 1 or 2 to the 0 power.)

Place an X on the matrix at every location where you want a dot to be in your character.

When your character is ready you can create the

DATAstatement for your character.

Begin with the first row. Wherever you placed an X, take the number at the top of the column (the power-of-2 number, as explained above) and write it down. When you have the numbers for every column of the first row, add them together.

Write this number down, next to the row.

This is the number that you will put into the DATAstatement to draw this row.

Do the same thing with all of the other rows (I -7).

When you are finished you should have 8 numbers between 0 and 255. If any of your numbers are not within range, recheck your addition. The numbers must be in this range to be correct! If you have less than 8 numbers, you missed a row. It's OK if some are o. The 0 rows are just as important as the other numbers.

Replace the numbers in the DATAstatement in line 20 with the numbers you just calculated, and RUN the program.

Then type a T. Every time you type it, you'll see your own character!

If you don't like the way the character turned out, just change the numbers in the DATAstatement and re-RUN the program until you are happy with your character.

That's all there is to it!

HINT: For best results, always make any vertical lines in your characters at least 2 dots (bits) wide.

This helps prevent CHROMA noise (color distortion) on your characters when they ore displayed on a TV screen.

PROGRAMMING GRAPHICS 113

Here characters: is an example of a program using standard programmable

10 REM* EXAMPLE1 *

2121REM CREATING PROGRAMMABLE CHARACTERS

31 POKE56334.PEEK(56334)AND254:POKE1,PEEK(I)AND251:

REM TURN OFF KB AND 110

35 FORI=0T063:REM

FROt1 ROM

36 FORJ=0T07:REM

CHARACTER RANGE TO BE COPIED

COPY ALL 8 BYTES PER CHARACTER

37 POKEI2288+I~8+J,PEEK(53248+I*8+J);REM COpy

B'r'TE

38 NEXTJ:NEXTI:REM GOTO NEXT BYTE OR CHARACTER

39 POKE1,PEEK(I)OR4:POKE56334,PEEK(56334)OR1;REM

TURN ON 1/0 AND KB

40 POKE532?2,(PEEK(53272)AND240)+12:REM

POINTER TO MEM. 12288

SET CHAR

6121FORCHAR=60TOG3:REM PROGRAM CHARACTERS 6121THRU 63

8121FORBYTE=I21TO?;REM DO ALL 8 BYTES OF A CHARACTER

10121READ NUMBER:REM READ IN 1/8TH OF CHARACTER DATA

12121POKE 12288+ (S*-CHAR)+B'r'TE.. NUMBER: REM STORE THE

DATA I t.~ t1EMOR'T'

14121 NEXTBYTE:NEXTCHAR;REM ALSO COULD BE NEXT BYTE,

CHAR

15121 PRINTCHR$(147)TAB(255)CHR$(60);

155 PRINTCHR$(61)TAB(55)CHR$(62)CHR$(63)

160 REM LINE 150 PUTS THE NEWLY DEFINED CHARACTERS

Ot~ THE SCREEN

170 GETA$:REM WAIT FOR USER TO PRESS A KEY

TR'T' AGAIN!

19121POKE53272,21:REM

21210 DATA4.G,?,5,7,?3,3:REM

21121 DATA 32,96,224,

FOR CHARACTER 61

22121 DATA?,7,7.31,31,95,

CHARACTER 62

RETURN TO NORMAL CHARACTERS

DATA FOR CHARACTER 6121

16121,224,224,192,192;REM

143,127:REM DATA FOR

DATA

23121 DATA 224,224.224,248,248,248,24121,224:REM

FOR CHARACTER 63

240 END

DATA

114

PROGRAMMING GRAPHICS

MULTI-COLOR MODE GRAPHICS

Standard high-resolution graphics give you control of very small dots on the screen.

Each dot in character memory can have 2 possible values, 1 for on and 0 for off. When a dot is off, the color of the screen is used in the space reserved for that dot. If the dot is on, the dot is colored with the character color you have chosen for that screen position. When you're using standard high-resolution graphics, all the dots within each 8 X 8 character can either have background color or foreground color. In some ways this limits the color resolution within that space.

For example, problems may occur when two different colored lines cross.

Multi-color mode gives you a solution to this problem.

Each dot in multi-color mode can be one of 4 colors: screen color (background color register #0), the color in background register #1, the color in background color register #2, or character color. The only sacrifice is in the horizontal resolution, because each multi-color mode dot is twice as wide as a high-resolution dot. This minimal loss of resolution is more than compensated for by the extra abilities of multi-color mode.

MULTI-COLOR MODE

BIT

To turn on multi-color character mode, set bit 4 of the VIC-II control register at 53270 ($D016) to a 1 by using the following POKE:

POKE 53270,PEEK(53270)OR 16

To turn off multi-color character mode, set bit 4 of location 53270 to a o by the following POKE:

POKE 53270,PEEK(53270)AND 239

Multi-color mode is set on or off for each space on the screen, so that multi-color graphics can be mixed with high-resolution (hi-res) graphics.

This is controlled by bit 3 in color memory.

Color memory begins at location 55296 ($D800 in HEX). If the number in color memory is less than 8 (0-7) the corresponding space on the video screen will be standard hi-res, in the color (0-7) you've chosen. If the number located in color memory is greater or equal to 8 (from 8 to 15), then that space will be displayed in multi-color mode.

PROGRAMMING

115

By POKEing a number into color memory, you can change the color of the character in that position on the screen. POKEing a number from 0 to

7 gives the normal character colors. POKEing a number between 8 and

15 puts the space into multi-color mode.

In other words, turning BIT 3

ON in color memory, sets MULTI-COLORMODE. Turning BIT 3 OFF in color memory, sets the normal, HIGH-RESOLUTIONmode.

Once multi-color mode is set in a space, the bits in the character determine which colors are displayed for the dots. For example, here is a picture of the letter A, and its bit pattern:

IMAGE

BIT PATTERN

00011 000

*****

00111100

** **

0110011 0

******

01111110

01100110

** **

011 00110

** **

011 0011 0

00000000

In normal or high-resolution mode, the screen color is displayed everywhere there is a 0 bit, and the character color is displayed where the bit is a 1. Multi-color mode uses the bits in pairs, like so:

IMAGE

AABB

CCCC

AABBAABB

AACCCCBB

AABBAABB

BIT PATTERN

00 01 10 00

00 11 11 00

01 10 01 10

01 11 11 10

01 1001 10

01 10 01 10

00 00 00 00

In the image area above, the spaces marked AA are drawn in the background #1 color, the spaces marked BB use the background #2 color, and the spaces marked CC use the character color. The bit pairs determine this, according to the following chart;

116 PROGRAMMING GRAPHICS

BIT PAIR

COLOR REGISTER

Background #0 color (screen color)

Background #1 color

Background #2 color

Color specified by the lower 3 bits in color memory

LOCATION

53281 ($D021)

53282 ($D022)

53283 ($D023) color RAM

NOTE: The sprite foreground color is a 10. The character foreground color is a 11.

Type NEW and then type this demonstration program: lee POKE53281,I:REM

~IHITE

SET BACKGROUND COLOR i0 TO

110 POKE53282,3:REM SET BACKGROUND COLOR il TO CYAN

1213

POKE53283,8:REM SET BACKGROUND COLOR i2 TO

ORANGE

1313 POKE5327ehPEEK (53270) OR16 : REt1 TURr~ Ot~ t'1ULTI COLOR t10DE

1413 C=13*4096+8*256:REM SET C TO POINT TO COLOR t1Et10RY

1513 PRItHCHR$(

147)

"AAAAAAAAAA"

.1613

FORL-=13T09

179 POKEC+L,8:REM USE MULTI BLACK

1813 t'~E;:n

The screen color is white, the character color is black, one color register is cyan (greenish blue), the other is orange.

You're not really putting color codes in the :space for character color, you're actually using references to the registers associated with those colors. This conserves memory, since 2 bits can be used to pick 16 colors

(background) or 8 colors (character).

This also 'makes some neat tricks possible. Simply changing one of the indirect registers will change every dot drawn in that color. Therefore everything drawn in the screen and

PROGRAMMING

117

background colors can be changed on the whole screen instantly. Here is an example of changing background color register #1:

TURN ON 10121 POKE53270.PEEK(5327e)OR16:REM

~IULTI COLOR t10DE

110 PRINTCHR$(147)CHR$(18),

12121PR I ~n" ;:t~"; : REM TYPE C= ~\ 1 FOR ORANGE OR

MULTICOLOR BLACK BACKGROUND

130 FORL=1T022: PRINTCHR$(65)

: NEXT

135 FORT=1T0500:NEXT

140 PR I ~n" =f.7~1;';~

CHA~jGE

TYPE CTRL .!\ 7 FOR BLUE COLOR

145 FORT=1T0500:NEXT

150 PRINT"8HIT A KEY"

1610 GETI'=!$:I FA$=" "THEN 160

170 X=INT(RND(1)~16)

18121

POKE 53282.X

19121GOTO 160

By using the

[I key and the COLOR keys the characters can be changed to any color, including multi-color characters.

For example, type this command:

POKE 53270,PEEK(53270)OR 16:PRINT "

";: REM LT.RED/

MULTI-COLORRED t

The word READY and anything else you type will be displayed in multi-color mode. Another color control can set you back to regular text.

118 PROGRAMMING GRAPHICS

Here characters: is an example of a program using multi-color programmable

10 REM ~ EXAMPLE 2' ~

2(1 REt1 CF.:EAT

II.m t1ULT I COLOR PROGRAt1t1ABLE CHARACTERS

31 POKE56334,PEEK(56334)AND254:POKE1,PEEKC1)AND251

35 FOP I =OT063

FRor1 F.:or1

:REt1 CHARACTER F.:ANGETO I:E COP IED

FOR,J=0TCi?:

REt1

COP'r' ALL 8 B'T'TES PEF.: CHAF.:ACTER

37 POKE 1228:::+U:::+,J.'

B'T'TE

REt1 COP',.'A

38 NEXTJ,I:REM GOTO NEXT BYTE OR CHARACTER

:39 POKE 1 , PEEK ( 1 ::00F.:4 : POKE56334,

TURN ON I/O AND KB

PEEK

(56:;;:34) OF.: 1 : R:Et1

4C1 POKE5::'=:272..

(PEEK (5:;;:272) AHD24E:1) + 12 : REM SET

CHAF.:

POINTER

TO MEM.

12288

50 POI<E53270., PEEJ<(5327121) OF.:16

51 POKE532:::! 1 .' (I : REt1 SET BACKGROUI.m

52 POKE53282,2:REM

SET BACKGROUND

COLOR

#0 TO BLACK

COLOR # 1 TO

F.:ED

53 POKE53283,7:REM

SET

BACKGROUND

COLOR #2 TO

\'ELLm..1

6121FORCHI"!R=6(1T06:;:: R:Et'1 PROGRAt'1 CHARACTEF.:S 60 THRU 63

:30 FORB'T'TE=(IT07: F.:Et1

DO ALL 8

1;:'T'TES OF A CHARf'iCTEF.:

:l00 F::EADHUt1BEF.::

120 POKEI2288+(8*CHAR)+BYTE,NUMBER:REM

DATI"!

~1 t'IEt'IOR''''

STORE THE

140 NEXTBYTE,CHAR

15121

~rDIm

PRINT"~"TAB(255)CHR$(60)CHR$(61)TAB(55)CHR$(62)CHR$(63)

160 REt'l L I t.jE 150 PUTS THE l.jEJ,1L'T'DEF

I HED CHARACTEF.:S

ON THE SCREEI'-.I

1 ;'[1 GET I,,!:$::PEr1 J,1f'iI T FOF.: USEF.: TO PF.:ESS A I<E'T'

1:3121 I FfU:=" "THEI..j 1 7(1 : REt'1 IF 1.10 KE',.'S t.JEF.:E PRESSED.,

TR'T' AOA Hj

19121 POKE53272'.,

RETIJRN

21: POI<E5:;;:27121.. PEEI«53271)AI.jIf239:

TO NORMAL CHARACTERS

200 DATAI29,37,21,29,93.85,85,85'REM

CHARACTER 6121

DATA

FOR

F.:Et1

210 DRTA66,72,84,116,117,85,85,85:REM DATA FOR

CHAF.:~1CTEF.'

220

DATA87,87,85,21,8,S,40,O:REM DATA

FOR

CHI=IF::AC"':::R 6;<:

238 DR-' fQ 13, 213..

85.. :::4., 32.. 3Z~., 40.. 0 : F.:Et'1

CHf~F.:ACTEF.: 6::"

24~:1 EI.m

DATA FOR

PROGRAMMING

119

EXTENDED BACKGROUND COLOR MODE

Extended background color mode gives you control over the background color of each individual character, as well as over the foreground color. For example, in this mode you could display a blue character with a yellow background on a white screen.

There are 4 registers available for extended background color mode.

Each of the registers can be set to any of the 16 colors.

Color memory is used to hold the foreground color in extended background mode. It is used the same as in standard character mode.

Extended character mode places a limit on the number of different characters you can display, however. When extended color mode is on, only the first 64 characters in the character ROM (or the first 64 characters in your programmable character set) can be used.

This is because two of the bits of the character code are used to select the background color. It might work something like this:

The character code (the number you would POKE.to the. screen) of the letter "A" is a 1. When extended color mode is on, if you POKEd a 1 to the screen, an "A" would appear.

If you POKEd a 65 to the screen normally, you would expect the character with character code (CHR$)

129 to appear, which is a reversed "A." This does NOT happen in extended color mode. Instead you get the same unreversed "A" as before, but on a different background color. The following chart gives the codes:

CHARACTERCODE

RANGE

BIT 7 BIT 6

0-63

64-127

128-191

192-255

BACKGROUND COLOR REGISTER

NUMBER ADDRESS

53281 ($D021)

53282 ($D022)

53283 ($D023)

53284 ($D024)

Extended color mode is turned ON by setting bit 6 of the VIC-II register to a .1 at location 53265 ($D011 in HEX). The following POKE does it:

120

POKE 53265, PEEK(53265)OR 64

PROGRAMMING GRAPHICS

Extended color mode is turned OFF by setting bit 6 of the VIC-II register to a 0 at location 53265 ($D011). The following statement will do this:

POKE 53265, PEEK(53265)AND 191

BIT MAPPED GRAPHICS

When writing games, plotting charts for business applications, or other types of programs, sooner or later you get to the point where you want high-resolution displays.

The Commodore 64 has been designed to do just that: high resolution is available through bit mapping of the screen.

Bit mapping is the method in which each possible dot (pixel) of resolution on the screen is assigned its own bit (location) in memory. If that memory bit is a one, the dot it is assigned to is on. If the bit is set to zero, the dot is off.

High-resolution graphic design has a couple of drawbacks, which is why it is not used all the time. First of all, it takes lots of memory to bit map the entire screen. This is because every pixel must have a memory bit to control it. You are going to need one bit of memory for each pixel

(or one byte for 8 pixels). Since each character is 8 by 8, and there are

40 lines with 25 characters in each line, the resolution is 320 pixels (dots) by 200 pixels for the whole screen. That gives you 64000 separate dots, each of which requires a bit in memory. In other words, 8000 bytes of memory are needed to map the whole screen.

Generally, high-resolution operations are made of many short, simple, repetitive routines. Unfortunately, this kind of thing is usually rather slow if you are trying to write high-resolution routines in BASIC. However, short, simple, repetitive routines are exactly what machine language does best. The solution is to either write your programs entirely in machine language, or call machine language, high-resolution subroutines from your BASIC program using the SYS command from BASIC.

That way you get both the ease of writing in BASIC, and the speed of machine language for graphics.

The VSP cartridge is also available to add high-resolution commands to COMMODORE 64 BASIC.

All of the examples given in this section will be in BASIC to make them clear.

Now to the technical details.

BIT MAPPING is one of the most popular graphics techniques in the computer world. It is used to create highly detailed pictures.

Basically, when the Commodore 64 goes into bit map mode, it directly displays an

PROGRAMMING GRAPHICS 121

8K section of memory on the TV screen. When in bit map mode, you can

directly control whether an individual dot on the screen is on or off.

There are two types of bit mapping available on the Commodore 64.

They are:

1) Standard (high-resolution) bit mapped mode (320-dot by 200-dot resolution)

2) Multi-color bit mapped mode (160-dot by 200-dot resolution)

Each is very similar to the character type it is named for: standard has greater resolution, but fewer color selections.

On the other hand, multicolor bit mapping trades horizontal resolution for a greater number of colors in an 8-dot by a-dot square.

STANDARD HIGH-RESOLUTION BIT MAP MODE

Standard bit map mode gives you a 320 horizontal dot by 200 vertical dot resolution, with a choice of 2 colors in each 8-dot by 8-dot section.

Bit map mode is selected (turned ON) by setting bit 5 of the VIC-II control register to a 1 at location 53265 ($DOll in HEX). The following

POKE will do this:

POKE 53265,PEEK(53265)OR 32

Bit map mode is turned OFF by setting bit 5 of the VIC-II control register to 0 at location 53265 ($D011), like this:

POKE 53265,PEEK(53265)AND 223

Before we get into the details of the bit map mode, there is one more issue to tackle, and that is where to locate the bit map area.

HOW IT WORKS

If you remember the

PROGRAMMABLE

CHARACTERS

recall that you were able to set the bit pattern of a character stored in

RAMto almost anything you wanted.

If at the same time you change the character that is displayed on the screen, you would be able to change a single dot, and watch it happen.

This is the basis of bit-mapping.

The

122 PROGRAMMING GRAPHICS

entire screen is filled with programmable characters, and you make your changes directly into the memory that the programmable characters get their patterns from.

Each of the locations in screen memory that were used to control what character was displayed, are now used for color information.

For example, instead of POKEing a 1 in location 1024 to make an "A" appear in the top left hand corner of the screen, location 1024 now controls the colors of the bits in that top left space.

Colors of squares in bit map mode do not come from color memory, as they do in the character modes.

Instead, colors are taken from screen memory. The upper 4 bits of screen memory become the color of any bit that is set to 1 in the 8 by 8 area controlled by that screen memory location. The lower 4 bits become the color of any bit that is set to a O.

EXAMPLE: Type the following:

5 BASE=2~4096:POKE53272,PEEK(53272)OR8:REM

MAP AT 8192

10 POKE53265,PEEK(53265)OR32:REM

PUT BIT

ENTER BIT MAP MODE

Now RUN the program.

Garbage appears on the screen, right? Just like the normal screen mode, you have to clear the HIGH-RESOLUTION(HI-RES) screen before you use it. Unfortunately, printing a CLRwon't work in this case. Instead you have to clear out the section of memory that you're using for your programmable characters.

Hit the .:UIlr~"IIIJ:1 .:I~"IIII:I:IIkeys, then add the following lines to your program to clear the HI-RES screen:

20 FORI=BASETOBASE+7999:POKEI,0:NEXT:REM

MAP

30 FORI=1024T02023:POKEI,3:NEXT:REM

C'T'At.~

Arm BLACK

CLEAR BIT

SET COLOR TO

Now RUN the program again.

You should see the screen clearing, then the greenish blue color, cyan, should cover the whole screen. What we want to do now is to turn the dots on and off on the HI-RES screen.

PROGRAMMING GRAPHICS

123

To SET a dot (turn a dot ON) or UNSETa dot (turn a dot OFF) you must know how to find the correct bit in the character memory that you have to set to a 1. In other words, you have to find the character you need to change, the row of the character, and which bit of the row that you have to change.

You need a formula to calculate this.

We will use X and Y to stand for the horizontal and vertical positions of a dot. The dot where x=o and y=o is at the upper-left of the display. Dots to the right have higher X values, and the dots toward the bottom have higher Y values.

The best way to use bit mapping is to arrange the bit map display something like this:

O__n___n_n_n___u_nn_n__nn___n_n_n__ X 000000_00__00_00_0000_0000_00_00_00_00___00 319 y

199 _nOnn_nnn___ __nn_n___nn_nn_n_nn___nn_n_n__nn nnn_nnnnnn_n___

Each dot will have an X and a Y coordinate.

With this format it is easy to control any dot on the screen.

124

PROGRAMMING GRAPHICS

Zo

=;3

!l.0

1--

°3

OCr!

u~ w

(/)

However, what you actually have is something like this:

BYTE 0

BYTE 1

BYTE 2.

BYTE 3

BYTE 4

BYTE 5_

BYTE 6

BYTE7

BYTE 8

BYTE 9

BYTE 10

BYTE 11

BYTE 12

BYTE 13

BYTE 14

BYTE 15

BYTE 16 BYTE 24

. . . . . . . . .

BYTE 312

BYTE313

BYTE314

BYTE315

BYTE316

BYTE317

BYTE318

BYTE319

BYTE 320 BYTE 328 BYTE 336- BYTE 344

BYTE 321 BYTE 329

BYTE 322 BYTE 330

BYTE 323 BYTE 331

BYTE 324 BYTE 332

BYTE 325 BYTE 333

BYTE 326 BYTE 334

BYTE 327 BYTE 335

. . . . . . .

BYTE 632

BYTE 633

BYTE 634

BYTE 635

BYTE 636

BYTE 637

BYTE 638

BYTE

639

The programmable characters which make up the bit map are arranged in 25 rows of 40 columns each.

While this is a good method of organization for text, it makes bit mapping somewhat difficult. (There is a good reason for this method, See the section on MIXED MODES.)

The following formula will make it easier to control a dot on the bit map screen:

The- start of the display memory area is known as the BASE. The row number (from 0 to 24) of your dot is:

ROW

INT(Y/8) (There are 320 bytes per line.)

The character position on that line (from 0 to 39) is:

CHAR

INT(x/8) (There are 8 bytes per character.)

The line of that character position (from 0 to 7) is:

LINE

Y AND 7

PROGRAMMING GRAPHICS 125

The bit of that byte is:

BIT

7-(X AND 7)

Now we put these formulas together.

The byte in which character memory dot (X,Y) is located is calculated by:

BYTE

BASE+ ROW320+ CHAR8+ LINE

To turn on any bit on the grid with coordinates (X,V), use this line:

POKE BYTE, P.EEK(BYTE) OR 2jBIT

Let's add these calculations to the program.

In the following example, the COMMODORE 64 will plot a sine curve:

5121 FOR:X:=0T0319STEP.

5: REr1 WAVE WILL FILL

60 Y=INTC9121+80:f.SINCX/1121»

7(1 CH= I tH C;";/8::-

8121 RO=INTC'T'/8::-

85 UI='r'AND7

90 B'T'=BASE +RO*32121+8*CH+L~1

11121 POKEB'r'" PEEK CB'r' ::0OR 0:2 t:E: I ::-

12121 t'IE:":n~

125 POKE1024..16

13121 GOT0130

THE SCREE~I

The calculation in line 60 will change the values for the sine function from a range of + 1 to -1 to a range of 10 to 170. Lines 70 to 100 calculate the character, row, byte, and bit being affected, using the formulae as shown above.

Line 125 signals the program is finished by changing the color of the top left corner of the screen.

Line 130 freezes the program by putting it into an infinite loop. When you have finished looking at the display, just hold down .:m/'~"tI'I:Iand hit .'1:1.'11I1'1:11.

126 PROGRAMMING GRAPHICS

As a further example, you can modify the sine curve program to displaya semicircle.

Here are the lines to type to make the changes:

50 FORX=0T0160:REM DO HALF THE SCREEN

'T'

1 iZII21+SC!F: ( 161?!,jo::x:-:;<::t.;:.::)

56 Y2=100-SQR(160:t.X-X*X)

60 FORY=Y1TOY2STEPY1-Y2

7121

CH= nn (:x:/:::)

80 RO=U-ITCT'/8)

U'I='T'AND7

BY=BASE+RO*320+S:t.CH+LN

10tC1 E:I=7-C<:At'1Dn

1 H3 POKEB'T'., PEEK (B'T') OR (2 'T'BI )

114 ~IEXT

This will create a semicircle in the HI-RES area of the screen.

WARNING: BASIC variables can overlay your high-resolutionscreen. If you need more memory space you must move the bottom of BASIC above the high-resolution screen area. Or, you must move your high-resolution will

NOT occur in machine language.

ItONLY happens when you're writing programs

BASIC.

MULTI-COLOR

BIT MAP MODE

Like multi-color mode characters, multi-color bit map mode allows you to display up to four different colors in each 8 by 8 section of bit map.

And as in multi-character mode, there is a sacrifice of horizontal resolution (from 320 dots to 160 dots).

Multi-color bit map mode uses an 8K section of memory for the bit map.

You select your colors for multi-color bit map mode from (1) the background color register 0, (the screen background color), (2) the video matrix (the upper 4 bits give one possible color, the lower 4 bits another), and (3) color memory.

Multi-color bit mapped mode is turned ON by setting bit 5 of 53265

($D011) and bit 4 at location 53270 ($D016) to a 1. The following POKE does this:

POKE 53265,PEEK(53625)OR 32: POKE 53270,PEEK(53270)OR 16

PROGRAMMING GRAPHICS 127

Multi-color bit mapped mode is turned OFF by setting bit 5 of 53265

($0011) and bit 4 at location 53270 ($0016) to a O. The following POKE does this:

POKE 53265,PEEK(53265)AND 223: POKE 53270,PEEK(53270)AND 239

As in standard (HI-RES) bit mapped mode, there is a one to one correspondence between the 8K section of memory being used for the display, and what is shown on the screen. However, the horizontal dots are two bits wide. Each 2 bits in the display memory area form a dot, which can have one of 4 colors.

BITS

COLOR

INFORMATION COMES FROM

Background color #0 (screen color)

Upper 4 bits of screen memory lower 4 bits of screen memory

Color nybble (nybble

1/2 byte

4 bits)

SMOOTH SCROLLING

The VIC-II

chip supports smooth scrolling in both the horizontal and

vertical directions.

Smooth scrolling is a one pixel movement of the entire screen in one direction. It can move either up, or down, or left, or right. It is used to move new information smoothly onto the screen, while smoothly removirlg characters from the other side.

While the VIC-II chip does much of the task for you, the actual scrolling must be done by a machine language program.

The VIC-II chip features the ability to place the video screen in any of 8 horizontal positions, and 8 vertical positions.

Positioning is controlled by the VIC-II scrolling registers. The VIC-II chip also has a 38 column mode, and a 24 row mode. the smaller screen sizes are used to give you a place for your new data to scroll on from.

The following are the steps for SMOOTH SCROLLING:

128

1) Shrink the screen (the border will expand).

2) Set the scrolling register to maximum (or minimum value depending upon the direction of your scroll).

3) Place the new data on the proper (covered) portion of the screen.

4) Increment (or decrement) the scrolling register until it reaches the maximum (or minimum) value.

5) At this point, use your machine language routine to shift the entire screen one entire character in the direction of the scroll.

6) Go back to step 2.

To go into 38 column mode, bit 3 of location 53270 ($D016) must be set to a O. The following POKE does this:

POKE 53270,PEEK(53270)AND 247

To return to 40 column mode, set bit 3 of location 53270 ($D016) to a

1. The following POKE does this:

POKE 53270,PEEK(53270)OR 8

To go into 24 row mode, bit 3 of location 53265 ($D011) must be set to a O. The following POKE will do this:

POKE 53265,PEEK(53265)AND 247

To return to 25 row mode, set bit 3 of location 53265 ($DOll) to a 1.

The following POKE does this:

POKE 53265,PEEK(53265)OR 8

Whe, scrolling in the X direction, it is necessary to place "the VIC-II chip into 38 column mode. This gives new data a place to scroll from.

When scrolling LEFT,the new data should be placed on the right. When scrolling RIGHT the new data should be placed on the left. Please note that there are still 40 columns to screen memory, but only 38 are visible.

When scrolling in the Ydirection, it is necessary to place the VIC-II chip into 24 row mode. When scrolling UP, place the new data in the LAST row. When scrolling DOWN, place the new data on the FIRST row. Unlike X scrolling, where there are covered areas on each side of the screen, there is only one covered area in Y scrolling. When the Y scroll-

PROGRAMMING 129

ing register is set to 0, the first line is covered, ready for new data.

When the Y scrolling register is set to 7 the last row is covered.

For scrolling in the X direction, the scroll register is located in bits 2 to o of the VIC-II control register at location 53270 ($DOI6 in HEX). As always, it is important to affect only those bits. The following POKE does this:

POKE 53270, (PEEK(53270)AND 248)+X where X is the X position of the screen from 0 to 7.

For scrolling in the Y direction, the scroll register is located in bits 2 to o of the VIC-II control register at location 53265 ($DOII in HEX). As always, it is important to affect only those bits. The following POKE does this:

POKE 53265, (PEEK(53265)AND 248)+Y where Y is the Y position of the screen from 0 to 7.

To scroll text onto the screen from the bottom, you would step the low-order 3 bits of location 53265 from 0-7, put more data on the covered line at the bottom of the screen, and then repeat the process.

To scroll characters onto the screen from left to right, you would step the low-order 3 bits of location 53270 from 0 to 7, print or POKE another column of new data into column 0 of the screen, then repeat the process.

If you step the scroll bits by -I, your text will move in the opposite direction.

EXAMPLE:Text scrolling onto the bottom of the screen:

10 POKE53265,PEEK(53265)AND247

INTO 24 ROW MODE

2121PRINTCHR$(147)

CLEAR THE SCREEN

30 FORX=lT024:PRINTCHR$(17); :NEXT

THE CURSOR TO THE BOTTOM

40 POKE53265,(PEEK(53265)AND248)+7:PRINT

POSITION FOR 1ST SCROLL

5121

PRItH

HELLO

;

6121FORP=6T00STEP-1

70 POKE53265,(PEEK(53265>AND24S)+P

:REM GO

:REM

:REM MOVE

:REr1

:REM

DELAo,.' LOOP

910 t~E:>o:T:

130 PROGRAMMING GRAPHICS

SPRITES

A SPRITE is a special type of user definable character which can be displayed anywhere on the screen.

Sprites are maintained directly by the VIC-II chip. And all you have to do is tell a sprite "what to look like,"

"what color to be," and "where to appear." The V/C-II chip will do the rest! Sprites can be any of the 16 colors available.

Sprites can be used with ANY of the other graphics modes, bit

":lapped, character, multi-color, etc., and they'll keep their shape in all of them. The sprite carries its own color definition, its own mode (HI-RES or multi-colored), and its own shape.

Up to 8 sprites at a time can be maintained by the VIC-II chip automatically.

More sprites can be displayed using RASTER INTERRUPT techniques.

The features of SPRITES include:

1) 24 horizontal dot by 21 vertical dot size.

2) Individual color control for each sprite.

3) Sprite multi-color mode.

4) Magnification (2X) in horizontal, vertical, or both directions.

5) Selectable sprite to background priority.

6) Fixed sprite to sprite priorities.

7) Sprite to sprite collision detection.

8) Sprite to background collision detection.

These special sprite abilities make it simple to program many arcade style games.

Because the sprites are maintained by hardware, it is even possible to write a good quality game in BASIC!

Th( r.3 are 8 sprites supported directly by the VIC-II chip. They are numbered from 0 to 7. Each of the sprites has it own definition location, position registers and color register, and has its own bits for enable and collision detection.

DEFINING A SPRITE

Sprites are defined like programmable characters are defined.

However, since the size of the sprite is larger, more bytes are needed.

A sprite is 24 by 21 dots, or 504 dots. This works out to 63 bytes (504/8

PROGRAMMING

131

Co)

COLUMN

NUMBER

..,

BIT

BIT DATA

VALUES

(ON .dxVAL)

ROW0

"'II

10.

iiJ

..,

J: n .

Co) to.)

ROW1

ROW2

ROW3

ROW4

...

:;:

:!)

:;: ir

D:J

ROW5

ROW6

ROW7

ROW8

ROW9

ROW10

ROW11

ROW12

ROW13

ROW14

ROW15

ROW16

ROW17

ROW18

ROW19

ROW20

01 02 03 04 05

08 09

7 6 5 4

128 64

32 16

10 11 12

15 16 17 18

21 22

5 4

128 64

32 16

6 5 4

128 64 32

bits) needed to define a sprite. The 63 bytes are arranged in 21 rows of

3 bytes each.

A sprite definition looks like this:

BYTE0

BYTE3

BYTE6

BYTE 1

BYTE4

BYTE7

BYTE2

BYTE5

BYTE8

BYTE 60 BYTE 61

BYTE 62

Another way to view how a sprite is created is to take a look at the sprite definition block on the bit level. It would look something like Figure

3-2.

In a standard (HI~RES)sprite, each bit set to 1 is displayed in that sprite's foreground color. Each bit set to 0 is transparent and will display whatever data is behind it. This is similar to a standard character.

Multi-color sprites are similar to multi-color characters.

Horizontal resolution is traded for extra color resolution. The resolution of the sprite becomes 12 horizontal dots by 21 vertical dots. Each dot in the sprite becomes twice as wide, but the number of colors displayable in the sprite is increased to 4.

SPRITE

POINTERS

Even though each sprite takes only 63 bytes to define, one more byte is needed as a place holder at the end of each sprite. Each sprite, then, takes up 64 bytes. This makes it easy to calculate where in memory your sprite definition is, since 64 bytes is an even number and in binary it's an even power.

EC'ch of the 8 sprites has a byte associated with it called the SPRITE

POINTER.The sprite pointers control where each sprite definition is located in memory. These 8 bytes are always located as the last 8 bytes of the 1K chunk of screen memory.

Normally, on the Commodore 64, this means they begin at location 2040 ($07F8 in HEX). However, if you move the screen, the location of your sprite pointers will also move.

Each sprite pointer can hold a number from 0 to 255. This number points to the definition for that sprite. Since each sprite definition takes

64 bytes, that means that the pointer can "see" anywhere in the 16K block of memory that the VIC-II chip can access (since 256*64= 16K).

PROGRAMMING GRAPHICS 133

If sprite pointer #0, at location 2040, contains the number 14, for example, this means that sprite 0 will be displayed using the 64 bytes beginning at location 14*64

896 which is in the cassette buffer. The following formula makes this clear:

LOCATION

(BANK * 16384) + (SPRITE POINTER VALUE* 64)

Where BANK is the 16K segment of memory that the VIC-II chip is looking at and is fr~m 0 to 3.

The above formula gives the start of the 64 bytes of the sprite definition block.

When the VIC-II chip is looking at BANK 0 or BANK 2, there is a ROM

IMAGE of the character set present in certain locations, as mentioned before.

Sprite definitions can NOT be placed there.

If for some reason you need more than 128 different sprite definitions, you should use one of the banks without the ROM IMAGE, 1 or 3.

TURNING SPRITES ON

The VIC-II control register at location 53269 ($D015 in HEX) is known as the

SPRITE ENABLE

Each of the sprites has a bit in this register which controls whether that sprite is ON or OFF. The register looks like this:

$D015 7 6 5 4 3 2 1 0

To turn on sprite 1, for example, it is necessary to turn that bit to a I.

The following POKE does this:

POKE 53269,PEEK(53269)OR 2

A more general statement would be the following:

POKE 53269,PEEK(53269}OR (2tSN) where SN is the sprite number, from 0 to 7.

NOTE: A sprite must be turned ON before it con be seen.

134 'PROGRAMMING GRAPHICS

TURNING SPRITES OFF

A sprite is turned off by setting its bit in the VIC-lIcontrol register at

53269 ($0015 in HEX) to a O. The following POKE will do this:

POKE 53269, PEEK(53269)AND (255-2jSN) where SN is the sprite number from 0 to 7.

COLORS

A sprite can be any of the 16 colors generated by the VIC-II chip.

Each of the sprites has its own sprite color register. These are the memory locations of the color registers:

ADDRESS

DESCRIPTION

53287

53288

53289

53290

53291

53292

53293

53294

($0027)

($0028)

($0029)

($002A)

($0026)

($002C)

($0020)

($002E)

SPRITE 0 COLOR REGISTER

SPRITE 1 COLOR REGISTER

SPRITE 2 COLOR REGISTER

SPRITE 3 COLOR REGISTER

SPRITE 4 COLOR REGISTER

SPRITE 5 COLOR REGISTER

SPRITE 6 COLOR REGISTER

SPRITE 7 COLOR REGISTER

All dots in the sprite will be displayed in the color contained in the sprite color register.

The rest of the sprite will be transparent, and will show whatever is behind the sprite.

MULTI-COLOR MODE

Multi-color mode allows you to have up to 4 different colors in each sprite. However, just like other multi-color modes, horizontal resolution is cut in half. In other words, when you're working with sprite multi-color mode (like in multi-color character mode), instead of 24 dots across the sprite, there are 12 pairs of dots. Each pair of dots is called a BIT PAIR.

Think of each bit pair (pair of dots) as a single dot in your overall sprite when it comes to choosing colors for the dots in your sprites. The table

PROGRAMMING

GRAPHICS 135

below gives you the bit pair values needed to turn ON each of the four colors you've chosen for your sprite:

BIT PAIR DESCRIPTION

TRANSPARENT,SCREEN COLOR

SPRITE MULTI-COLORREGISTER#0 (53285) ($D025)

SPRITE COLOR REGISTER

SPRITEMULTI-COLORREGISTER#1 (53286) ($D026)

NOTE: The sprite foreground color is a 10. The character foreground is a 11.

SEnlNG

A

SPRITE TO MULTI-COLORMODE

To switch a sprite into multi-color mode you must turn ON the VIC-II control register at location 53276 ($D01 C). The following POKE does this:

POKE 53276,PEEK(53276) OR (2tSN) where SN is the sprite number (O to 7).

To switch a sprite out of multi-color mode you must turn OFF the VIC-II control register at location 53276 ($D01C). The following POKE

does this:

POKE 53276,PEEK(53276) AND (255-2tSN) where SN is the sprite number (O to 7).

EXPANDED

SPRITES

The VIC-II chip has the ability to expand a sprite in the vertical direction, the horizontal direction, or both at once. When expanded, each dot in the sprite is twice as wide or twice as tall. Resolution doesn't actually increase.

. . the sprite just gets bigger.

To expand a sprite in the horizontal direction, the corresponding bit in

the VIC-II control register at location

53277 ($D01

D in HEX)must be turned

(set to a 1). The following

POKE

expands a sprite in the X

direction:

POKE 53277,PEEK(53277)OR (2tSN) where SN is the sprite number from 0 to 7.

136 PROGRAMMING GRAPHICS

To unexpand a sprite in the horizontal direction, the corresponding bit in the VIC-II control register at location 53277 ($DOID in HEX) must be turned OFF (set to a 0). The following POKE "unexpands" a sprite in the

X direction:

POKE 53277,PEEK(53277)AND (255-2tSN) where SN is the sprite number from 0 to 7.

To expand a sprite in the vertical direction, the corresponding bit in the VIC-II control register at location 53271 ($DOI7 in HEX) must be turned ON (set to a 1). The following POKE expands a sprite in the Y direction:

POKE 53271, PEEK{53271)OR (2tSN) where SN is the sprite number from 0 to 7.

To unexpand a sprite in the vertical direction, the corresponding bit in the VIC-II control register at location 53271 ($DOI7 in HEX) must be turned OFF (set to a 0). The following POKE "unexpands" a sprite in the

Y direction:

POKE 53271,PEEK(53271)AND (255-2tSN) where SN is the sprite number from 0 to 7.

SPRITE

POSITIONING

Once you've made a sprite you want to be able to move it around the screen. To do this, your Commodore 64 uses three positioning registers:

1) SPRITE X POSITION REGISTER

2) SPRITE Y POSITION REGISTER

3) MOST SIGNIFICANT BIT X POSITION REGISTER

Each sprite has an X position register, a Y position register, and a bit in the X most significant bit register.

This lets you position your sprites very accurately.

You can place your sprite in 512 possible X positions and 256 possible Y positions.

The X and Y position registers work together, in pairs, as a team. The locatkms of the X and Y registers appear in the memory map as follows:

First is the X register for sprite 0, then the Y register for sprite O. Next

PROGRAMMING 137

comes the X register for sprite 1, the Y register for sprite 1, and so on.

After all 16 X and Y registers comes the most significant bit in the X position (X MSB) located in its own register.

The chart below lists the locations of each sprite position register.

You use the locations at their appropriate time through

POKE

statements:

LOCATION

DECIMAL

HEX

53248

53249

53250

53251

53252

53253

53254

53255

53256

53257

53258

53259

53260

53261

53262

53263

53264

($DOOO)

($DOOI )

($D002)

($D003)

($D004)

($D005)

($ D006)

($D007)

($D008)

($D009)

($ DOOA)

($DOOB)

($ DOOC)

($DOOD)

($DOOE)

($DOOF)

($D010)

DESCRIPTION

SPRITE 0 X POSITION REGISTER

SPRITE 0 Y POSITION REGISTER

SPRITE 1 X POSITION REGISTER

SPRITE 1 Y POSITION REGISTER

SPRITE 2 X POSITION REGISTER

SPRITE 2 Y POSITION REGISTER

SPRITE 3 X POSITION REGISTER

SPRITE 3 Y POSITION REGISTER

SPRITE 4 X POSITION REGISTER

SPRITE 4 Y POSITION REGISTER

SPRITE 5 X POSITION REGISTER

SPRITE 5 Y POSITION REGISTER

SPRITE 6 X POSITION REGISTER

SPRITE 6 Y POSITION REGISTER

SPRITE 7 X POSITION REGISTER

SPRITE 7 Y POSITION REGISTER

SPRITE X MSB REGISTER

The position of a sprite is calculated from the TOP LEFTcorner of the

24 dot by 21 dot area that your sprite can be designed in. It does NOT matter how many or how few dots you use to make up a sprite.

Even if only one dot is used as a sprite, and you happen to want it in the middle of the screen, you must still calculate the exact positioning by starting at the top left corner location.

VERTICAL POSITIONING

Setting up positions in the horizontal direction is a little more difficult than vertical positioning, so we'll discuss vertical (Y) positioning first.

There are 200 different dot positions that can be individually programmed onto your TV screen in the Y direction.

The sprite Y position registers can handle numbers up to 255. This means that you have more

138

than enough register locations to handle moving a sprite up and down.

You also want to be able to smoothly move a sprite on and off the screen.

More than 200 values are needed for this.

The first on-screen value from the top of the screen, and in the Y direction for an unexpanded sprite is 30. For a sprite expanded in the Y direction it would be 9. (Since each dot is twice as tall, this makes a certain amount of sense, as the initial position is STILLcalculated from the top left corner of the sprite.)

The first Y value in which a sprite (expanded or not) is fully on the screen (all 21 possible lines displayed) is 50.

The last Y value in which an unexpanded sprite is fully on the screen is

229. The last Y value in which an expanded sprite is fully on the screen is 208.

The first Y value in which a sprite is fully off the screen is 250.

EXAMPLE:

---mD~

1121 -

20 POKE2040

, 13

DATA FROM BLOCK 13

30 FORI=OT062:POKE832+I,129'NEXT:REM

DATA INTO BLOCK 13 (13*64=832)

40 V=53248

OF VIDEO CHIP

5121POKEV+21" 1

60 pm~E""'+:39., 1

COLOR

71<:1POKE '+ 1 " 11210

'T' POSITIO~I

80 POKEV+16,0:POKEV,100

>': POSITION

: REt'1 CLEAF.: SCF.:EEt,1

:REM GET SPRITE 0

POKE SPRITE

:REM

SET

BEGINNING

: F.'Et1 EI"IABLE ~;PRITE

:REM SET SPRITE (1

:REM SET SPRITE 0

:REM SET SPRITE 121

HORIZONTAL POSITIONING

Positioning in the horizontal direction is more complicated because there are more than 256 positions. This means that an extra bit, or 9th bit is used to control the X position. By adding the extra bit when necessary a sprite now has 512 possible positions in the left/right, X, direction. This makes more possible combinations than can be seen on the visible part of the screen. Each sprite can have a position from 0 to 511.

However, only those values between 24 and 343 are visible on the screen.

If the X position of a sprite is greater than 255 (on the right side of the screen), the bit in the X MOST SIGNIFICANTBIT POSITION register must be set to a 1 (turned ON). If the X position of a sprite is less than

PROGRAMMING

139

...

o

~

Z

...

:r n

C/I

29 (S1D) o (SOO) 24 (S18)

I I

-- -

50 (S32)

___I

VISIBLE VIEWING AREA

296 (S128)

344 ($158)

1 8 ($08)

50 ($32)

'ft cO.

;

Co)

Co) en

...

:;:

NTSC'

40 COLUMNS

25 ROWS

208 ($DO)-

250 (SFA)-I

488 (S1E8)

24 (S18)

.North American televisiontransmissionstandards for your home TV.

-- -

250 ($FA)

320 (S140)

I

344 (S158)

229 ($E5)

G')

~ n

"'" o

G')

co

:sa

::I-

II>

:;:

~ cr

!II

33 ($211

7 ($07) 31 ($1F)

I

I I

I 1

I I

I 1

__ - _1__1

54 ($36) I

287 ($11FI

335 ($14FI

, 1- _ _ _ _ _ _ 12 ($OC)

- - 54 ($36)

VISIBLE VIEWING AREA

NTSC.

38 COLUMNS

24 ROWS

246 ($F6)- -,

480 ($1EO)

31 ($1F)

.North

American television transmission standards for your home TV.

- ---225 ($E1)

- - - -246 I$F6)

311 ($137)

335 ($14FI

256 (on the left side of the screen), then the X MSB of that sprite must be 0 (turned OFF). Bits 0 to 7 of the X MSB register correspond to sprites o to 7, respectively.

The following program moves a sprite across the screen:

EXAMPLE:

--IDIIiI"

10 PF.:It-IT"::T'-

20 F'OKE2040.13

30 FORI=0T062:POKE832+I.129:NEXT

..,.=5:324:3

50 POKE'.'!+21,. 1

6121POKE"'!+3S<..1

70 POKEV+ 1 " 1121(1

8121FOF(J=!3TOcH7

90 HX=INTeJ/256)'LX=J-256*HX

100 POKEV.LX:POKEV+16.HX:NE~T

When moving expanded sprites onto the left side of the screen in the

X direction, you have to start the sprite

OFF SCREEN

on the

RIGHTSIDE.

This

is because an expanded sprite is larger than the amount of space available on the left side of the screen.

EXAMPLE:

,ABI"

1121pF.:nn":J"

2(1 F'OKE2!~140.

FORI=0T062:POKE832+I.129:NEXT

4121 \.':=::5::':248

50 POKE','!+21"

60 POKEV+39.1:POKEV+23.1:POKEV+29.1

70 POKE'.,!+1 . 10(~

:3121J~48:::

90 HX=INTeJ/256):LX=J-256*HX

100 POKEV,LX:POKEV+16.HX

110 J=J+l:IFJ)511THENJ=0

120 IFJ)4880RJ<348GOT090

The charts in Figure 3-3 explain sprite positioning.

By using these values, you can position each sprite anywhere.

By moving the sprite a single dot position at a time, very smooth movement is easy to achieve.

142 PROGRAMMING GRAPHICS

SPRITE POSITIONING SUMMARY

Unexpanded sprites are at least partially visible in the 40 column, by

25 row mode within the following parameters:

1 <

X

343

= y

< =

249

In the 38 column mode, the X parameters change to the following:

8 <

< = 334

In the 24 row mode, the Y parameters change to the following:

34 <

< =

245

Expanded sprites are at least partially visible in the 40 column, by 25 row mode within the following parameters:

489 >

343

> =

< =

249

In the 38 column mode, the X parameters change to the following:

1496>

< =

334

In the 24 row mode, the Y parameters change to the following:

13 <

Y <

245

PROGRAMMING GRAPHICS 143

SPRITE DISPLAY PRIORITIES

Sprites have-the ability to cross each other's paths, as well as cross in front of, or behind other objects on the screen. This can give you a truly three dimensional effect for games.

Sprite to sprite priority is fixed. That means that sprite 0 has the highest priority, sprite 1 has the next priority, and so on, until we get to sprite 7, which has the lowest priority. In other words, if sprite 1 and sprite 6 are positioned so that they cross each other, sprite 1 will be in front of sprite 6.

So when you're planning which sprites will appear to be in the foreground of the picture, they must be assigned lower sprite numbers than those sprites you want to put towards the back of the scene.

Those sprites will be given higher sprite numbers.

NOTE: A "window" effect is possible.

If a sprite with higher priority has "holes" in it

(areas where the dots are not set to 1 and thus turned ON), the sprite- with the lower priority will show through.

This also happens with sprite and background data.

Sprite to background priority is controllable by the SPRITE-BACK-

GROUND priority register located at 53275 ($DOIB). Each sprite has a bit in this register.

If that bit is 0, that sprite has a higher priority than the background on the screen.

In other words, the sprite appears in front of background data.

If that bit is aI, that sprite has a lower priority than the background.

Then the sprite appears behind the background data.

COLLISION DETECTS

One of the more interesting aspects of the VIC-II chip is its collision detection abilities.

Collisions can be detected between sprites, or between sprites and background data.

A collision occurs when a non-zero part of a sprite overlaps a non-zero portion of another sprite or characters on the screen.

144

SPRITE TO SPRITE COLLISIONS

Sprite to sprite collisions are recognized by the computer, or flagged, in the spite to sprite collision register at location 53278 ($DOl E in HEX) in the VIC-II chip control register.

Each sprite has a bit in this register.

If that bit is a 1, then that sprite is involved in a collision. The bits in this register will remain set until read (PEEKed). Once read, the register is automatically cleared, so it is a good idea to save the value in a variable until you are finished with it.

NOTE: Collisions can take place even when the sprites are off screen.

SPRITE TO DATA COLLISIONS

Sprite to data collisions are detected in the sprite to data collision register at location 53279 ($DOl F in HEX)of the VIC-II chip control register.

Each sprite has a bit in this register.

If that bit is a 1, then that sprite is involved in a collision. The bits in this register remain set until read

(PEEKed). Once read, the register is automatically cleared, so it is a good idea to save the value in a variable until you are finished with it.

NOTE: MULTI-COLORdata 01 is considered transparent for collisions, even though it shows up on the screen.

When setting up a background screen, it is a good idea to make everything that should not cause a collision 01 in multi-color mode.

PROGRAMMING GRAPHICS 145

10 REM SPRITE EXAMPLE 1...

20 REM THE HOT AIR BALLOON

30 VIC=13~4096:REM THIS IS WHERE THE VIC REGISTERS

BEGIN

35 POKEVIC+21,1:REM ENABLE SPRITE

36 POKEVIC+33, 14:REM SET BACKGROUND COLOR TO LIGHT

BLUE

37 POKEVIC+23,1:REM EXPAND SPRITE 0 IN Y

38 POKEVIC+29,1:REM EXPAND SPRITE 0 IN X

40 POKE2040 ,192:REM SET SPRITE 0~S POINTER

180 POKEVIC+0,100:REM SET SPRITE 0~S X POSITION

190 POKEVIC+l, 100:REM SET SPRITE 0~S Y POSITION

220

POKEVIC+39,1:REM SET SPRITE 0~S COLOR

250 FORY=0T063:REM BYTE COUNTER WITH SPRITE LOOP

300 READA:REM READ IN A BYTE

310 POKE192*64+Y,A:REM

AREA

320

I~EXT'T': CLOSE LOOP

STORE THE DATA IN SPRITE

330 DX=l:DY=l

340 X=PEEK(VIC):REM LOOK AT SPRITE 0~S X POSITION

350

360

Y=PEEK(VIC+l):REM LOOK AT SPRITE 0~S Y POSITION

IFY=500RY=208THENDY=-DY:REM IF Y IS ON THE

EDGE OF THE....

370 REt1 SCREEN, THEt~ REVERSE DELTA Y

380 IFX=24AND(PEEK(VIC+16)AND1)=0THENDX=-DX:REM

SPRITE IS....

390 REM TOUCHIt~GTHE LEFT EDGE (>::=24 At~DTHE MSB

FOR SPRITE 0 IS 0), REVERSE IT

400 IFX=40AND(PEEK(VIC+16)AND1)=lTHENDX=-DX:REM IF

SPRITE IS....

410 REI1 TOUCHI.NG

THE

RIGHT EDGE (X=40 AND THE t1SB

FOR SPRITE 0 IS 1), REVERSE IT

420IFX=255ANDDX=lTHENX=-1:SIDE=1

430 REM SWITCH TO OTHER SIDE OF THE SCREEN

440 IFX=0ANDDX=-lTHENX=256:SIDE=0

450 REM SWITCH TO OTHER SIDE OF THE SCREEN

460 X=X+DX:REM ADD DELTA X TO X

470 X=XAND255:REM MAKE SURE X IS IN ALLOWED RANOE

480 Y=Y+DY:REM

ADD DELTA Y TO Y

485 POKEVIC+16,SIDE

490 POKEVIC,X:REM PUT NEW X VALUE INTO SPRITE 0~S

X POSITION

510 POKEVIC+1,Y:REM PUT NEW Y VALUE INTO SPRITE

0~S 'i POSITION

530 OOT0340

600 REM *****

SPRITE DATA

*****

610 DATA0,127,0,1,255,192,3,255,224,3,231,224

620 DATA7,217,240,7,223,240,7,217,240,3,231,224

630 DATA3,255,224,3,255,224,2,255,160, 1,127,64

640 DATAl,62,64,0,156,128,e,156,128,0,73,a,a,73,a

650 DATA0,62,0,0,62,0,0,62,0,0,28,a,0

146 PROGRAMMING GRAPHICS

10 REt'l SPRITE

E:":AMPLE 2...

20 REM THE HOT AIR BALLOON AGAIN

30 VIC=13*4096:REM

BEGIN

THIS IS WHERE THE VIC REGISTERS

35 POKEVIC+21,63:REM ENABLE SPRITES 0 THRU 5

POKE"I

IC+33., 14 :REM SET BACKGROUt.jD

COLOR TO LIGHT

:BLUE

POKE"lIC+23.,:3:

REf'l

E:";PAND SPRITES 0 AND 1 IN 'T'

38 POKEY I C+29.,

3 : REt1 E>::PAt~D SPR

IrES 0 AND 1 HI X

40 POKE2040, 192:REM SET SPRITE 0~S POINTER

50 POKE2041 , 193:REM SET SPRITE l~S POINTER

60 POKE2042, 192:REM SET SPRITE 2~S POINTER

70 POKE2043, 193:REM SET SPRITE 3~S POINTER

80 POKE2044..

192:REM SET

SPRITE 4~S POINTER

90 POKE2045, 193:REM SET SPRITE 5~S POINTER

100 POKEVIC+4,30:REM SET SPRITE 2~S X POSITION

110 POKEY I C+5, 58 :REM

120 POKEVIC+6,65:REM

SET SPR ITE 2 ~ S ',JPOS I TI ON

SET SPRITE 3~S X POSITION

130 POKEVIC+7,58:REM SET SPRITE 3'S Y POSITION

140 POKEVIC+8, 100:REM SET SPRITE 4~S X POSITION

150 POKEVIC+9,58:REM SET SPRITE 4~S Y POSITION

160 POKEVIC+10, 100:REM SET SPRITE 5'S X POSITION

17(1 POKE..,.I C+ 11 , 58 :REM SET SPR IrE 5' S Y POS IT IO~!

J81J

175 PRINT" i:(']"TAB( IS TWO HIRES SPRITES".;

'mil"

176 PR HITTAB (55) "Ot.!

TOP OF EACH OTHER"

180 POKEVIC+0, 100:REM

SET SPRITE 0~S X POSITION

190 POKEVIC+1, 100:REM SET SPRITE 0'S Y POSITION

200 POKEVIC+2, 100:REM SET SPRITE l'S X POSITION

210 POKEVIC+3, 100:REM SET SPRITE l~S Y POSITION

220 POKEVIC+39,1:REM

230 POKEVIC+41,1:REM

240 POKEVIC+43,1:REM

SET

SPRITE

0'S

2~S

4'S

COLOR

.250

POKEV I C+40., 6 :REt1 SET

260 POKEVIC+42,6:REM SET

SPFU TE l' S COLOF.:

SPRITE 3'S COLOR

270 POKEVIC+44,6:REM

SET SPRITE

5'S COLOR

280 FORX=192T0193:REM THE START OF THE LOOP THAT

DEFINES THE SPRITES

290 FORY=0T063:REM BYTE COUNTER WITH SPRITE LOOP

300 READA:REMREAD

IN A BYTE

:310 POKE~<::+:64+Y, STORE THE DATA It-!

SPR ITE AREFI

320 NEXTY,X:REM CLOSE LOOPS

330 D>::= 1 :DY= 1

340 X=PEEK(VIC):REM LOOK AT SPRITE 0~S X POSITION

350 Y=PEEK(VIC+l):REM LOOK AT SPRITE 0'S Y POSITION

360 IF'T'=500RY=208THEND'r'=-DY: REt1 IF 'T' IS ON THE

EDGE OF THE...

370 REM SCREEN, THEN REVERSE DELTA Y

SPRITE

IS...

390 REM TOUCHING THE LEFT EDGE, THEN REVERSE IT

PROGRAMMING GRAPHICS

147

400 I FK=40FH.m

0::PEEK 0::I.,.'I C+ 16) At.m 1)

SPRITE IS...

1THE~m>,;=- Dr.:: REt1 IF

410 REM TOUCHING THE RIGHT

EDGE,

THEN REVERSE IT

420 IFX=255ANDDX=1THENX=-1:SIDE=3

43(1 REt1 SJ..JITCH

TO OTHER S I DE OF THE SCREEN

440 IF:.:=0At.mm':=-1 THEN:X:=256: SIDE=0

450 REM SWITCH TO OTHER SIDE OF THE SCREEN

460 :.:=:.:+m,:: REt1 ADD DELTA ::-::TO :.:

470 X=XAND255:REM MAKE SURE X IS IN ALLOWED RANGE

480 Y=Y+DY:REM ADD DELTA Y TO Y

485 POKEVIC+16,SIDE

490 POKEVIC,X:REM PUT NEW X VALUE INTO SPRITE O'S

?~ POSITIm~

500 POKEVIC+2, >:::REt1 PUT ~~EW:x: I'..'ALUE uno SPRITE

1 ':3 :.: POS IT ION

510 POKEVIC+l.Y:REM PUT NEW Y VALUE INTO SPRITE

O'S Y POSITIO~~

520 POKEV!C+3,Y:REM

1'S 'r POSITIO~~

PUT NEW Y VALUE INTO

530 GOT0340

600 REM ***** SPRITE DATA *****

SPRITE

610

DATA0,255,0,3,153,192,7,24,224,7,56,224,14,

112,14,126,112,14,126,112

620 DATA6, 126,96,7,56,224,7,56,224,i,56,128,O,153,

0,0,90, (I, 0, 56.. °

6313 DATAO,56,0,0,0,O,O,O,O,O,12G,e,e,42,e,0,84,e,o,

413..0,0

640 DATAo,e,O,0,102,0,0,231,0,0,195,0,i,129,128,1,

129,128,1,129,128

650 DATA1,12~,128,0,195,O,0,195,0,4,195,32,2,102,

64,2,36,64,1,0,128

660 DATA1,0,128,0,153,O,O,153,O,O,0,O,0,84,0,O,42,

O,O,20,O,O

126,

10 REt1 SPR ITE EXAMPLE

3...

213 REM THE HOT AIR GORF

30 VIC=53248:REM THIS IS WHERE THE VIC REGISTERS

BEGIN

35 POKEVIC+21,1: REME~IABLESPRITE 0

148

PROGRAMMING GRAPHICS

36 POKEVIC+33, 14:REM SET BACKGROUND COLOR TO LIGHT

B..LUE

37 POKEVIC+23,1:REM

38 POKE~IC+29,1:REM

EXPAND SPRITE 121IN ~

EXPAND SPRITE 121IN X

40 POKE2€140, 192: REM SET SPRITE 0'8 PO HnEI':

5121

F'OKEVIC+28, 1 :REt1 TURN O~j MUL TICOLOR

60 POKEVIC+37,7:REM

7121POKEVIC+38,4:REM

SET MULTICOLOR

121

180 POKEVIC+I2I, 1121121: SET SPRITE

19121POKEVIC+1., 112110: SET SPRITE

22121

F'OKEVIC+39.. 2: REt1 SET SPRITE e's X POSITION et'S 'T'POSITION

I2I'S COLOR

2910

3121121

FORY=etT063:REM BYTE COUNTER WITH SPRITE LOOP

READA:REM READ IN A BYTE

31121 POKE12288+Y,A:REM STORE THE DATA IN SPRITE AREA

32121

NEXT Y:REM CLOSE LOOP

33121 D;:<:=

1 :DY= 1

34121

35121Y=PEEK(VIC+1):REM LOOK AT SPRITE IZI'S~ POSITION

36121IFY=500RY=21Z18THENDY=-DY:REM IF Y IS ON THE

EDGE OF THE...

87121REM SCREEN, THEN REVERSE DELTA Y

38121

IF X=24AND(PEEK(,.lIC+16)At~D1 )=0THEI.m:x;=-D:x:: REt"1

IF SPRITE IS...

39121REM TOUCHING THE LEFT EDGE, THEN REVERSE IT

SPRITE IS...

41121REM TOUCHING THE RIGHT EDGE, THEN REVERSE IT

42€1

F;:':=255A~mDX=

1 THE~jX=-1 :S I DE= 1

43121REM SWITCH TO OTHER SIDE OF THE SCREEN

44121 IFX=I2IANDDX=-1THENX=256:SIDE=1ZI

45121

REM SWITCH TO OTHER SIDE OF THE SCREEN

46121

X=X+DX:REM ADD DELTA X TO X

47121 >::=;x:At.JD255: REt1 MAKE SURE :";IS IH ALLm~ED

RAt.JGE

48121

Y=~+D~:REM ADD DELTA Y TO Y

485 POKEVIC+16,SIDE

49121 POKEVIC,X:REM

:>0:POS IT I OI.j

PUT HEW X VALUE IHTO SPRITE I2I'S

51121

POKEVIC+1.~:REM PUT HEW Y VALUE IHTO SPRITE

12I"S 'T'

POSITImJ

52121

GETA$:REM GET A KE~ FROM THE KE~BOARD

521 IFA$="M"THENPOKEVIC+28,1:REM

MUL TI COLOR

USER SELECTED

52;;:; I FA$=" H" THENPOKEV I C+28., 121 USER SELF;:CTED

HIGH RESOLUTIOt.j

53121 GOT034121

6121121

REM ***** SPRITE DATA *****

61121 DATA64.12I,1,16, 17121,4,6,17121,144,1121,

17121,168,41,105,11214,169,235,11216

170,16121,42,

62121 DATA169,235.11216,169,235,10G,17121,170,170,170,

170,170.170,170,170,170,170,170

63121 DATA166, 17121,154,169,S5, 11216.17121,85, 170,42,170,

168,10,170,160,1,0,64,1,121,64

640 DATA5 ..1;3, 0

PROGRAMMING GRAPHICS

149

OTHER GRAPHICS FEATURES

SCREEN BLANKING

Bit 4 of the VIC-II control register controls the screen blanking function. It is found in the control register at location 53265 ($D011). When it is turned ON (in other words, set to a 1) the screen is normal. When bit 4 is set to 0 (turned OFF), the entire screen changes to border color.

The following POKE blanks the screen.

No data is lost, it just isn't displayed.

"POKE53265,PEEK(53265)AND 239

To bring back the screen, use the POKE shown below:

POKE 53265,PEEK(53265)OR 16

NOTE: Turning off the screen will speed up the processor slightly. This means that program RUNning is also sped up.

RASTER REGISTER

The raster register is found in the VIC-II chip at location 53266

($DOI2). The raster register is a dual purpose register.

When you read this register it returns the lower 8 bits of the current raster position. The raster position of the most significant bit is in register location 53265

($D011). You use the raster register to set up timing changes in your display so that you can get rid of screen flicker. The changes on your screen should be made when the raster is not in the visible display area, which is when your dot positions fall between 51 and 251.

When the raster register is w.ritten to (including the MSB) the number written to is saved for use with the raster compare function. When the actual raster value becomes the same as the number written to the raster register, a bit in the VIC-II chip interrupt register 53273 ($DO19) is turned ON by setting it to 1.

NOTE: If the proper interrupt bit is enabled (turned on), an interrupt (IRQ) will occur.

150 PROGRAMMING GRAPHICS

INTERRUPT

STATUS REGISTER

The interrupt status register shows the current status of any interrupt source. The current status of bit 2 of the interrupt register will be a 1 when two sprites hit each other. The same is true, in a corresponding 1 to 1 relationship, for bits 0-3 listed in the chart below. Bit 7 is also set with aI, whenever an interrupt occurs.

The interrupt status register is located at 53273 ($DOI9) and is as follows:

LATCH

IRST

IMDC

IMMC

ILP

IRQ

BIT # DESCRIPTION

o Set when current raster count

= stored raster count

1 Set by SPRITE-DATAcollision (1st one only, until reset)

2 Set by SPRITE-SPRITEcollision (1st one only, until reset)

3 Set by negative transition of light pen (1 per frame)

7 Set by latch set and enabled

Once an interrupt bit has been set, it's "latched" in and must be cleared by writing a 1 to that bit in the. interrupt register when you're ready to handle it. This allows selective interrupt handling, without having.to store the other interrupt bits.

The INTERRUPTENABLEREGISTERis located at 53274 ($D01A). It has the same format as the interrupt status register.

Unless the corresponding bit in the interrupt enable register is set to aI, no interrupt from that source will take place. The interrupt status register can still be polled for information, but no interrupts will be generated.

To enable an. interrupt request the corresponding interrupt enable bit

(as shown in the chart above) must be set to a 1.

This powerful interrupt structure lets you use split screen modes.

For instance you can have half of the screen bit mapped, half text, more than 8 sprites at a time, etc. The secret is to use interrupts properly.

For example, if you want the top half of the screen to be bit mapped and the bottom to be text, just set the raster compare register (as explained previously) for halfway down the screen. When the interrupt occurs, tell the VIC-II chip to get characters from ROM, then set the raster compare register to interrupt at the top of the screen.

When the interrupt occurs at the top of the screen, tell the VIC-II chip to get characters from RAM

(bit map mode).

PROGRAMMING GRAPHICS

151

You can also display more than 8 sprites in the same way. Unfortunately BASIC isn't fast enough to do this very well. So if you want to start using display interrupts, you should work in machine language.

SUGGESTED

SCREEN AND CHARACTER

COLOR COMBINATIONS

Color TV sets are limited in their ability to place certain colors next to each other on the same line. Certain combinations of screen and character colors produce blurred images.

This chart shows which color combinations to avoid, and which work especially well together.

152

CHARACTER COLOR

a:

6 8 w

(/)

9

10 o

o 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

X

. . .

X

. . . . . .

X X

X X X X

. .

X X X X

. .

X

. .

X

. . .

X X

X X X

. . .

X X X X

X

. .

. . . . .

X

X X X X X X X

X

X X

. .

X X X X

. .

X X X X X X X X X

X X

X

X X X X X X X X X

. . .

X

X X X X X

. . .

X X X X

. . .

X X X

X

. . . .

X X X

X

X X X X X

. .

X

X X

X

X X X X

X X X X X

. .

X

X X X

X X X X

. . . .

X X X

X

X X

X X X X

X X X

. . .

X

. . .

X X

. . . .

X

EXCELLENT

FAIR

POOR

X X X X

. .

X X X X

PROGRAMMING GRAPHICS

PROGRAMMING SPRITES-ANOTHER LOOK

For those of you having trouble with graphics, this section has been designed as a more elementary tutorial approach to sprites.

MAKING SPRITES IN BASIC-A SHORT PROGRAM

There are at least three different BASIC programming techniques which let you create graphic images and cartoon animations on the

Commodore 64. You can use the computer's built-in graphics character

set (see Page

376).

You can program your own characters (see Page

108) or

. . .

best of all

. . .

you can use the computer's built-in "sprite graphics." To illustrate how easy it is, here's one of the shortest spritemaking programs you can write in BASIC:

5(1

AllDramE

PR ItH "6'

POKE2iZ14iZ1.. 13

FOF:::;=8:32TO::::32+62

11,"==5:3248

POKEV+21,l

POKE' +:39.. 1

POKE'v'.' 24

POKE + 1 .' 100

: POKES, 255 : t'~EXT

This program includes the key "ingredients" you need to create any sprite.

The POKE numbers come from the SPRITEMAKINGCHART on

Page 176. This program defines the first sprite

. . .

sprite 0

. . .

as a solid white square on the screen. Here's a line-by-line explanation of the program:

LINE

10 clears the screen.

LINE

20 sets the "sprite pointer" to where the Commodore 64 will read its sprite data from. Sprite 0 is set at 2040, sprite 1 at 2041, sprite

2 at 2042, and so on up to sprite 7 at 2047. You can set all 8 sprite pointers to 13 by using this line in place of line 20:

20 FOR SP=2040T02047:POKE SP,13:NEXT SP

LINE

30 puts the first sprite (sprite 0) into 63 bytes of the Commodore

64's RAM memory starting at location 832 (each sprite requires 63 bytes of memory).

832 to 894.

The first sprite (sprite 0) is "addressed" at memory locations

PROGRAMMING

153

LINE

40 sets the variable "V" equal to 53248, the starting address of the VIDEO CHIP. This entry lets us use the form (V+number) for sprite settings. We're using the form (V+number) when POKEing sprite settings because this format conserves memory and lets us work with smaller numbers.

For example, in line 50 we typed POKE V+21. This is the same as typing POKE 53248+21 or POKE 53269

. . .

but V+21 requires less space than 53269, and is easier to remember.

LINE

50 enables or "turns on" sprite o. There are 8 sprites, numbered from 0 to 7. To turn on an individual sprite, or a combination of sprites, all you have to do is POKE V+21 followed by a number from 0 (turn all sprites off) to 255 (turn all 8 sprites on). You can turn on one or more sprites by POKEing the following numbers:

POKE V+21, 1 turns on sprite O. POKE V+21, 128 turns on sprite 7. You can also turn on combinations of sprites. For example, POKE V+21, 129 turns on both sprite 0 and sprite 7 by adding the two "turn on" numbers

(1+128) together.

(See SPRITEMAKINGCHART, Page 176.)

LINE

60 sets the COLOR of sprite O. There are 16 possible sprite colors, numbered from 0 (black) to 15 (grey). Each sprite requires a different POKE to set its color, from V+39 to V+46.

POKE V+39,1 colors sprite 0 white.

POKE V+46,15 colors sprite 7 grey.

(See the

SPRITEMAKINGCHART for more information.)

When you create a sprite, as you just did, the sprite will STAY IN

MEMORY until you POKE it off, redefine it, or turn off your computer.

This lets you change the color, position and even shape of the sprite in

DIRECTor IMMEDIATEmode, which is useful for editing purposes.

As an example, RUN the program above, then type this line in DIRECTmode

(without a line number) and hit the .:~alll:U.

key:

POKE V+39,8

The sprite on the screen is now ORANGE. Try POKEing some other numbers from 0 to 15 to see the other sprite colors. Because you did this in

DIRECT

mode, if you RUNyour program the sprite will return to its origi-

nal color (white).

154 PROGRAMMING GRAPHICS

LINE 70 determines the HORIZONTALor "X" POSITION of the sprite on the screen.

This number represents the location of the UPPER LEFT

CORNER of the sprite. The farthest left horizontal (X) position which you can see on your television screen is position number 24, although you can move the sprite OFF THE SCREEN to position number O.

LINE 80 determines the VERTICALor "Y" POSITION of thE:'sprite. In this program, we placed the sprite at X (horizontal) position 24, and Y

(vertical) position 100. To try another location, type this POKE in DIRECT mode and hit _t~:llIlt~/_:

POKE

V,24:POKE V+l,50

This places the sprite at the upper left corner of the screen. To move the sprite to the lower left corner, type this:

POKE V,24:POKE V+l,229

Each number from 832 to 895 in our sprite 0 address represents one block of 8 pixels, with three 8-pixel blocks in each horizontal row of the sprite. The loop in line 80 tells the computer to POKE 832,255 which makes the first 8 pixels solid.

. . then POKE 833,255 to make the second

8 pixels solid, and so on to location 894 which is the last group of 8 pixels in the bottom right corner of the sprite. To better see how this works, try typing the following in DIRECT mode, and notice that the second group of 8 pixels is erased:

POKE 833,0 (to put it back type POKE 833,255 or RUN your program)

The following line, which you can add to your program, erases the blocks in the MIDDLEof the sprite you created:

90 FOR A=836 TO 891 STEP 3:POKE A,O:NEXT A

Remember, the pixels that make up the sprite are grouped in blocks of eight. This line erases the 5th group of eight pixels (block 836) and every third block up to block 890. Try POKEing any of the other numbers from

832 to 894 with either a 255 to make them solid or 0 to make them blank.

PROGRAMMING GRAPHICS

155

CRUNCHING YOUR SPRITE PROGRAMS

Here's a helpful "crunching" tip: The program described above is already short, but it can be made even shorter by "crunching" it smaller.

In our example we list the key sprite settings on separate program lines so you can see what's happening in the program.

In actual practice, a good programmer would probably write this program as a TWO LINE

PROGRAM. . . by "crunching" it as follows:

10PRINTCHR$(147):V=53248:POKEV+21, 1:POKE2040, 13:

POKEV+39,1

20FORS =832T0894: POKES,255:NEXT:POKEV,24: POKEY+ 1,100

For more tips on how to crunch your programs so they fit in less memory and run more efficiently, see the "crunching guide" on Page 24.

TV SCREEN

!IA

X POSITION = HORIZONTAL

...J

() a: w

Ci5 a.

A Sprite located here

must

have both its

X-position (horizontal) and V-position (vertical) set so it can be displayed on the screen.

Figure 3-4. The display screen is divided into a grid of X and Y coordinates.

156 PROGRAMMING GRAPHICS

POSITIONING SPRITES ON THE SCREEN

The entire display screen is divided into a grid of X and Y coordinates, like a graph.

The X COORDINATE is the HORIZONTAL position across the screen and the Y COORDINATE is the VERTICALposition up and down (see Figure 3-4).

To position any sprite on the screen, you must POKE TWO SETTINGS

. . .

the X position and the Y position

.. .

these tell the computer where to display the UPPER LEFTHAND CORNER of the sprite. Remember that a sprite consists of 504 individual pixels, 24 across by 21 down.

. . so if you POKE a sprite onto the upper left corner of your screen, the sprite will be displayed as a graphic image 24 pixels ACROSS and 21 pixels

DOWN starting at the X-V position you defined.

The sprite will be displayed based on the upper left corner of the entire sprite, even if you define the sprite using only a small part of the 24X21-pixel sprite area.

To understand how X-Y positioning works, study the following diagram (Figure 3-5), which shows the X and Y numbers in relation to your display screen.

Note that the GREY AREA in the diagram shows your television viewing area

. . .

the white area represents positions which are OFF your viewing screen.

. .

X POSITIONS RUN FROM 0 TO 255,

THEN YOU MUST POKE V+16, 1 255

0-o 24

:~ i

50 -

AND START OVER AT 0 TO 91

:/ x = 24,Y = 50

b'

'J1

255. Y

50 I POKE V+16, 1 AND

231, Y

1 X

65, Y

\ I

:: a:

Zit) a:C\I

(/)0

ZI-

x

24, Y

VIEWINGSCREEN AREA

229 X

229, Y

231 I

~t x

24, Y

250 POKE V+16, 1 AND

= 65,

229

Figure 3-5. Determining X-V sprite. positions.

PROGRAMMING 157

To display a sprite in a given location, you must POKE the X and Y settings for each SPRITE

. . .

remembering that every sprite has its own unique X POKE and Y POKE. The X and Y settings for all 8 sprites are shown here:

POKE THESE VAWES TO SET.X-Y SPRITE POSITIONS

SETX

SPRITEO SPRlTE1 SPRlTE2 SPRlTE3 SPRITE4 SPRITES SPRlTE6 SPRlTE7 v,x

SETY

V+l,Y

V+2,X

V+3,Y

RIGHTX V+16,1

V+16,2

V+4,X

V+S,Y

V+16,4

V+6,X

V+7,Y

V+16,8

V+8,X

V+9,Y

V+10,X V+12,X

V+14,X

V+l1,Y

V+13,Y V+1S,Y

V+16,16 V+16,32

V+16,64 V+16,128

POKEING AN X POSITION: The possible values of X are 0 to 255, counting from left to right. Values 0 to 23 place all or part of the sprite

OUT OF THE VIEWING AREA off the left side of the screen.

. . values 24 to 255 place the sprite IN THE VIEWING AREA up to the 255th position

(see next paragraph for settings beyond the 255th X position). To place the sprite at one of these positions, just type the X-POSITION POKE for the sprite you're using. For example, to POKE sprite 1 at the farthest left

X position IN THE VIEWING AREA, type: POKE V+2,24.

X VALUESBEYOND THE 255TH POSIT10N: To get beyond the 255th position across the screen, you need to make a SECOND POKE using the numbers in the "RIGHT X" row of the chart (Figure 3-5). Normally, the horizontal (X) numbering would continue past the 255th position to 256,

257, etc., but because registers only contain 8 bits we must use a "second register" to access the RIGHT SIDE of the screen and start our X numbering over again at O. So to get beyond X position 255, you must

POKE V+ 16 and a number (depending on the sprite). This gives you 65 additional X positions (renumbered from 0 to 65) in the viewing area on the RIGHT side of the viewing screen.

(You can actually POKE the right side X value as high as 255, which takes you off the right edge of the viewing screen.)

POKEING A Y POSITION: The possible values of Yare 0 to 255, counting from top to bottom. Values 0 to 49 place all or part of the sprite OUT

OF THEVIEWING AREAoff the TOP of the screen. Values 50 to 229 place the sprite IN THE VIEWING AREA. Values 230 to 255 place all or part of the sprite OUT OF THE VIEWING AREA off the BOTTOM of the screen.

158 PROGRAMMING GRAPHICS

let's see how this X-V positioning works, using sprite 1. Type this program:

-'!mil

G!DD

10 PRINT"~~3248:POKEV+21.2:POKE2041.13:

FOP::;=832T0895 :POKES, 255 :t.jE:'<T

20 POKE'

+41;):, 7

3(1 POKEV+2., 24

4(1 POKEV+3, 50

This simple program establishes sprite 1 as a solid box and positions it at the upper left corner of the screen.

Now chclnge line 40 to read:

40 POKE V+3,229

This moves the sprite to the bottom left corner of the screen.

Now let's

test the RIGHT

LIMITof the sprite. Change line 30 as shown:

30 POKE V+2,255

This moves the sprite to the RIGHT but reaches the RIGHT X LIMIT,which is 255. At this point, the "most significant bit" in register 16 must be SET.

In other words, you must type POKE V+16 and the number shown in the

"RIGHT X" column in the X-Y POKE CHART above to RESTARTthe X position counter at the 256th pixel/position on the screen. Change line 30 as follows:

30 POKE V+16, PEEK(V+16)OR 2:POKE V+2,0

POKE

V+ 16,2 sets the most'significant bit of the X position for sprite 1 and restarts it at the 256th pixel/position on the screen.

POKE V+2,O displays the sprite at the NEW POSITION ZERO, which is now reset to the

256th pixel.

To get back to the left side of the screen, you must reset the most

significant

bit of the X position counter to 0 by typing (for sprite 1):

POKE V+16, PEEK(V+16)AND

253

TO SUMMARIZE how theX positioning works

. . .

POKEthe X POSI-

TION for any sprite with a number from 0 to 255. To access a position beyond the 255th position/pixel across the screen, you must use an additional POKE (V+ 16) which sets the most significant bit of the X position and start counting from 0 again at the 256th pixel across the screen.

PROGRAMMING

159

This

'POKEstarts the X numbering over again from 0 at the 256th posi-

tion (Example: POKE V+16, PEEK(V+16)OR 1 and POKE V, 1 must be included to place sprite 0 at the 257th pixel across the screen.) To get back -to the left side X positions you have to

TURN

OFFthe control setting

by typing 'POKE V+'16, PEEK(V+16)AND 254.

POSITIONING MUIIIPLE SPRITES ON THE SCREEN

Here's a program which defines

THREE

:DIFFERENT

2) in different colors .and

places them in different positions .on the screen:

...raI!tJ!n

10 PRI NT":i"~53248

2121FORt1=2040T02042

FORS=.832T0895

: POKES, 255 : t.jEXT

:'POKEM, .13 ::NE:><:T

3(1 POKEV+21.,7

40 POKEV+.39,l: POKEV+4iZ1.,7 :P.OKEV+41, 8

50 POKEV,24:POKEV+l,50

,513 POKEV+2., .12 : POKEV+3., 229

70 POKEV+4,255:POKEV+5,50

For convenience, all 3 sprites have been defined as solid squares, getting their data from. the same place.

The 'important lesson here is how the 3 sprites are positioned.

The white .sprite 0 is ot the. top lefthand corner. The.yellow sprite 1 is at the bottom lefthand corner but'HALF the sprite is OFF THE SCREEN(remember, 24 is the leftmost X position in the viewing area.

. . an X position less than 24 puts 'oll'or part of the sprite

'off the screen and we .used an X position 12 here which put the s.prite

halfway off.the

screen).

Finally, the orange sprite 2 is at the RIGHT X

LIMIT (position 255)

. . .

but what if you want to display a sprite in the

area to .the RIGHT of X position 255?

DISPLAYINGA SPRITE BEYOND THE 255TH X-POSITION

Displaying a sprite beyond the 255th X position requires a special

POKE which SETSthe .most significant 'bit of the X position and starts over at the 256th pixel position across the screen.

Here's how it works.

. .

First, you POKE V+ 16 with the number for :the sprite you're using

(check the

"RIGHT

X" row in the X-Y chart. . . we'll use sprite 0). Now

we assign an X position, keeping in mind that the X counter starts .over

from 0 at the 256th position on the screen.

Change line 50 to read as follows:

50 POKE V+16,1:POKE V,24:POKE V+l,75

1-60 :PROGRAMMING GRAPHICS

This line POKEs V+16 with the number required to "open up" the right side of the screen.

. .the

new X position 24 for sprite 0 now begins 24 pixels to the RIGHT of position 255.

To check the right edge of the screen, change line 60 to:

60 POKE V+16,1:POKE V,65:POKE V+l,75

Some experimentation with the settings in the sprite chart will give you the settings you need to position and move sprites on the left and right sides of the screen.

The section on "moving sprites" will also increase your understanding of how sprite positioning works.

SPRITE PRIORITIES

You can actually make different sprites seem to move IN FRONT OF or

BEHIND each other on the screen. This incredible three dimensional illusion is achieved by the built-in SPRITEPRIORITIESwhich determine which sprites have priority over the others when 2 or more sprites OVERLAPon the screen.

The rule is "first come, first served" which means lower-numbered sprites AUTOMATICALLY sprites. For example, if you display sprite 0 and sprite 1 so they overlap on the screen, sprite 0 will appear to be IN FRONT OF sprite 1. Actually, sprite o always supersedes all the other sprites because it's the lowest numbered sprite. In comparison, sprite 1 has priority over sprites 2-7; sprite

2 has priority over sprites 3-7, etc. Sprite 7 (the last sprite) has LESS

PRIORITYthan any of the other sprites, and will always appear to be displayed

"BEHIND" any other sprites which overlap its position.

To illustrate how priorities work, change lines 50, 60, and 70 in the program above to the following:

P~INT.

I"'~.":I'IM:I

II'

.V-~3,48.FOR~-o~,T089~.POKE~,~~~.NE0T

FORt1=2048T02042

31Z1 POKEV+21,7

POKEV+39,1:POKEV+40,7:POKEV+41,8

5121

POKEV., 24 : POKEV+ 1 , 5121:pm~E',...+16., (I

POKEV+2.34:POKEV+3,60

7121

POKEV+4,44:PC~EV+5,70

You should see a white sprite on top of a yellow sprite on top of an orange sprite. Of course, now that you see how priorities work, you can also MOVE SPRITESand take advantage of these priorities in your animation.

PROGRAMMING GRAPHICS 161

DRAWING A SPRITE

Drawing a Commodore sprite is like coloring the empty spaces in a coloring book. Every sprite consists of tiny dots called pixels. To draw a sprite, all you have to do is "color in" some of the pixels.

Look at the spritemaking grid in Figure 3-6. This is what a blank sprite looks like:

1 6312631

4 2 6 842 1 8 4 2 6 842 1

263 1

8 4 2 6 8 4 2 1

Figure 3-6. Spritemaking grid.

Each little "square" represents one pixel in the sprite. There are 24 pixels across and 21 pixels up and down, or 504 pixels in the entire sprite. To make the sprite look like something, you have to color in these pixels using a special

PROGRAM

. . .

but how can you control over 500 individual pixels? That's where computer programming can help you. Instead of typing 504 separate numbers, you only have to type 63 numbers for each sprite. Here's how it works .

162 PROGRAMMING GRAPHICS

CREATING A SPRITE

. . .

STEP BY STEP

To make this as easy as possible for you, we've put together this simple step by step guide to help you draw your own sprites.

STEP 1:

Write the spritemaking program shown here ON A

PIECE

OF PAPER.

note that line 100 starts a special DATAsection of your program which will contain the 63 numbers you need to create your sprite.

~m:mm

10 PR HIT":1" : POKE53;,80, 5 : POKE53281 , 6

20 V=53248:POKEV+34,3

30 POKE53269,4:POKE2042,13

40 FORH=(;H062: READQ: POKE':'32+t.l.. Q : t.jEXT

2664 32 16 6 4

2 , 12864 32 16' 8 4

100 DATA255,255,255

1'211 DATAI28,0..1

102 DATAI28..0..

103 DRTAI28, 0..1

1(14 DATAI44.0.1-

105 Dt1TI"I144..0..1-

106 DATAI44,0,1-

107 DRTI"I144..0, 1-

108 DATAI44,0,1-

109 DATAI44,O,I-

110 DATAI44,Q,1-

111 DATAI44,0,1-

112 DATAI44,0,1-

113 DATAI44..(I, 1-

114 DATAI28, 0..1-

115 DATAI28, 0..1-

116 DATAI28,O,I-

117 DATA128, 0.. 1-

11:3 DATA128..0..1-

119 DATAI28,0,1-

12121DATA255., 255., 255

:2(10 :.<:=200: 'T'=1(1(1: POKE53252..

:":: POKE53253.. 'r'

2 ,

12864 32 '6 6 4 2 ,

STEP 2:

Color in the pixels on the spritemaking grid on Page 162 (or use a piece of graph paper.

. . remember, a sprite has 24 squares across and 21 squares down). We suggest you use a pencil and draw lightly so you can reuse this grid. You can create any image you like, but for our example we'll draw a simple box.

STEP 3:

look at the first

EIGHT

pixels. Each column of pixels has a number (128,

64, 32, 16, 8, 4, 2, 1). The special type of addition we are going to show you is a type of BINARYARITHMETICwhich is used by most com-

PROGRAMMING GRAPHICS 163

puters as a special way of counting.

Here's a close-up view of the first eight pixels in the top left hand corner of the sprite:

STEP4:

Add up the numbers of the SOLID pixels. This first group of eight pixels is completely solid, so the total number is 255.

STEP 5:

Enter that number as the FIRST DATA STATEMENTin line 100 of the

Spritemaking Program below. Enter 255 for the second and third groups of eight.

STEP6:

Look at the FIRSTEIGHT PIXELSIN THE SECOND ROW of the sprite. Add up the values of the solid pixels. Since only one of these pixels is solid, the total value is 128. Enter this as the first DATAnumber in line 101.

1618

4 2 1

STEP 7:

Add up the values of the next group of eight pixels (which is 0 because they're all BLANK)and enter in line 101. Now move to the next group of

pixels and repeat the process for each GROUPOF

EIGHT

PIXELS(there

are 3 groups across each row, and 21 rows). This will give you a total of

63 numbers.

Each number represents ONE group of 8 pixels, and 63 groups of eight equals 504 total individual pixels. Perhaps a better way of looking at the program is like this

. . .

each line in the program represents ONE ROW in the sprite. Each of the 3 numbers in each row represents ONE GROUP OF EIGHT PIXELS. And each number tells the computer which pixels to make SOLID and which pixels to leave blank.

164 PROGRAMMING

GRAPHICS

STEP 8:

CRUNCH YOUR PROGRAM INTO A SMALLER SPACE BY RUNNING TO-

GETHER ALL THE DATA'STATEMENTS, AS SHOWN IN THE SAMPLE PRO-

GRAM BELOW. Note that we asked you to write your sprite program on a piece of paper.

We did this for a good reason. The DATA STATEMENT

LINES 100- 120 in. the program. in STEP 1 are only thereto help you. see which numbers relate to which 'groups of pixels in your sprite. Your final program should be "crunched" like this:

~S!iImm

1121" :'POI<E53280, 5: POKE53281., 6

2(1 V=5::::24:3: POKEV+34,. 3

30 POKE53269., 4 : POKE2042, 13

4121FOF.:I'I=0T062: READQ : POKE832+t.j, Q : NEi':T

100 DATA255,255,255,128,(I,1,128,0,1,128,O.I,144,(I,

1,144,0,1..144,0,1,144,(1,1

101 DATAL44,0,1,144~0,1,144,O,1,144,e,I,144,0,1,

144, 0., 1 .' 12:::., (I, L 128, 0, 1

11212DI=tTAI28, 10,1.,128.,121,1,128.,.(1,1.,128..

20tt ;<:=200: ITI=100 : POI<E53252., :x:: POKE53253., e.. 1..255..

255, 25~l

IT'

MOVING YOUR SPRITE ON THE SCREEN

Now that you've created your sprite, let's do some interesting things.

with it. To move your sprite: smoothly across the screen, add these two lines' to your program:

50 POKE V+5,100:FOR X=24T0255:POKE V+4,X:NEXT:POKE

V+16,4'

55 FOR X=OT065:POKE V+4,X:NEXT X:POKE V+ 16,0:GOTO 50

LINE 50 POKEs the. Y POSITION at 100 (try

50 or 229 instead for variety). Then it sets up a FOR . . .

NEXT loop which

POKEs the sprite into X position 0 to X position 255, in order.

When it reaches the 255th position, it POKEs the RIGHT X POSITION (POKE V+ 16,4) which is required to'cross to' the riglit.side

of the s<:reen.

LINE55 has a FOR. . . NEXT

loop which continues to POKE the sprite in. the last 65 positions on the screen. Note that the X value was reset to zero but because you. used the RIGHT X setting (POKE

V+ 16,2)

X starts over on the right side of the screen.

This line keeps going back to itself (GOTO 50).. If you just. want the sprite to' move ONCE' across the screen and disappear, then take. out

GOT050.

PROGRAMMING 165.

,Here's a line which moves the sprite BACKAND FORTH:

50 POKE V+5,100:FOR X=24T0255:POKE V+4,X:NEXT:

V+16,4:FOR X=OT065: POKE V+4,X: NEXT X

POKE

55 FOR X=65TOO STEP-l:POKE V+4,X:NEXT:POKE V+16,O: FOR

X=255T024 STEP-l: POKE V+4,X:NEXT

60 GOTO

Do you see how these programs work? This program is the same as the previous one, except when it reaches the end of the right side of the screen, it REVERSES.ITSELFand goes back in the other direction. That is what the STEP-l accomPlishe

. . .

it tells the program to POKE the

sprite into

X values from 65 to 0 on the right side of the screen, then from 255 to 0 on the left sid ~ of the screen, STEPping backwards minus-l position at a time.

VERTICAL SCROLLING

This type of sprite movement called "scrolling." To scroll your sprite up or down in the Y position, 'ou only have to use ONE LINE. ERASE

LINES 50 and 55 by typing t t e line numbers by themselves and hitting .:l:IIII~~I. like this:

50 (

55 (

Now enter LINE 50 again as follOws:

50 POKE V+4,24:FOR Y=OT0I255:POKE V+5,Y:NEXT'

THE

DANCING MOUSE-A SPRITE PROGRAM EXAMPLE

Sometimes the techniques d Cribed in a programmer's reference manual are difficult to understa d, so we've put together a fun sprite program called "Michael's

This program uses three different sprites in a cute animation with sound effects-and to help you understand how it works we've included an explanation of EACH

COMMAND so you can see exactly how the program is constructed:

166 PROGRAMMING GRAPHICS

5 8=54272: POKES+24~, 15: POKES., 22121: POKES+ 1.- 68 : POKES+5,

15:POKES+6,215

1121POKES+7,120:POKES+8,100:POKES+12,15:POKES+13,215

'~III.~.":I.h'JI:I

15 PRIHT":J": V=53248: POKEV+2L 1

2~ZI FORS 1

=

12288TO 1235121 : READQ 1 : POKES 1 , Q1 : HE:":T

25 FORS2= 12352TO 12414 : F.:EAD02 : POKES2., 02 : t.JE:":T

30 FORS3=12416TOI2478:READQ3:POKES3,Q3:HEXT

35 POKEV+39,15:POKEV+l,68

,,&lIB

40 PF.:IHTTAB (16(1) "=11 At-! THE

45 P=192

DAtJC UJO

;6Ia

5121FORX=I2IT0347STEP3

55 RX=INT(X/256):LX=X-RX*256

60 POKE V, U<:: POKEV+ 16, f;:>~

7(1 I FP= 192THE~JG08U:E:200

75 IFP=193THEHGOSUB3121121

8121POKE204e,p:FORT=1T06121:HE>~

:35 P=P+l:IFP>194THENP=192

9121HE:":T

95 EHD

DATi''I:3(1.129., 254., 127.- 129, 254,

127~189~254~127~255J254

101

DATA63,255,252,31,187J248J3,187,192Jl,255J128,

3,189,192,1,231,128,1,255,121

102 DATA31,255,O,0,124,0,0,254,0,1.199.32.3.131.

224,7,1,192.1.192,0,3,192,121

103 DATA30,12I. 12121,63.0,252,127,129,254,127,

127J189J254J127J

255.. 254

129,254

11214 DATA63,255,252,31,221,248,3,221~192,1,255,128,

3J255J192~1}195J128}lJ231J3

105 DATA31)255J255)0)124)0)0)254~0)lJ199J0J7J1J128J

7,0,21214,1.128,124,7,128,56

106 DATA30,0.12121,63~0,252,127,129,254.127,129,254.

127)189)254)127)255)254

107 DATA63,255,252,31,221,248.3,221,192,1,255,134.

108 DATI'=!

255., 22"1., 1 .-252., 0., 3., 254., 0

109 DATA7,14,0,204,14,O,248,56,0,112,112,O,O.60,O.

-1

20121 POKES+4,129:POKES+4, 128:RETURN

31210 POKE8+11 , 129:POKES+l1.

128:RETURN

PROGRAMMING GRAPHICS

167

LINE

5=54272

POKES+24, 15'

POKES,220

POKES+ 1,68

POKES+5,15

POKES+6~215

Sets the variable 5 equal to 54272, which is the beginning memory location of the SOUND CH1P.

From now on, instead of poking a direct memory location, we will POKE 5 plus a value..

Same, as POKE '54296,1-5 which sets VOLUME'to highest leveL.

Same

as POKE- 54272,220 which sets Low Frequency in Voice 1"for a note which approximates' high'C in Octave' 6.

Same as POKE.54273~68' which sets High Fre'" quencyin Voice 1 for a. note: which approximates high- C. in Octave 6;

Same as POKE 54277,15 which sets Attack/Decay for Voice 1 and; in thi~ 'case co,nsists of the maximum DECAYlevel' with no attack, which' pro'" .

duces the "echo"'effect.

Same as POKE 54278,21S'which sets' Sustain/ Release. for Voice 1 (21"5 represents a combination of sustain and release values). .

LINE' 10:

POKES+7,120

POKES+8,100

POKES+12,15

POKES'+13,2l5

Same as POKE 54279, 120'which sets the-Low Frequency for Voice 2.

Same as POKE 54280,100 which se1s the High

Frequency' for Voice .2.

Same as POKE 54284,15 which sets Attack/Decay for Voice 2 to same level .as Voice 1 above.

Same' as POKE 54285;215,which sets Sustain/ Release for Voice 2 to same level as Voice 1 above.

LINE 15:

PRINT"

1...~.j:I.]fll:l

Emil'

V=53248

Clears the screen when the program begins.

Defines the variable "v" as the starting location of the VIC chip which controls sprites.

From now on we will define sprite locations as V plus a value.

Turns on (enables)' sprite number 1.

168

POKfV+2l,1

PROGRAMMING GRAPHICS

LINE

20:

FORS

1 = 12288

TO 12350

READ Q 1

POKES1,Q1

We are going to use ONE SPRITE(sprite 0) in this animation, but we are going to use THREEsets of sprite data to define three separate shapes.

To get our animation, we will switch the POINTERS for sprite ° to the three places in memory where we have stored the data which defines our three different shapes.

The same sprite will be redefined rapidly over and over again as 3 different shapes to produce the dancing mouse animation.

You can define dozens of sprite shapes in DATA

STATEMENTS,and rotate those shapes through one or more sprites. So you see, you don't have to limit one sprite to one shape or vice-versa.

One sprite can have many different shapes, simply by changing the POINTER SETTING FOR THAT

SPRITE to different places in memory where the sprite data for different shapes is stored.

This line means we have put the DATA for "sprite shape 1" at memory locations 12288 to 12350.

Reads 63 numbers in order from the DATAstatements which begin at line 100. Q1 is an arbitrary variable name. It could just as easily be A, Z1 or another numeric variable.

Pokes the first number from the DATA statements

(the first "Q1" is 30) into the first memory location

(the first memory location is 12288). This is the same as POKE12288,30.

This tells the computer to look BETWEENthe FOR and NEXT parts of the loop and perform those in-between commands (READQ1 and POKES1,Q1 using the NEXTnumbers in order). In other words, the NEXTstatement makes the computer READthe

NEXTQ1 from the DATASTATEMENTS,which is 0, and also increments S1 by 1 to the next value,

which is

12289.

The result is POKE12289,0

. . .

the NEXT command makes the loop keep going back until the last values in the series, which are

POKE 12350,0.

PROGRAMMING 169

LINE

25:

FORS2

12352

TO 12414

READQ2

POKES2,Q2

LINE

30:

FORS3= 12416

TO 12478

READQ3

POKES3,Q3

LINE

35:

POKEV+39,15

POKEV+ 1,68

The second shape of sprite zero is defined by the

DATA which is located at locations 12352 to

12414. NOTE that location 12351 is SKIPPED. . .

this is the 64th location which is used in the definition of the first sprite group but does not contain any of the sprite data numbers. Just remember when defining sprites in consecutive locations that you will use 64 locations, but only

POKE sprite data into the first 63 locations.

Reads the 63 numbers which follow the numbers we used for the first sprite shape.

This READsimply looks for the very next number in the DATA area and starts reading 63 numbers, one at a time.

Pokes the data (Q2) into the memory locations

(52) for our second sprite shape, which begins at location 12352.

Same use as line 20 above.

The third shape of sprite zero is defined by the

DATAto be located at locations 12416 to 12478.

Reads last 63 numbers in order as Q3.

Pokes those numbers into locations 12416 to

12478.

Same as lines 20 and 25.

Sets color for sprite 0 to light grey.

Sets the upper right hand corner of the sprite square to vertical (Y) position 68. For the sake of comparison, position 50 is the top lefthand corner

Y position on the viewing screen.

170 PROGRAMMING GRAPHICS

LINE

40:

PRINTTAB(160)

Tabs 160 spaces from the top lefthand CHAR-

ACTERSPACE on the screen, which is the same as

4 rows beneath the clear command.

. . this starts your PRINT message on the 6th line down on the screen.

Hold down the marked

B8 key and press the key

11II at the same time. If you do this inside quotation marks, a "reversed E" will appear.

This sets the color to everything PRINTed from then on to WHITE.

This is a simple PRINT statement.

I AM THE

DANCING

MOUSE!

mil"

This sets the color back to light blue when the

PRINT statement ends. Holding down m and

II at the same time inside quotation marks causes a "reversed diamond symbol" to appear.

LINE

45:

P= 192

Sets the variable P equal to 192. This number 192 is the pointer you must use, in this case to "point" sprite 0 to the memory locations that begin at location 12288. Changing this pointer to the locations of the other two sprite shapes is the secret of using one sprite to create an animation that is actually three different shapes.

LINE

50:

FORX=OT0347

STEP3

Steps the movement of your sprite 3 X positions at a time (to provide fast movement) from position 0 to position 347.

PROGRAMMING GRAPHICS 171

LINE

55:

RX=INT(X/256)

LX=X-RX*256

RX is the integer of X/256 which means that RX is rounded off to 0 when X is less than 256, and RX becomes 1 when X reaches position 256. We will use RX in a moment to POKE V+16 with a 0 or 1 to turn on the "RIGHT SIDE" of the screen.

When the sprite is at X position 0, the formula looks like this: LX

(0 times 256) or o. When the sprite is at X position 1 the formula looks like this: LX

(0 times 256) or 1. When the sprite is at X position 256 the formula looks like this: LX

256

(1 times 256) or 0 which resets X back to o which must be done when you start over on the

RIGHT

SIDEof the screen (POKEV+16,1).

LINE

60:

POKEV,LX

POKEV+16,RX

You POKE V by itself with a value to set the Horizontal (X) Position of sprite 0 on the screen. (See

SPRITEMAKING CHART on Page 176). As shown above, the value of LX, which is the horizontal position of the sprite, changes from 0 to 255 and when it reaches 255 it automatically resets back to zero because of the LXequation set up in line

55.

POKEV+16 always turns on the "right side" of the screen beyond position 256, and resets the horizontal positioning coordinates to zero. RX is either a 0 or a 1 based on the position of the sprite as determined by the RXformula in line 55.

LINE

70:

IFP= 192THEN

GOSUB200

If the sprite pointer is set to 192 (the first sprite shape) the waveform control for the first sound effect is set to 129 and 128 per line 200.

172 PROGRAMMING GRAPHICS

LINE

75:

IFP=193THEN

GOSUB300

If the sprite pointer is set to '193 (the second sprite shape) the waveform control for the second sound effect (Voice 2) is set to 129 and 128 per line 300.

UNE 80:

POKE2040,P

FORT= lT060:

Sets the SPRITE POINTER to location 1-92 (re-

member P=192 in line

451 Here's where we use the P).

A simple time delay loop which sets the speed at

.which the mouse dances.

(Try a faster or slower speed by increasing/decreasing the number t>0.)

LINE 85:

P=P+1

IFP>194THEN

P= 192

Nowwe increase the value,of the pointer by adding 1 'to the original value ofP.

We only w.ant to point the sprite YO3 memory locations.

'192 points to locations 1"2288 to ,12350,

193 points to locatio'ns 12352 to 12414, and 194 points to locations 12416 to 12478. This line tells the computer to reset P back to 192 as ,soon as P becomes 195 so P never really becomes 195. P is

192, '193, 194 and then resets back to 192 and the pointer winds up pointing consecutively to the three sprite shapes in the three 64-byte groups of memory locations containing the' DATA.

PROGRAMMING GRAPHICS

173

LINE

90:

N EXTX

After the sprite has become one of the 3 different shapes defined by the DATA, only then is it allowed to move across the screen. It will jump

X positions at a time (instead of scrolling smoothly one position at a time, which is also possible).

STEPping

3 positions at a time makes the mouse

"dance" faster across the screen. NEXTX matches the FOR. . . X position loop. in line 50.

LINE 95

END

LINES

100-109

DATA

ENDs the program, moves off the screen.

which occurs when the sprite

The sprite shapes are read from the data numbers, in order.

First the 63 numbers which comprise sprite shape 1 are read, then the 63 numbers for sprite shape 2, and then sprite shape 3.

This data is permanently read into the.3 memory locations and after it is read into these locations, all the program has to do is point sprite 0 at the

3 memory locations and the sprite automatically takes the shape of the data in those locations.

We are pointing the sprite at 3 locations one at a time which produces the "animation" effect.

If you want to see how these numbers affect each sprite, try changing the first 3 numbers in liNE

100 to 255, 255, 255. See the section on defining sprite shapes for more information.

174 PROGRAMMING GRAPHICS

LINE

200:

POKES+4,129

POKES+4,128

RETURN

Waveform control set to 129 turns on the sound effect

Waveform control set to 128 turns off the sound effect

Sends program back to end of line 70 after waveform control settings are changed, to resume program.

LINE

300:

POKES+11,129

POKES+ll,128

RETURN

Waveform control set to 129 turns on the sound" effect

Waveform control set to 128 turns off the sound effect

Sends program back to end of line 75"to resume.

PROGRAMMING GRAPHICS 175

EASY SPR1TEMAKING CHART

SPRITE SPRITE SPRITE SPRITE

SPRITE

0 1 2 3 ..

SPRITE

Turn on Sprite

Put in.Memory

(Set Pointers)

Locations for

Sprite Pixel

(12288-12798)

Set Priority of Sprites

V+21,r

2040,

192

12288.

12350

V+21,2

2041,

193

12352 to

12414'

V+21,4

2042,

194

12416 to

1247.8

V+21,8

2043,

195

12480.

12542

V+21,16 V+21,32

V+21,64 V+21,128

2044,

196

12544 to

12606

2045,

197

12608 to

12670

2046,

198

12672.

12734

2047,

199

12736 to

12798

Sprite Color

Set LEFTX

Position (0-255)

V+39,C

V+O,X

V+40,C

V+2,X

V+41,C

V+4,X

V+42,C

V+6,X

.V+43,C

V+8,X

V+44,C

V+10,X

V+45,C

V+12,X

V+46,C

V+14,X

Set RIGHT X

V+16,1.

V+16,2

Position. (0- 255)

V+O,X V+2,X

Set Y Position

V+I,Y V+3,Y

V+16,4

V+4,X'

V+16,8

V+6,X

V+16,16

V+8,X

V+16,32

V+10,X

V+16,64

V+12,X

V+16,128

V+14,X

V+5,Y V+7;Y.

V+9,Y V+I1,Y V+13,Y V+15,Y

V+29,16 V+29,32

V+29,64

V+29,128

Expand Sprite

Horizontally/)(

Multi-Color 2

(Second Color)

V+29,1

V+29,2 V+29,4

Expand Sprite

Vertica lIylY

Tum On (Set)

Multi-Color Mode

V+28,1

Multi-Color 1

(First Color)

V+23',1

V+37,C

V+23,2

V+28,2

V+37,C

V+23.4

V+28;4

V+37;C

V+29,8

V+23,8

V+28,8

V+37,C

V+23,16

V+28,16

V+37,C.

V+23,32

V+28,32

V+37,C

V+38;C V+38,C

V+38,C V+38,C V+38,C V+38,C

V+23,64

V+28,64

V+37,C

V+38,C

V+23,128

V+28,128

V+37,C'

V+38,C

The rule is that lower numbered '.sprites always have display priority over higher

numbered sprites.

For example, sprite'O has priority over ALLother sprites, sprite

7 has last priority. This means lower numbered sprites always appearto move

IN FRONT OF or ON TOP OF higher numbered sprites.

Collision (Sprite to Sprite)

Collision (Sprite to Background)

V+30

V+31

IF PEEK(V+30)ANDX=X THEN

[action]

IF PEEK(V+31)ANDX=X THEN [action]"

176 PROGRAMMING' GRAPHICS

SPRITEMAKING NOTES

Alternative Sprite Memory Pointers and Memory Locations

Using Cassette Buffer

Put in Memory

(Set pointers)

Sprite Pixel

Locations for

Blocks 13-15

SPRITE 0

2040,13

832 to 894

SPRITE 1

2041,14

896 to 958

SPRITE 2

2042,15

960 to 1022

If you're using 1 to 3 sprites you can use these memory locations in the cassette buffer (832 to 1023) but for more than 3 sprites we suggest using locations from

12288 to 12798 (see chart).

TURNING ON SPRITES:

You can turn on any individual sprite by using POKE V+21 and the number from the chart.

. . BUT. . . turning on just ONE sprite will turn

OFF any others. To turn on TWO OR MORE sprites, ADD TOGETHERthe numbers of the sprites you want to turn on (Example: POKE V+21, 6 turns on sprites 1 and 2). Here is a method you can use to turn one sprite off and on without affecting any of the others (useful for animation).

EXAMPLE:

To turn off just sprite 0 type: POKE V+21,PEEK V+21AND(255-l).

Change the number 1 in (255-1) to 1,2,4,8,16,32,64, or 128 (for sprites

0-7).

To re-enable the sprite and not affect the other sprites currently turned on, POKE V+21, PEEK(V+2l)OR 1 and change the OR 1 to OR 2

(sprite 2), OR 4 (sprite 3), etc.

X POSITION VALUESBEYOND 255:

X positions run from 0 to 255

. . .

and then STARTOVER from 0 to

255. To put a sprite beyond X position 255 on the far right side of the screen, you must first POKE V+ 16 as shown, THEN POKE a new X value from 0 to 63, which will place the sprite in one of the X positions at the right side of the screen. To get back to positions 0-255, POKE V+16,0 and POKE in an X value from 0 to 255.

Y POSITION VALUES:

Y positions run from 0 to 255, including 0 to 49 off the TOP of the viewing area, 50 to 229 IN the viewing area, and 230 to 255 off the

BOTTOM of the viewing area.

PROGRAMMING 177

SPRITE

COLORS:

To make sprite 0 WHITE, type: POKE V+39,1 (use COLOR POKE SET-

TING shown in chart, and INDIVIDUALCOLOR CODES shown below):

0BLACK

1-WHITE

2-RED

3-CYAN

MEMORY LOCATION:

4-PURPLE

5-GREEN

6-BLUE

7 YELLOW

8-0RANGE

9-BROWN

10-LT.

RED

12-MED.

GREY

13-LT.

GREEN

14-LT.

BLUE ll-DARK GREY 15-LT.

GREY

You must "reserve" a separate 64-BYTE BLOCK of numbers in the computer's memory for each sprite of which 63 BYTESwill be used for sprite data.

The memory settings shown below are recommended for the "sprite pointer" settings in the chart above.

Each sprite will be unique and you'll have to define it as you wish. To make "all sprites exactly the same, point the sprites you want to look the same to the same register for sprites.

DIFFERENT SPRITE POINTER SETTINGS:

These sprite pointer settings are RECOMMENDATIONSONLY.

Caution: you can set your sprite pointers anywhere in RAM memory but if you set them too "low" in memory a long BASIC program may overwrite your sprite data, or vice versa. To protect an especially LONG

BASIC PROGRAM from overwriting sprite data, you may want to set the sprites at a higher area of memory (for example, 2040,192 for sprite 0 at locations 12288 to 12350

. . .

2041,193 at locations 12352 to 12414 for sprite 1 and so on . . . by adjusting the memory locations from which sprites get their "data," you can define as many as 64 different sprites plus a sizable BASIC program.

To do this, define several sprite "shapes" in your DATAstatements and then redefine a particular sprite by changing the "pointer" so the sprite you are using is "pointed" at different areas of memory containing different sprite picture data.

See the "Dancing Mouse" to see how this works. If you want two or more sprites to have THE SAME SHAPE (you can still change position and color of each sprite), use the same sprite pointer and memory location for the sprites you want to match (for example, you can point sprites 0 and 1 to the same location by using POKE 2040,192 and POKE 2041, 192).

178 PROGRAMMING GRAPHICS

PRIORITY:

Priority means one sprite will appear to move "in front of" or "behind" another sprite on the display screen.

Sprites with more priority always appear to move "in front of" or "on top of" sprites with less priority.

The rule is that lower numbered sprites have priority over higher numbered sprites.

Sprite 0 has priority over all other sprites.

Sprite 7 has no priority in relation to the other sprites.

Sprite 1 has priority over sprites 2-7,

etc.

If you put two sprites in the same position, the sprite with the higher priority will appear

IN FRONT OF the sprite with the lower priority. The sprite with lower priority will either be obscured, or will "show through"

(from "behind") the sprite with higher priority.

USING MULTI-COLOR:

You can create multi-colored sprites although using multi-color mode requires that you use PAIRSof pixels instead of individual pixels in your sprite picture (in other words each colored "dot" or "block" in the sprite will consist of two pixels side by side). You have 4 colors to choose from:

Sprite Color (chart above), Multi-Color I, Multi-Color 2 and "Background

Color" (background is achieved by using zero settings which let the background color "show through").

Consider one horizontal 8-pixel block

in a sprite picture. The color of each

PAIR

of pixels is determined accord-

ing to whether the left, right, or both pixels are solid, like this:

BACKGROUND (Making

BOTH PIXELS BLANK (zero) lets the

INNER SCREEN

COLOR (background) show through.)

MULTI-COLOR

1 (Making the RIGHT PIXEL SOLID in a pair of pixels sets

BOTH PIXELS to Multi-Color 1.)

SPRITE COLOR

(Making the LEFT

PIXEL SOLID in a pair of pixels sets

BOTH PIXELS to Sprite Color.)

MULTI-COLOR

2 (Making BOTH PIXELS SOLID in a pair of pixels sets

BOTH PIXELS to Multi-Color 2.)

PROGRAMMING GRAPHICS 179

Look

at the horizontal 8-pixel row shown below. This block sets the

first two pixels to background color, the second two pixels to Multi-Color

1, the third two pixels to Sprite Color and the fourth two pixels to Multi-

Color 2. The color of each

PAIR

of pixels depends on which bits in

each pair are solid and which are blank, according to the illustration above. After you determine which colors you want in each pair of pixels, the next step is to add the values of the solid pixels in the 8-pixel block, and POKE that number into the proper memory location. For example, if the 8-pixel row shown below is the first block in a sprite which begins at memory location 832, the value of the solid pixels is 16+8+2+1

= 27, so you would POKE 832,27.

, 16 + 8 + 2 + l'

COLLISION:

You can detect whether a sprite has collided with another sprite by using this line: IF PEEK(V+30)ANDX=XTHEN [insert action here]. This line

checks to see if a particular sprite has collided with

ANY OTHER

SPRITE,

where X equals 1 for sprite 0, 2 for sprite 1, 4 for sprite 2, 8 for sprite 3,

16 for sprite 4, 32 for sprite 5, 64 for sprite 6, and 128 for sprite 7. To check to see if the sprite has collided with a "BACKGROUND

CHAR-

ACTER" use this line: IF PEEK(V+3l)ANDX=XTHEN [insert action here].

180

PROGRAMMING GRAPHICS

USING GRAPHIC CHARACTERS IN DATA STATEMENTS

The following program allows you to .create Q.sprite using blanks and solid circles ( ').in DATA statements.

The spr~te:and the numbers. POKEd .into the sprite data registers are displayed.

.:-BllilCIIiIII

18 PR!NT" ~ :FiJRI =8T063 : POKE832+ I .' 8 : HE)<:T

:;-~8 GOSU:E:6iZ1000

.999

Et.m

DATA".......

613001 IIATA"

DATA"

GI "

,Ii.

6130103 DATA" 811I1111I'11I110

6012ltNDATI=t" .'IIII.iP8

613£11215DATA"

... .....

6013iZI6DATA" '1lilDiP

DATA"

60808 DATA"...Ci.............

....

.....

6(18£19

DA'TA

1121IIATA"

"..............

612112111DATA"

68tH

60813DATA"GI

613014DATA"

60015 DATA"

68016 DATA"

613817DATA"

601318DfiTI"i"

68819 DATA"

,...

011I .

II ..

..

.....

...

.

601£1(1 '11=53248: POKEV, 21313:POKEV+1.. 10121:POKEV+21, 1 :

POKEV+39,14:POKE2848,13

6~U 1215F.'OKE'y'+23, 1 : POKEV+29, 1

6121110 FOR I =(1T020 :.READA$ : FORK=0T02 : T=13: FOF:J=1<n07 : B=13

612114121IFtlID$(,A$..

J+K:+:8+1.. 1 )="."THEHB=l

6015121 T=T+B*2'f'(7-~T): HEXT: PRIHTT.; : POKE832+I*:;:HK, T:

NE:>::T : PFH t-n : t'IE>':T

612121210 RETUR:t.1

PROGRAMMING GRAPHICS .181

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Key features

Text display
High resolution display
Sprites
Programmable characters
Multi-color mode graphics
Extended background color mode
Bit mapped graphics
Multi-color bit map mode
Smooth scrolling

Frequently asked questions

Set bit 4 of the VIC-II control register at 53270 ($D016) to a 1 by using the following POKE: POKE 53270,PEEK(53270)OR 16

Set bit 4 of location 53270 to a 0 by the following POKE: POKE 53270,PEEK(53270)AND 239

POKE a number into color memory. POKEing a number from 0 to 7 gives the normal character colors. POKEing a number between 8 and 15 puts the space into multi-color mode.

320 horizontal dot by 200 vertical dot resolution

Set bit 5 of the VIC-II control register to a 1 at location 53265 ($DOll in HEX). The following POKE will do this: POKE 53265,PEEK(53265)OR 32

Set bit 5 of the VIC-II control register to 0 at location 53265 ($DOll), like this: POKE 53265,PEEK(53265)AND 223

You must clear out the section of memory that you're using for your programmable characters. Use a loop to POKE 0 to every memory location in that range.

GRAPHICS OVERVIEW

A) CHARACTER DISPLAYMODES

1) Standard Character Mode

2) Multi-Color Character Mode

3) Extended Background Color Mode

B) BIT MAP MODES

1) Standard Bit Map Mode

2) Multi-Color Bit Map Mode

1) Standard Sprites

2) Multi-Color Sprites

GRAPHICS LOCATIONS

VIDEO BANK SELECTION

chip can "see" the entire 64K of memory. The BANK

bits that

SCREEN MEMORY

COLOR MEMORY

Color memory can NOT move. It is always located at locations

through

Screen memory (the 1000 locations

appears in the corresponding RAM at locations

STANDARD CHARACTER MODE

CHARACTER DEFINITIONS

PROGRAMMABLE CHARACTERS

5 PRINTCHR$(142)

:REM SWITCH TO

KEYSCAN INTERRUPTTIMER

30 POKE1,PEEK(1)AND251 :REM SWITCH IN

stored as a group of eight bytes.

patterns of the bytes directly

characters,

NEWand then type this program:

Figure 3-1. Programmable Character Worksheet.

10 REM* EXAMPLE1 *

MULTI-COLOR MODE GRAPHICS

MULTI-COLOR MODE

SET BACKGROUND

COLOR

DO ALL 8

EXTENDED BACKGROUND COLOR MODE

BIT MAPPED GRAPHICS

STANDARD HIGH-RESOLUTION BIT MAP MODE

HOW IT WORKS

If you remember the

CHARACTERS

MAP

Zo

=;3

°3

. . . . . . . . .

639

BASE+ ROW*320+ CHAR*8+ LINE

MULTI-COLOR

BIT MAP MODE

1/2 byte

SMOOTH SCROLLING

chip supports smooth scrolling in both the horizontal and

PRItH

HELLO

;

SPRITES

DEFINING A SPRITE

..,

POINTERS

TURNING SPRITES ON

TURNING SPRITES OFF

MULTI-COLOR MODE

SEnlNG

A

SPRITE TO MULTI-COLORMODE

does this:

EXPANDED

the VIC-II control register at location

D in HEX)must be turned

(set to a 1). The following

expands a sprite in the X

POSITIONING

POKE

HEX

1121 -

SET

BASE+ ROW320+ CHAR8+ LINE