Commodore 64 Uživatelský manuál stáhnout pdf (Strana 41)

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~

1121PRnn":T - :REt'1 CLEAF.: SCF.:EEt,1

20 POKE2040 , 13 :REM GET SPRITE 0

DATA FROM BLOCK 13

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

DATA INTO BLOCK 13 (13*64=832)

40 V=53248 :REM SET BEGINNING

OF VIDEO CHIP

5121POKEV+21" 1 :F.'Et1 EI"IABLE ~;PRITE

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

COLOR

71<:1POKE '+ 1 " 11210

'T' POSITIO~I

80 POKEV+16,0:POKEV,100

>': POSITION

: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 neces-

sary a sprite now has 512 possible positions in the left/right, X, direc-

tion. 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 SIGNIFICANTBITPOSITION register

must be set to a 1 (turned ON). If the X position of a sprite is less than

PROGRAMMINGGRAPHICS 139

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 82 83

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