Commodore 64 Uživatelský manuál stáhnout pdf (Strana 74)

LINE 55:

RX=INT(X/256)

LX=X-RX*256

LINE 60:

POKEV,LX

POKEV+16,RX

LINE 70:

IFP= 192THEN

GOSUB200

RXis the integer of X/256 which means that RXis

rounded off to 0 when X is less than 256, and RX

becomes 1 when X reaches position 256. We will

use RXin 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 - (0 times 256) or o. When

the sprite is at X position 1 the formula looks like

this: LX

= 1 - (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).

You POKE V by itself with a value to set the Hori-

zontal (X) Position of sprite 0 on the screen. (See

SPRITEMAKINGCHART 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.

If the sprite pointer is set to 192 (the first sprite

shape) the waveform control for the first sound ef-

fect is set to 129 and 128 per line 200.

172 PROGRAMMING GRAPHICS

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Commodore 64 Uživatelský manuál Strana 74