Commodore VIC-20 User Manual page 199

60050 IF SC(160 THEN SC=128:RETURN
60060 IF SC(192 THEN SC=SC-64:RETURN
60070 IF SC(255 THEN SC=SC-128:RETURN
60~80
SC-94:RETURN
Moving Dot Revisited
Chapter 6: Graphics
185
In Chapter 5 we presented a program that moved a dot around the
screen as an example of using the joystick. Here, for comparison, is how that
program could be written using POKE instead of PRINT. As before, this
program is not complete: You must add the appropriate subroutine to use
either the keyboard or the joystick for control.
100 REM CLEAR SCREEN
110 PRINT":'lI"
120 REM SET COLOR MEMORY
130 CB=37888+256*<PEEK(648) AND 2)
140 FOR I=CB TO CB+505
150 POKE 1,6
160 NEXT I
170 ){P=0:YP=0
180 SB=PEEK(648)*256
190 REM MAIN LOOP
290 GOSUB 63000
210 IF (XI-0) AND (YI=0) RND (FB=0) THEN 200
220 REM ERASE OLD DOT
230 POKE SB+XP+22*YP,32
240 REM CALCULATE NEW X POSTION
250 XP=XP+XI
260 IF XP)21 THEN XP=0
270 IF XP(0 THEN XP=21
280 REM CALCULATE NEW Y POSTION
290 YP=YP+YI
300 IF YP)22 THEN YP=0
310 IF YP(0 THEN YP=22
320 REM POKE NEW DOT
330 POKE SB+XP+22*YP,Sl
340 GOTO 200
ANIMATING YOUR PLAYERS
There are two facets to player animation. The first we have already
discussed: moving a player around on the screen. The second involves
changing the player itself so that it appears to be doing something. To
animate a player, one or more of the characters that make it up are changed,