Commodore VIC-20 User Manual page 227

10 POKE 7432,PEEK(7432) AND
M0~(3)
20 POKE 7432,PEEK(7432) OR Mlr.(3)
Chapter 6: Graphics
213
Even with techniques like precalculating masks, BASIC is usually too
slow for animation of high-resolution displays; there are just too many bits
'to be changed in order to move a player around the screen. This kind of
high-speed "bit juggling" is best done in machine language. BASIC is,
however, quite useful for displays that don't move, such as drawings and
graphs. For example; the following program will draw a triangle on the
screen:
100 REM PROTECT CHARACTER MEMORY
110 POKE 52,24: POKE 56,24: CLR
120 POKE 36869,254
130 REM COPY UNREVERSEDCHARACTERS
140 FOR 1-6144 TO 7167 : POKE I,PEEK(26624+I) NEXT
150 REM CLEAR CUSTOM CHARACTERS
160 FOR 1=7168 TO 7679 : POKE I,e : NEXT
170 REM BUILD HI-RES WORK AREA
180 PRINT ":'lIDHPX (08"
190 PRINT "IIFIIQY! >19"
200 PRINT "IIlBJRZ"; CHR$(34); CHR$(34); CHR$(20); "*2: "
210 PRINT "Il:KS[I+3i"
220 PRINT "alDL T£S, 4("
230 PRINT "IIEMUJ~-5-"
240 PRINT "FNVt&.6)"
250 PRINT "130W+-'
In"
260 REM BUILD MASK ARRAY
270 FOR 1-0 TO
7:Ml~(I)=2tI
: NEXT I
290 REM DRAW BOTTOM OF TRIANGLE
290 Y-63
300 FOR X-0 TO 63
310 OOSUB 450
320 NEXT
330 REM DRAW LEFT SIDE OF TRIANGLE
340 FOR X=0 TO 30
350 Y
=
63-XIII2'
360 OOSUB 450
370 NEXT
380 REM DRAW RIGHT SIDE OF TRIANGLE
390 FOR X-31 TO 62
400 Y - 63-(62-X)1IE2
410 OOSUB 450
420 NEXT
430 END
440 REM BIT SETTING SUBROUTINE
450 COL-INT(X/8)
460 Pl-7168+Y+64*COL