0 REM << RR18-1 >>
1 REM
2 REM     RUPERT REPORT #18
3 REM     LISTING
4 REM     BIT MAP GRAPHICS
5 REM
10 DEF FNSB(N)=PEEK(MM) OR 2^N
20 DEF FNRB(N)=PEEK(MM) AND (255-2^N)
30 VV=53248 :REM VIC-II REGISTER 0
35 :REM >>> PUT BIT MAP AT 8192 <<<         (SET BIT 3 OF VIC REGISTER 24)
40 MM=VV+24 : POKE MM,FNSB(3)
45 :REM >>> SELECT BIT MAP MODE <<<         (SET BIT 5 OF VIC REGISTER 17)
50 MM=VV+17 : POKE MM,FNSB(5)
60 BASE=8192 :REM START BIT MAP MEMORY
65 :REM >>> CLEAR BIT MAP <<<
70 FOR MM=BASE TO BASE+7999
80 POKE MM,0 : NEXT MM
85 :REM >>> SELECT COLORS C1 AND C0 <<<
90 C1=1 : C0=0 : CC=16*C1 + C0
95 :REM >>FILL SCREEN MEMORY WITH COLOR
100 FOR MM=1024 TO 2023:POKE MM,CC:NEXT
194 :
195 ::REM:: MAIN PROGRAM ::
196 :
200 FOR N=1 TO 1000
210 X=RND(0)*320 : Y=RND(0)*200
220 GOSUB 400 : NEXT
250 FOR P=1 TO 3000 : NEXT
294 :
296 :
300 :REM >>> RESET BIT MAP MODE <<<
310 MM=VV+17 : POKE MM,FNRB(5)
320 :REM >>> RESTORE SCREEN MEMORY BASE
330 MM=VV+24 : POKE MM,FNRB(3)
390 END
395 :REM >>> TURN ON PIXEL AT (X,Y)
400 BIT=7-(X AND 7)
410 MM=BASE+320*INT(Y/8)+8*INT(X/8)+(Y AND 7)
420 POKE MM,FNSB(BIT)
430 RETURN