williams-et-al-1983-apple-ii-computer-graphics

CHAPTER 8-Hl-RES GRAPHICS 75The row and column addresses depend on which box you will use toplot the alien, but the address for the position in the box is fixed by therow's position in the figure. The position address for row one is © ($©), forrow two it is 1©24 ($4©©), fo r row three it is 2©48 ($8©©), and so forth, asshown in the Hi-Res memory map (see Figure 8-3). The following programtakes advantage of those facts as it plots the alien in any box you chooseon the mixed mode Hi-Res screen.1 REM ALIEN PLOT2 REM3 REM INITIALIZATION4 DIM RA% (2)5 FOR I = 1 TO 2 : READ RA%(I) :NEXT I6 REM7 REM INPUT ROW AND COLUMN8 HGR : HOME : VTAB (24)9 INPUT "ROW NUMBER? (1-2) ";R$1 R% = VAL (R$)11 IF .t:t/0 < 1 OR R% > 2 THEN PRINTCHR$ (7) : GOTO 912 INPUT "COLUMN NUMBER? (1-4)";C$13 C% = VAL (C$)14 IF C% < 1 OR C% > 4 THEN PRINTCHR$ (7) : GOTO 1215 BA% = RA% (R%) + C%-116 POKE BA%,2817 POKE BA% + 124, 6218 POKE BA% + 248, 7319 POKE BA% + 372, 732 POKE BA% + 496, 6221 POKE BA% + 512, 2822 POKE BA% + 6144, 3423 POKE BA% + 7168,6524 REM25 PRINT "PLOT ANOTHER? (Y/N) ": GET A$26 IF A$ < > "N" GOTO 927 TEXT : HOME28 END29 DATA 8192,832, 8448,8576, 874,8832,896,988,8232, 8363 DATA 8488,8616,8744,8872,9'9128, 8272,84,8528, 8656Listing 8-2. Alien plot.Lines 4© through 6© dimension and initialize an array containing thetwenty row addresses. Line 8© sets the mixed Hi-Res graphics mode with