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

CHAPTER 7-PRESERVING YOUR PICTURES 57slot. To remedy those problems we present a slightly more complex technique.Using EXECWhat you will do here is create a text fi le of DATA statements on diskwhich may be EXECed into any program that you like. Each record in thetext fi le will contain a line number followed by the DATA statement which,in turn, is followed by ten pairs of entries which are the locations andvalues of the bytes used in screen memory. The last DATA statement maycontain less than the 2© entries the others have. The line numbers for theDATA statements will begin at 1©©©© and increment by two; the set ofvalues in the DATA statements will be the same as those printed with Low­Res Scan #1 .Load the program from Listing 7-1 once again, then enter the fo llowingstatements to mod ify it.10 REM CREATE EXEC FILE35 D$ = CHR$ (13) + CHR$ (4)40 INPUT "FILENAME :";FL$45 PRINT D$ "OPEN" FL$50 PRINT D$ "DELETE" FL$55 PRINT D$ "OPEN" FL$60 PRINT D$ "WRITE" FL$70 LN% = 10000 :Cl = 1104 IF PEEK (L) = 0 GOTO 120106 COUNT COUNT + 1108 IF Cl = 1 THEN PRINT LN%; "DATA" ;110 IF Cl > 1 THEN PRINT II ' II ;112 PRINT L ;", "; PEEK (L);:Cl = Cl + 1114 IF Cl > 10 THEN Cl = l :LN% = LN% + 2:PRINT140 PRINT D$ "CLOSE" FL$15YJ PRINT CHR$ (7) ; "COUNT =" ;COUNT ; "EOJ"Listing 7-5. Low-Res Scan #3 [modifications only].Line 4© requires that you enter a name for the fi le being created. Line 7©sets the line numbers to begin at 1©©©© (LN% = 10000), and line 114increments each line number by 2 (LN% = LN% + 2).With this routine in memory, create the text fi le for the apple figure bytyping:GRBLOAD APPLERUNWhen asked for a fi lename, enter APPLE .EXC. The disk will behave very