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

58 APPLE II COMPUTER GRAPHICSmuch like it did when you created the data fi le using the previous method .When the program is finished, the speaker will beep and the computer willpri nt the total number of bytes that it saved -write this number downsomeplace. APPLE.EXC is a text fi le which contains a number of DATAstatements, complete with line numbers. Those DATA statements may beeasily appended to your programs. To demonstrate, type:NEWlYJ GR2Y, COUNT = xxx3Y' FOR I = 1 TO COUNT4Y, READ L,V: POKE L ,V5YJ NEXT IlYJYJ ENDEXEC APPLE .EXCThe value assigned to COUNT in line 2(/) should be the number you wrotedown after running Listing 7-5, for that is the number of data bytes in theapple figure.When the disk stops spinning, type:LISTand you will see the program lines you entered above plus several DATAstatements beginning at line 1(/Jf/Jf/Jf/J.When you are ready, type:RUNand the computer will draw the apple on the Low-Res screen.Since the DATA lines are now part of the code, the program does notneed to access the disk for the locations and values. This eliminates thedifficulties inherent in using disk data fi les.We have already stored the data for a figure in two places-the disk andthe program code. There is yet another place to store that info rmation, andthat is within the computer itself.Moving MemoryWhat we will do is store the entire apple screen in memory somewhereother than the Low-Res screen memory area. Then when you wish todisplay the figure, you need only copy the information from the storagearea to Low-Res memory. We will perform the copying fu nction using aBASIC routine, and then also do it using a machine language subroutine.The fi rst task is to load the apple figure into a safe, unused memoryrange. We will use the top $4(/)(/) bytes of user memory, from $92(/)(/) to$95FF (37376-38399). The addresses given here are fo r a 48K Apple II +,