The place values in a binary number are powers of two. Figure 6-2shows how you use a decimal sum—74—to fire a particular pattern. If you try adding several numbers together, you’ll see that with this system you get no duplicates. The number 6 represents elements 2 and 4 (since 2 + 4 = 6) and there is no other way to get 6 by adding powers of two. This means that any combination of the eight elements adds up to a unique decimal number that falls within the range 0 to 255.

With this labelling system, you fire the top element by sending LPRINT CHR$(128). To fire the bottom graphics element, you send LPRINT CHR$(1). If you want to fire only the top and bottom ele- ments, you simply add 128 and 1, then send LPRINT CHR$(129). By adding the appropriate label numbers together, you can fire any combination of elements you want.

Note: If your computer system cannot send ASCII codes above 127, you will not be able to fire the top element.

A Graphics Program

Now that we have discussed how Dot Graphics works, the following program gives you an example of what you can do. This program creates a series of space invaders. Type the program in exactly as you see it.

10 WIDTH LPRINT 255

20 INPUT "GRAPHICS CODE (K, L)";CODE$

30 INPUT "n1 and n2 PLEASE";N1,N2

40 INPUT "HOW

MANY GRAPHICS DATA";DCOUNT

50 DIM

D(DCOUNT)

60 FOR

J=1 TO DCOUNT

70

INPUT

"DATA";D(J)

80 NEXT J

 

 

90 LPRINT CHR$(27);CODE$;CHR$(N1);CHR$(N2);

100

FOR

L=1

TO

(N1+N2*256)/DCOUNT

110

FOR

K=1

TO

DCOUNT

120

LPRINT CHR$(D(K));

1 3 0

N E X T

K

 

 

140 NEXT L

150END

When you RUN the program, it will first ask you to enter the control code that you want to use for dot graphics. Your choices are <ESC> K or <ESC> L. Enter K to run the program in Single-Density.

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