Radio Shack TRS-80 - Chapter 9: Cassette Tape Operations; Recording Programs

Computer Graphics Operation Manual
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Reads and prints the value of the pixel at the point's
coordinates (3~~,1~~) and displays its value: 1.
PRINT &POINT(3~~~,1~~~)
Since the pixel is off the screen, a -1 is returned.
PRINT &POINT(-3~~~,-1~~~)
Since the pixel is off the screen, a -1 is returned.
PSET ( 2~~ , l~~) ,11
PRINT &POINT(2~~,1~~)
Reads and prints the value of the pixel at the point's
coordinates (2~~,1~~) and displays its value: 11.
l~ PSET(3~~,1~~),1
2~ IF &POINT (3~~, l~~ )=1 THEN PRINT "GRAPHICS BASIC!"
Sets the point ON. Since the point's value is 1, line 2~ is
executed and Graphics BASIC is displayed:
GRAPHICS BASIC!
5
SCREEN ~
l~ PSET(RND(64~),RND(24~»,1
2~ IF &POINT(32~,12~)=1 THEN STOP
3~ GOTO l~
Sets points randomly until (32~,12~) is set.
5 CLR
l~ LINE(5~,8~)-(12~,l~~),1,BF
2~ PRINT &POINT(1~~,8~)
3~ PRINT &POINT(11~,8~)
4~ PRINT &POINT(115,9~)
5~ PRINT &POINT(5~,4~)
6~ PRINT &POINT(13~,12~)
The first three pixels are in the filled box, so the value 1
(one) is displayed for each of the statements in lines 2~,
3~,
and 4~. The pixels specified in lines 5~ and 6~ are not
in the shaded box and ~s are returned.
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