[vcf-midatlantic] What's wrong with my program experiment?
evan at snarc.net
Wed Apr 5 14:21:35 EDT 2017
A month-ish ago I posted about my Applesoft learning experiment in which
I figured out how to make a point (in lo-res and hi-res alike) move
around the screen with the joystick.
At the time I couldn't figure out how to keep other images stationary
(vs. redrawing themselves every time the joystick-checking code looped).
Last night I solved that by (duh!) drawing a stationary point first and
then looping back only as far as the joystick code. At first it left a
trail, but then I added a line to immediately re-draw the same
coordinates in black.
20 PLOT 10,10
70 IF X>39 THEN X=39:IF Y>39 THEN Y=39 (because at one point I got an
illegal quantity error when I moved the stick to the right)
80 PLOT X,Y:PRINT INT(X),INT(Y)
90 FOR W=1 TO 50: NEXT W
100 COLOR=0:PLOT X,Y:COLOR=2
110 GOTO 30
This works: the point at 10,10 remains solid while only the
stick-controlled point moves. (I don't want to hear any snobby insults
about "spaghetti code". This is not the actual application I'm working
on. It's just a code snippet for the learning experiment.)
(The results are the same if I eliminate lines 50 and 60. Those lines
only exist to round up the numbers on .5, because INT only rounds down,
and to eliminate remainders when it prints the coordinates.)
However there may be a problem with the joystick or maybe a bug that I'm
All four corners are reporting the correct values: 0,0; 0,39; 39,0; and
39,39. When the stick centers I get 21,12. :( But if I adjust the trim
wheels then the corners aren't right.
Is this a joystick problem or a software bug?
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