[vcf-midatlantic] What's wrong with my program experiment?

Jeffrey Brace ark72axow at gmail.com
Wed Apr 5 23:11:24 EDT 2017

On Wed, Apr 5, 2017 at 2:21 PM, Evan Koblentz via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> 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

That's cool how you discovered a trick used in the early days of
programming these computers!

> However there may be a problem with the joystick or maybe a bug that I'm
> not seeing.

You didn't include the code for the joystick. This may help de-bug it.

> 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?

I'm not sure I understand what the problem is exactly. You were able to
move the image and have it erased. Does it not continue to move and erase?
Is the problem with the coordinates resetting when the stick centers?

I assume that "IF X>39 THEN X=39:IF Y>39 THEN Y=39" means that you want to
keep the image on the screen and not go off the screen. If this is the
case, then you also want to do it for the left side of the screen when it
is 0. "IF X<0 THEN X=0:IF Y<0 THEN Y=0".

Jeff Brace - ark72axow at gmail.com
Sent from my Commodore 64

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