>>- Occasionally, the game calculations code overruns the vertical-blank
>>interval, causing the screen to jump by a couple lines for one frame..
>
>This used to happen to me too... if you want an estimate of how much cycles
>you've left for game logic during VBLANK, add an useless loop like this:
>
> LDX #timetowaste
>waste:
> DEX
> BPL waste
>
>and adjust #timetowaste to the maximum value that does not cause the screen
>to jump.
Actually, I made my delay loop something like:
lda INTIM
sta Player0Score
waste:
lda INTIM
bne waste
so because I was using TIM64T, player 0's score would show the number of
64-cycle intervals I had left for game logic. BTW, I found that to be a
very useful debugging device in general - once the score-display routine
was done, I could write any value to the score and have it displayed.
Also, I actually need to begin my draw-screen kernel three scanlines before
VBLANK ends (34 scanlines after VSYNC) because of the scores.. I don't have
20 bytes of RAM to calculate the score displays (five lines, four bytes per
line), so during each three-line block during score display, I calculate
the four bytes for the next three-line block. So I need to calculate the
first line of the score display during the last three lines of VBLANK.
Anyways, did you try the game? What do you think of it?
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