Re: [stella] Invaders update! - inv-beta.bin

Subject: Re: [stella] Invaders update! - inv-beta.bin
From: emooney.KILL.SPAM.@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Thu, 24 Apr 1997 17:19:29 GMT
>>- 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
> 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:
sta Player0Score
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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