At 12:34 06.06.99 -0700, you wrote:
>I took a screenshot of Video Chess and overlayed a diagram based on my
>understanding of the kernel.
>
>Please take a look at it and let me know if it's accurate.
Not quite. Your picture says P0 P0 P0 P0 P1 P1 P1 P1, while it should
be P0 P0 P1 P1 P0 P0 P1 P1. Otherwise it seems to be correct.
>I wasn't aware of the ball trick. I can understand using it if you don't
>have enough time to rewrite the playfield register for a nonsymmetrical
>playfield. But aren't there alternatives? Wouldn't it work if playfield
>were set to repeat and the entire board were shifted over to the right (or
>left) by one playfield pixel? Would that throw the sprite timings off?
>Maybe Bob wanted to make sure the board was in the exact center.
The chess board isn't in the exact center of the screen. It is off a bit
to the left. The reason for the ball trick is that using more than one
playfield register for the board would require timed writes to those
PF registers twice per scanline, once for the left half of the screen
and once for the right half. Having to do timed changes to the four
graphics and four colour registers for the player graphics wouldn't
allow you to incorporate that into the code. Besides this, there isn't
much processor time left per scanline to do anything besides what is
already done.
Ciao, Eckhard Stolberg
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