At 08:36 05.06.99 -0700, you wrote:
>>The BALL is eight pixels wide and positioned at pixel 44. It gets
>>enabled for even chessboard rows to display the background for column A.
>
>Why exactly is this necessary? By background you mean the blue background?
> Wouldn't that already be there?
In this case background means the light blue chess board squares in
column A. The chess board is mostly made of PF2 and the playfield
is set to reflect mode. That means, that PF2 will be displayed from
the last bit to the first and then immidiately from the first to the
last. In rows where the chess board starts with a dark square, $66 is
stored in PF2, which would display as _xx__xx_ _xx__xx_ . As you can
see, there are four light blue squares. In rows that start with a
light blue square, $98 is stored in PF2, which would display as
__xx__x x__xx__ . As you can see, there are only three light blue squares.
Therefore the ball is set to eight pixels width and positioned so
that it would show up as a light blue square in column A.
>Hmm. I wonder if it would have been possible to bit-pack the color storage
>since there are only two possibilities. Probably too slow.
Yes that would be too slow to decode during display time. Also you
wouldn't gain much by this, since these eight bytes are used as the
processor stack for calling subroutines during the non display part
of the screen.
>Has anyone tried hacking the color so that there is a better contrast
>between black and white? I don't think it's possible to have the black
>sprite be black, right?
It wouldn't be too easy. As it seems, the addresses, where the colour
values are stored are also used for other purposes, so that you can't
simply change them. And reading the colour values in a different way
would change the code timing and therefore mess up the display. Unless
someone is willing to do some major changes to the Video Chess code
I don't think it's possible to alter the colours.
Ciao, Eckhard Stolberg
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