At 21:02 19.07.99 -0700, you wrote:
>i read in the stella document that there are vertical delay
>registers for that kind of thing (single-scanline
>positioning for double scanline kernals) but im not
>exactly sure how it works :/
The TIA actually has two graphics registers for each of the players
and for the ball. With the VDEL registers you can select if you want
the first or the second graphics register to be displayed. The tricky
part is when the second registers get written to. If you store a value
into GRP0, that value will be put into GRP0-1. At the same time the
value from GRP1-1 will be copied to GRP1-2. When you store a value into
GRP1, that value will be put into GRP1-1 and the value from GRP0-1 will
be copied to GRP0-2. Also the value from ENABL-1 will be copied to ENABL-2.
Writing to ENABL will only change the value in ENABL-1 and has no
influence on the GRP registers. There are no VDEL registers for the
missiles.
What you can do with this is that you could turn on VDEL for one of the
players. Then you can write the graphics for this player in one scanline
and the graphics for the other one at the beginning of the second scanline.
The second write will change the displayed graphics for both players and
therefore make them appear in the same (double)scanline even though you
change the data at different scanlines.
Ciao, Eckhard Stolberg
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