Re: [stella] VDEL...

Subject: Re: [stella] VDEL...
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Sun, 24 Feb 2002 16:38:41 +0100
> >With VDEL you can update one
> >of the players at anytime you want during the two 
> scanlines.
> Hm... how would that work? Could you post some little 
> example?

I don't have an example myself, but you can look at the
commented Combat code, which uses this method I think.

Remember how VDEL works. There are actually two graphics
registers for each player (GRP0-A, GRP0-B, GRP1-A and GRP1-B)
and VDEL only selects whether to use the A or the B register
for the output. Whenever you write something to the GRP
register of one player this data gets written to the player's
A register. But at the same time the data from the other
player's A register gets copied to the corresponding B register.

So if you update the graphics for both players on alternating
scanlines, and turn on VDEL for only one of them, then both
players will have their display changed in the same scanline.
By chosing which players VDEL is turned on, you can get
single line positioning precission (but only double line
display resolution) even with a two line kernel.

Ciao, Eckhard Stolberg

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