[stella] VDEL problems again
Subject: [stella] VDEL problems again|
From: Glenn Saunders <cybpunks2@xxxxxxxxxxxxx>
Date: Tue, 19 Mar 2002 00:15:26 -0800
After several months I spent a bit of time going over the DD code again and
I have to admit I'm a little rusty.
I still can't understand how to properly implement VDEL. (Here we go again).
I really am trying, though.
I took a look at the Combat disassembly and I aligned my sprite writes
GRP0 is written right after the WSYNC on the first of the two
line-pairs. GRP1 written close to the end of the 2nd line-pair. I'm
assuming that the GRP1 write timing is not critical, just GRP0.
I'm also assuming that regardless of the desired Y position of GRP0 or GRP1
that I can leave it like this, or am I going to have to have a separate
kernel where GRP1 is written first, and then GRP0? I didn't see that sort
of thing in Combat.
Now, as long as I set both sprites to the same Y position, enable VDEL for
P0 and disable VDEL for P1, the cars line up properly even though I'm
writing on alternate lines.
However, when I use the code below to automate the settings for VDEL, I can
no longer get the cars to align at 1-scanline accuracy:
LDA P0_YFullres ;vertical delay becomes
STA VDELP0 ;least significant bit
LDA P1_YFullres ;of player position
EOR #1 ;(thoughtfully placed in bit 0
STA VDELP1 ;by Stella's designers)
Even if I experiment with hardcoded values I can't seem to figure out how
this should be working.
Anybody know what I'm doing wrong?
I can't wait to get this behind me so I can try to wedge the missiles in
and then start working on animation routines.
Glenn Saunders - Producer - Cyberpunks Entertainment
Personal homepage: http://www.geocities.com/Hollywood/1698
Cyberpunks Entertainment: http://cyberpunks.uni.cc
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