Sorry if this is a repost...it didn't seem to go through?
Aargh, this is maddening.
On my way to something like skipdraw, I realized that I was going
through too much logic to figure if I should draw the wingup or the
wingdown graphic, I needed to set a 2 byte pointer to current graphics
frame in the VBLANK.
I just started with P0:
I set up a 2 byte variable:
pointerP0Graphic ds 2
In my initialization I set up the second byte of that
with the page I'm putting all the graphics on:
LDA #>GraphicsPage ;grab the hight byte of the graphic location
STA pointerP0Graphic+1
later, I either do
LDA #<WingUpGraphic+1 ;add in the low byte of the graphic location
STA pointerP0Graphic
or
LDA #<WingDownGraphic+1 ;add in the low byte of the graphic location
STA pointerP0Graphic
Now, I'm pretty sure that that's all correct, because I
can put that graphic inplace of the score, on its just about
what I expect:
LDA (pointerP0Graphic),Y
; LDA (pointerP0Score),Y
STA GRP0
It flaps and looks ok, just a little truncated, which makes
sense.
Now, for now I'm using a byte, p0DrawBuffer to buffer, and then
putting that in GRP0 at the begining of the line. So my logic has
P0VisibleLine counting down from 8 to 0, showing which line is visible.
LDA #00
;if the p0VisibleLine is non zero,
;we're drawing it
LDX p0VisibleLine
BEQ FinishPlayer0 ;we're done drawing
DEC p0VisibleLine
LDA (pointerP0Graphic),X ;what's wrong with this???
;LDA #%10011001
FinishPlayer0
STA p0DrawBuffer
Now, because I can put the pointerP0Graphic into score,
I think I'm setting it right. And that commented out LDA #%10011001
when restored, shows that the Accumlator->P0DrawBuffer ->GRP0
is working fine, because if I uncomment it I see that pattern.
Commented, GRP0 seems to be random garbage that varies even
with P1 flapping, so I don't know where the heck LDA (pointerP0Graphic),X
is getting its data from...
Is there some gotcha to use Indirect Indexing with the X
register I'm missing? It's driving me nuts, because it seems
to be isolated to that line...
Full source and binary at the top of http://alienbill.com/joustpong/
Doggone it. I thought I was doing well to.
--
KirkIsrael@xxxxxxxxxxxxx http://kisrael.com
"The desires of the heart are as crooked as corkscrews." --W.H.Auden
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