I had a bit of fun with the horizontal positioning. I'm sure everyone
stumbles on this one.... thank goodness for the list :) The following
routine works for me - it correctly positions (relative to my background)
two sprites described by pixel position "PlayerX". Bin attached shows it in
action. Can anyone improve the initial "divide by 15" for me? I was
thinking something like a divide by 16, and then an adjust... there's a
definite pattern. How are others doing this calculation efficiently (that
is, converting pixel pos to loop counters).
Anyway, here's my current horizontal position routine (which works)...
----------------------------------------------
PositionSprites
; Set the horizontal position of the two sprites, based upon their
coordinates
ldx #1
PosSP
ldy #2 ; fudged start offset
; Count 15-pixel loops
sec
lda PlayerX,x ; absolute X pixel
CountX sbc #15
iny
bcs CountX
; Use remainder for fine adjustment
eor #15
sbc #7 ; -8 to +7
asl
asl
asl
asl
sta HMCLR ; clear any previous movement
sta HMP0,x ; fine movement
sta WSYNC
Jiggle dey
bpl Jiggle
nop
sta RESP0,x
sta WSYNC
sta HMOVE
dex
bpl PosSP
; Now fine-adjust to make it sit nicely on my cubes...
jsr Ret
jsr Ret ; at least... 24 cycle mystery time
lda #%01000000
sta HMP0
sta HMP1
sta WSYNC
sta HMOVE
Ret rts
----------------------------------------------
This uses, essentially, 3 scan lines.... is there a better way?
Thanks
A
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