Palette rotation: Difference between revisions
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(Example code (please test !)) |
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==Example code== | ==Example code== | ||
(You really should just load a pre baked palette entry instead of computing it) | |||
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Revision as of 13:30, 24 September 2016
Palette rotation is a non-NeoGeo-specific video effect made by shifting a range of color entries inside a palette.
This effect was frequently used along auto animation for cyclic, scrolling animations (waterfalls...) without having to use multiple tiles, saving up graphics memory and VDC time.
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League Bowling's title screen uses palette rotation as a mean to provoke eye cancer.
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Fatal Fury 2 uses palette rotations to animate water efficiently.
Example code
(You really should just load a pre baked palette entry instead of computing it)
; Untested ! Doesn't care about transparent index.
; Executes in about 720 cycles
lea COLOR_LIST,a0 ; Pointer to list of 32 colors
lea 64(a0),a2 ; End of list (32 words)
lea PALETTE,a1 ; Pointer to start of palette in palette RAM
clr.l d0
move.b ROT_INDEX,d0 ; Offset variable
move.b #16,d7 ; Number of entries in palette
andi.b #31,d0 ; Warp on 32
add.w d0,d0 ; Colors are words
movea.l 0(a0,d0),a0
-:
move.w (a0)+,(a1)+ ; Copy
subq.b #1,d7
beq + ; Are we done ?
cmp.l a0,a2
bne - ; Warp ?
lea COLOR_LIST,a0 ; Warp !
bra -
+:
addq.b #1,ROT_INDEX ; Animate