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Forums > C64 Coding > setting nibbles for chunky FLI

2016-10-07 17:53

Digger

Registered: Mar 2005
Posts: 422

setting nibbles for chunky FLI

A classic one but couldn't find any relevant threads in this forum
what's the fastest way for merging color nibbles for the screen RAM (chunky FLI, plasmas, whatever) that you've came across?

The non-optimised being:

lda #colorL
ldx #colorH
ora nibbleLUT,x
sta $0400

* = $80

nibbleLUT: .byte $00, $10, $20, $30
           .byte $40, $50, $60, $70
           .byte $80, $90, $a0, $b0
           .byte $c0, $d0, $e0, $f0

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2016-10-09 06:33

ChristopherJam

Registered: Aug 2004
Posts: 1382

Oswald, it accesses your sparse table, just relocated to $8L8H

The y register is zero, and a row of pixels are stored in a buffer in zero page. Each pair of pixels is treated as a pointer.

2016-10-09 07:40

Oswald

Registered: Apr 2002
Posts: 5031

ah I get it.

actually its on par with the ABS method hence the writes to zp are faster by 1-1 cycle.

in some cases it might be the better choice over the abs one. usually sta's are fixed in 4x4 per pixel style effects, imho the benefit would come from that the writes happen to the same zp buffer and they get translated to fullscreen.

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