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Atari coding BBS
| Re: Shadebobs wth STE blitter? |
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Posted by: WizTom
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Apr,17.2016-00:07
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There is fast way to do shadebob with blitter but it doesn't go thru all 16 colors, only 15. Lance/Aggression came up with it around time right after braindamage, and we suspect some amiga ppl had discovered it a bit earlier as they did some bit more advance shadebob-style additive polygons, but cant remember that demo's name :(
.. took some time to find the old sourcecode..
basicly you eor plane 3 to 4, 2 to 3, 1 to 2 and just eored plane 4 back to 1.
copypaste-comment from old st source..
"
;kiia v2. eor 3->4 2->3 1->2 new4->1
;kiia v3, inv 4->1 1->2 2->3 3->4 subtracting
;1234 plane
;0000
;
;1000 1
;1100 3
;1010 5
;0111 e
;0100 2
;0110 6
;1101 b
;0011 c
;0010 4
;1011 d
;1110 7
;0001 8
;1001 9
;0101 a
;1111 f
;1000
"
where you have to prefill screen with plane 1 full (to make color 1). then that 4x eor thru planes will make color 1 to color 3, next eor will make color 3 to color 5 etc. all the way down to color f and then back to color 1.
nice this is one can make mask by clearing all 4 planes to 0 that will not have color cycle with eor.
i had some 20'ish 32*32 shadebobs running with simple blittercode on normal ste back then, but they fill the screne too fast and whole thing looks mess. there is aldy way to go colors in reverse (sub colorvalue instead of add) by eor sequence in another order. also, tnx to fixed blit size&count, it shouldn't be too hard to make in into fullscreen, and perhaps have half the bob adding, half subtracing on same rcurve but bit behind to have "shadeworms"..
can try to play around with steem a bit and try to compile working example..
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