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BBC Video ULA palette tricks
http://www.retrosoftware.co.uk/forum/viewtopic.php?f=73&t=891
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Author:  DavidB [ Sat Feb 08, 2014 6:48 pm ]
Post subject:  BBC Video ULA palette tricks

I'm fixing up the palette code in Castle Raider so that it will work on the Beeb, so I was reading the Advanced User Guide. The section about the Video ULA is interesting, mentioning "'nasty' effects", which led me to try and experiment a bit in B-Em with the palette registers. It's quite something that you can get multicolour effects in two colour modes, for example, and I wondered if there are games that use the palette registers to increase the number of colours in two and four colour modes without resorting to interrupts. Does anyone know of any?

Author:  TomW [ Sat Feb 08, 2014 7:40 pm ]
Post subject:  Re: BBC Video ULA palette tricks

The Yorkshire Boys 'Retribution' demo uses this at one point for a slightly ropey fade. No games that I'm aware of; it's very tricky to make it look good.

Author:  DavidB [ Sun Feb 09, 2014 7:08 pm ]
Post subject:  Re: BBC Video ULA palette tricks

Messing with the background colour isn't so useful, but the palette for the foreground colours could probably be altered for nice twinkly high score table effects.

Update: This is the sort of thing I had in mind:
Code:
        10 MODE 5
        20 VDU 23,1,0;0;0;0;
        30 FOR A%=0 TO 9
        40 COLOUR (A% MOD 3) + 1
        50 PRINT TAB(2, 4+(A%*2));1000-(A%*100)
        60 PRINT TAB(8, 4+(A%*2));"High score"
        70 NEXT
        80 ?&1000=&20:?&1001=&80:?&1002=&A0
        90 !&1004=&50401000
        100 B%=0:C%=0
        110 REPEAT
        120 *FX 19
        130 FOR A%=0 TO 3
        140 V%=(C%?&1000 OR A%?&1004 OR B%)
        150 ?&FE21=V%
        160 B%=(B%+1) MOD 7
        170 NEXT
        180 C%=(C%+1) MOD 3
        190 UNTIL FALSE


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