Subject: Re: [stella] I'm back! :) ... From: Manuel Polik <cybergoth@xxxxxxxx> Date: Mon, 07 Oct 2002 22:10:14 +0200 |
Hi Ben! >OK, actually I sat down and thought it out, and I >suppose it wouldn't be as hard as I originally >thought...basically just treat the whole 40 column >playfield as a giant register and just do ROLs and >RORs to get the masking bit where I want it. The fact >that the PF0 bits are packed into one byte will be a >minor inconvenience, but shouldn't be anything too >bad... > >I suppose I will try to implement this strategy first >for the playfield drawing routine, since that's a big >ROM hog right now... I used a simple ANDing table to do it: disintigratetab .byte %01111111 .byte %10111111 .byte %11011111 .byte %11101111 .byte %11110111 .byte %11111011 .byte %11111101 .byte %11111110 If you are on a reflected byte, you can EOR #$07 the index, so the same table always does the job. Of course, RORing and ROLing the complete thing back and forth, plus a CLC inbetween can result in a very clever solution, too. Cycle consuming, but ROM saving. Greetings, Manuel ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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