Subject: Re: [stella] Unending VDEL hell From: Thomas Jentzsch <tjentzsch@xxxxxx> Date: Mon, 29 Apr 2002 20:41:14 +0200 |
At 29.04.2002, 09:49, Glenn Saunders wrote: > Well, I give up. > I tried to take Thomas' suggestions from a while back and implement them as > literally as I could, and no matter what I do I either get 1-scanline > precision with the 2nd car down a line or both cars offset by 2 scanlines > or on the same scanline but animating in 2-scanline jumps. There are multiple errors in that VDEL code, so by try and error it is nearly impossible to solve them. Here is your code: LDA P0_YFullres ;of player position EOR #1 ; IF ODD,THEN VDEL BNE .SetVDELP0 LDA 1 JMP .ClearVDELP0 .SetVDELP0 LDA 0 .ClearVDELP0 STA VDELP0 LDA P1_YFullres ;of player position EOR #1 BNE .SetVDELP1 LDA 0 JMP .ClearVDELP1 .SetVDELP1 LDA 1 .ClearVDELP1 STA VDELP1 Here are the bugs: 1. you must add AND #1 before or after both EORs, or the branches won't work 2. instead of LDA 0 or LDA 1, you must write LDA #0 or LDA #1, else you will read the first two collision registers. I can't count, how often I made the very same error too :-) 3. the values for P0 are swapped That how it should look like: LDA P0_YFullres ;of player position EOR #1 AND #1 ; IF ODD,THEN VDEL BNE .SetVDELP0 LDA #0 JMP .ClearVDELP0 .SetVDELP0 LDA #1 .ClearVDELP0 STA VDELP0 LDA P1_YFullres ;of player position EOR #1 AND #1 BNE .SetVDELP1 LDA #0 JMP .ClearVDELP1 .SetVDELP1 LDA #1 .ClearVDELP1 STA VDELP1 Then I have cleared the code a "bit", especially by removing the branches. They are unnecessary, the EOR #1 does the job alone. And when you don't need the branches anymore, you can remove the now missing ANDs too. Here is the stunning simple result: LDA P0_YFullres ;of player position EOR #1 STA VDELP0 ;don't care for the bits 1..7, VDEL ignores them LDA P1_YFullres ;of player position EOR #1 STA VDELP1 I hope that helps. Have fun! Thomas _______________________________________________________ Thomas Jentzsch | *** Every bit is sacred ! *** tjentzsch at web dot de | ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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