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Reposition Player 0 routines done



The Reposition Player 0 routines have been rewritten. It now takes 5 scanlines to reposition player 0, plus an additional scan line to get back into sync with the main kernel loop. The player 0 graphics can start on the additional scan line, but a reposition of player 1 cannot be triggered on it as the BMI KernelEvent is what was dropped to get back in sync.


I was surprised that the reposition player 0 routines now take longer than player 1 (it used to take 2 and 3 scanlines respectively). The reason is that while the routines to reposition player 1 had to update just GRP0(graphics for player 0), the routines to reposition player 0 has to update both GRP0 and GRP1. This is because VDELP1 is used, which lets us update GRP1 any point during the scanline w/out shearing being an issue. When using VDELP1, GPR1's update is delayed until GRP0 is written to.


I was able to squeeze in an additional update for NUSIZ0. In the original routines only Player 1 could be resized (it's used for the special room objects). Not sure if we'll have a need for it, but it was a freebie so I went ahead and put it in. A potential use would be for jumbo robots.










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Nice kernel - that must come very close to the limits of the 2600. I hope you will do a robotron game next :)



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Thanks! It's a pretty tight kernel. One thing I took advantage of was the room doesn't span the full width of the screen, so there was a little additional "play" in when TIA updates could occur. The unused space is the first 2 PF pixels and the last 1 or 2 PF pixels depending on the game variation (Frenzy or Berzerk)


Robotron. Hmm - should be doable, but I think the flicker would be horrific.

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