Subject: Re: [stella] Sprites source code From: emooney1@xxxxxxxx (Erik K Mooney) Date: Sat, 15 Mar 1997 19:11:12 EST |
>It still sort of "trips over" that 15 there, but it's accurate enough >for most purposes. There certainly isn't much danger of erratic jerking >around, it'll just snag on every 15 pixels. In real life, the left >side of the screen is 0 and the right side of the screen is 152 (160-8). >Here, the left side of the screen is 8 (eight), and the right side of >the screen... uh, I'll figure it out later. Why is the right side of the screen 152 and not 160? I was experimenting with sprite moving, and, on PC Atari, whenever RESP0 happened at 144 or later, the sprite would get displayed on the left side of the screen instead of the right (couldn't tell if it was dropping down a scanline or not - I suspect it was) .. if I limited its X-coordinate to 143, it worked fine. The right side of the screen being 152 instead of 160 would explain what I saw, but why can't we use those last eight pixels for sprites? Playfield gets displayed fine in those columns (haven't tried missile/ball.) Also, in PC Atari, both real-time and in the debugger) there seemed to be a two-cycle (six pixel) delay after the STA RESP0 completed until it took effect.. as in, I began the STA RESP0 at cycle 22, it completed at cycle 25, which should be the 75th pixel after WSYNC and 7th from the left edge of the screen... but PC Atari displayed it as "RESP0=12" (six more than where it should be, because PC Atari counts from zero) both onscreen and in the debugger. Is there always a delay after a write to RESxx? And if so, is this delay the reason why you can't use the last few pixels of the screen? One other question - Is HMP0 reset after writing to RESP0? When I wrote HMP0 before RESP0, the sprite jumped at 15-pixel intervals.. if RESP0 was written before HMP0, it moved smoothly. -- Archives available at http://www.biglist.com/lists/stella/archives/ E-mail UNSUBSCRIBE in the body to stella-request@xxxxxxxxxxx to be removed.
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