Subject: Re: [stella] Cosmic Ark scanline pixel doubling From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx> Date: Sat, 12 Mar 2005 09:05:13 -0500 |
> I assume you're refering to this post from back in 1997? > http://www.biglist.com/lists/stella/archives/199705/msg00061.html Yes, that's what I'm referring too. Although I later found out that the shift actually is 17 pixels to the left in each scanline. Also the "missing" pixel always happens in the scanline that comes after a scanline where the missile was displayed over the first pixel of a playfield block. > I think my version gets the various NUSIZ tricks right. These just sort > of fall out naturally. But I'm at a bit of a loss for the HMOVE tricks. > I've tried walking through this logic a few times before, but I get lost > in the intricacies of exactly what happens when HMOVE gets hit before > the required setup time has occurred. Andrew Towers describes the HMOVE handling and the Cosmic Ark starfield effect quite nicely in the document that you linked to in one of your last messages. He only doesn't mention the pixel doubling for the missiles. The important part in the Cosmic Ark effect is that the HMOVE logic will continue to send a shifting pulse every 4 pixels. During the horizontal blank this will result in a 17 pixel shift to the left. But during the visible part of the screen the clock line for the HMOVE shifting pulses is used for different things, like advancing the pixel counter for the line. So on most VCSs the extra HMOVE pulses have no effect during the visible part of the screen. In the 4 or 5 pixel setup logic for the movable object display there must be something driven by that clock line, that could be confused, if the HMOVE clock happens in such a way that it would cancel out the normal clock pulse. Do you know how the setup logic for the movable object display works? Is there something in there that is driven by the same clock line that is used for HMOVE shifting pulses? Ciao, Eckhard Stolberg Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
Current Thread |
---|
|
<- Previous | Index | Next -> |
---|---|---|
[stella] Cosmic Ark scanline pixel , Adam Wozniak | Thread | Re: [stella] Cosmic Ark scanline pi, Andrew Towers |
Re: [stella] Dumping ROM images, Eckhard Stolberg | Date | Re: [stella] Dumping ROM images, Eckhard Stolberg |
Month |