Re: [stella] Qb/Demo background animation (very rudimentary)

Subject: Re: [stella] Qb/Demo background animation (very rudimentary)
From: "Andrew Davie" <adavie@xxxxxxxxxxxxx>
Date: Tue, 6 Feb 2001 01:15:06 +1100
> If this demo works in PCAE, you must be using a pretty old version of
> this emulator. I tried PUSH.BIN on my 7800 and the sprite positioning

I guess it's time to update.  Yes, the demo works on my version of PCAE (and
I just checked the date - 22/August/1997 !!) so I guess that's basically why
it looks good to me.  It is quite interesting that, despite what you say

> Due to the fact that each cycle represents three pixels, you can't
> position an object on any pixel with RESxx alone. Therefore you now

I could, in fact, do this when using PCAE :))

What I was doing a WSYNC, then an immediate RESPx.  Then I did a loop (I
only have to position to exact 20-pixel boundaries) which did multiple
4-pixel shifts.  Each shift I did a store HMPx followed by an immediate
HMOVE.  It worked for me - but obviously wrong!

I appreciate VERY MUCH your detailed explanation of how it is supposed to
work.  I am also pleased to find out that my emulator is so old and
incorrect - I will update to the new version ASAP!

> One other thing that I noticed on your demo is, that it only does about
> 249 scanlines per frame, and every couple of scanlines there is a frame
> where you do a different number of scanlines, so that the screen jumps.
> Z26 displays the number of scanlines in the last completed frame, when
> you start it with the -n command line switch. This could help you to
> generate a proper display.

Thanks for this information - I was aware of the jiggle, but it was one
thing to fix up later.  I didn't know the jiggle was due to my differing
scanlines (accidental), but it is very handy to know that.

> Also you should do a STA WSYNC before you turn on VSYNC. Otherwise you
> might turn on VSYNC at the end of a scanline and therefore do only
> 2 scanlines of VSYNC effectively.

Once again, THANKS!


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