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Overscan Demos

Posted: Thu Dec 08, 2011 7:43 pm
by Steven Seagal
I believe the nice Overscan Demos were made by members of this forum.
I notice that Hatari renders decrunching in blue, and Steem in all colours.
What's it supposed to be?

Image

Image

And SainT also in all colours.

Re: Overscan Demos

Posted: Thu Dec 08, 2011 8:42 pm
by npomarede
2 reasons to this :
- Hatari is in STF mode, while Steem is in STE mode ; set Hatari to STE mode, and you will get the same result
- I don't know how Saint works, but I guess it sets unused bits to 1 (or to random) in the color register, while Hatari sets them to 0

(the real values of the unused bits was discussed in another thread, and is supposed to be related to the data that were most recently accessed on the bus ; Ijor certainly knows this better than I do :) )

Re: Overscan Demos

Posted: Thu Dec 08, 2011 9:30 pm
by Steven Seagal
Thanks, another mystery solved...
And another "funny" bug in my code, Steem was in STF mode:

Code: Select all

#if defined(STEVEN_SEAGAL) && defined(SS_STF)
    if(!ST_type==STF)	// STF; probably useless
    {
      io_src_w&=0x0777;
    }
#endif
You see, I had thought of setting those bits to 0 too, except for some reason I did it on the STE (!ST_type==STF) instead of the STF... oops! I like the comment too, should have written // STF; probably another bug
Now Steem behaves like Hatari (blue for STF). And SainT displays in all colours in STFM mode.

Re: Overscan Demos

Posted: Thu Dec 08, 2011 9:55 pm
by npomarede
Steven Seagal wrote:

Code: Select all

    if(!ST_type==STF)	// STF; probably useless
Hmmm, wouldnt'it be more readable and less error prone to simply write "if ( ST_type != STF )". you're really looking for complication here :-)

Re: Overscan Demos

Posted: Sun Feb 19, 2012 8:47 am
by Steven Seagal
Well I'm still working hard on Steem, it's full of bugs (my build!). When I squash a bug, I find a hack isn't working anymore, etc. I have much trouble with the border size option.
Here for Overscan #6 for example, I thought larger borders would be great, until I spotted glitches that ruin the experience (at first I thought it was a bad scan):
Image
And another "hack" to remove them, but now I must do more tests again, in case it breaks anything:
Image
I also thought that the moving (after a while) Atari symbol was an emulation issue, but in fact it's a feature, it follows the music!


EDIT:
The picture above is a hack that's no good. For a reliable emulation, it seems we must shift the display 4 pixels to the left, apparently real ST worked so when the left border was removed (it shifts the bitplanes for the shifter...) Consequence: 'very large border' mode not so beautiful because of the shift, like in other emulators, but at least no glitches.
I know 2 cases where it's important: here, and for D4/Tekila. I consider a hack that would do the shift only when really necessary.
Another screenshot, maybe you can see the shift:
Image

Re: Overscan Demos

Posted: Sun Dec 15, 2013 7:12 pm
by Steven Seagal
npomarede wrote:2 reasons to this :
- Hatari is in STF mode, while Steem is in STE mode ; set Hatari to STE mode, and you will get the same result
- I don't know how Saint works, but I guess it sets unused bits to 1 (or to random) in the color register, while Hatari sets them to 0

(the real values of the unused bits was discussed in another thread, and is supposed to be related to the data that were most recently accessed on the bus ; Ijor certainly knows this better than I do :) )
Another case tells us it's "random": UMD 8730 and here it's important, the demo stalls if it's all 0 or all 1.
So the correct decrunching in Overscan Demos should be all colours for STF too.
I think SainT sets those bits, because UMD 8730 stalls there too.