Overscan Demos

All about ST/STE demos

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Steven Seagal
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Overscan Demos

Postby Steven Seagal » Thu Dec 08, 2011 7:43 pm

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.
In the CIA we learned that ST ruled
Steem SSE: http://sourceforge.net/projects/steemsse

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npomarede
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Re: Overscan Demos

Postby npomarede » Thu Dec 08, 2011 8:42 pm

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 :) )

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Steven Seagal
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Re: Overscan Demos

Postby Steven Seagal » Thu Dec 08, 2011 9:30 pm

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.
In the CIA we learned that ST ruled
Steem SSE: http://sourceforge.net/projects/steemsse

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npomarede
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Re: Overscan Demos

Postby npomarede » Thu Dec 08, 2011 9:55 pm

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 :-)

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Steven Seagal
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Re: Overscan Demos

Postby Steven Seagal » Sun Feb 19, 2012 8:47 am

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
In the CIA we learned that ST ruled
Steem SSE: http://sourceforge.net/projects/steemsse

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Re: Overscan Demos

Postby Steven Seagal » Sun Dec 15, 2013 7:12 pm

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.
In the CIA we learned that ST ruled
Steem SSE: http://sourceforge.net/projects/steemsse


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