Re: [hatari-devel] Display problem in Paradox latest demo

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 28/12/2013 17:53, Anders Eriksson a écrit :
> Hi,
>
> just wanted to inform that Hatari doesn't display Paradox newest STe
> demo properly (released today).
>
> As far as I can tell, the entire demo runs at 60 Hz, which is a bit
> unusual in itself, but the final screen also appear to remove the lower
> border at 60 Hz. I think Neochrome Master might be the only other
> program to do that?

I think it's to reduce color flickering with the 2 different dithering 
pictures ? A higher framerate can slightly limit it (I remember the old 
TEX's spectrum 512 slideshow was running in 60 Hz too).

> The result is that Hatari freaks out pretty bad, it jumps from
> low/medres randomly (set Hatari without zoom then you'll see the window
> change size constantly) and there is garbage graphics displayed as well..

Hatari handles bottom border's removal in 60 Hz since quite some time ; 
I didn't check neochrome master, but leaving terramis is using it (the 
kind of spectrum 512 picture displayed while loading next level).

A 60 Hz screen has only 263 hbl, but I see the demo is switching to med 
res on hbl 259, so the last 4 lines of the screen are displayed in med 
res, I don't see the point. Maybe something is displayed on a real STE 
that we don't see on Hatari ? But it's just seem to show some garbage lines.

Anyway, the problem is that the timing they chose for bottom border 
removing is really tight. The 50/60 Hz switch sometimes goes back to 60 
Hz at cycle 500, while Hatari considers the min value should be 504, 
else no removal should occur.

This is what I once measured on real STE, but I only checked in 50 Hz, 
and as 60 Hz lines start 4 cycles earlier, this could explain the 
differences ; I would need to write a more complete version of my test 
program later to check all those timings again.

For now, I added a 4 cycles tolerance to this case, so the demo should 
now run OK :)

Thanks for reporting it

Nicolas