Re: [hatari-devel] Overscan Oddity

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 16/04/2013 13:46, Anders Eriksson wrote:
> On Mon, 15 Apr 2013, David Savinkoff wrote:
>
> > > I didn't have time to look at this at the moment, but I keep it marked
> > > for later.
> > >
> > > Nicolas
> >
> > Hi Nicolas,
> >
> > I'm hoping this problem is fixed for the next release. I'm not familiar
> > enough with this part of Hatari to make code changes (I had a look).
> >
> > It appears to me that 400x300 could be a perfect resolution for
> > low-res recording (aside: and 48000 Hz sample rate) as this would
> > capture everything at it's best (with good performance too).
>
> Hi,
>
> The two overscan methods, 230 byte (common ST overscans) and the 224
> byte (STe only, as used in Save the earth) differ a bit in the screen
> layout.
>
> The shifter outputs 416 pixels width, but the actual usable pixels is
> lower.
>
> 230 byte ST overscan:
> --------------------#
> --------------------#
> --------------------#
> --------------------#
> --------------------#
> The rightmost 6-8 pixels (#)  are a mess due to an extra stabilizer
> frequency switch. That reduces the usable width to about 408-410 pixels.
>
>
> 224 byte STe overscan:
> %--------------------
> %--------------------
> %--------------------
> %--------------------
> %--------------------
> No stabilizer needed here, so the graphics is looking correct all the
> way to the right. However, the entire screen is shifted 8 pixels to the
> right, so there is an 8-pixel empty space at the left.
>
>
> A default cropping to the center 400 pixels is probably a good thing for
> general use. Saint does it that way for example. But it's no good if you
> want the full display captured, so I'd say keep the full 416 pixel
> capture as well. Heck 512 pixel capture (and display) would be very cool
> too (great for plasma coding :).

Hello David

as anders said, 224 byte overscan require to shift the screen 8 pixel to 
the right for correct emulation.

In the IRC part of Save The Earth, this is not visible
, but if you combine 224 byte overscan with raster/plasma or spectrum 
512 like picture (as you in recent DHS demos), you will notice that 
color changes and bitmap are not correctly aligned in Hatari 1.6.0

This was fixed in Hatari 1.6.2 and is now correct.

In your screenshot, we can see that the clock was visible in 1.6.0 
400x300, but the IRC logo is truncated. In 1.6.2, the screen in shifted 
to the right, so you gain 8 pixels to have the IRC logo visible, but the 
clock is truncated by 8 pixels.

So, sorry, it won't be "fixed" for Hatari 1.7.0, that's the way it 
should be emulated.

The basic solution to this is : don't use 400 pixels to corrrectly view 
overscan demos, you need 416 to see all the pixels of the left and right 
border.
Another problem in overscan screens is that they're not "centered" even 
on a real ST : you don't get the same number of pixels in the left and 
right border (56 in left, 88 in right (but you need to remove 12 pixels 
due to the hi/lo stabilizer))

So, you would need to specify in Hatari a different number of pixels to 
display in left border and another one in right border (this was 
possible in earlier version 0.9 or 1.0 maybe).
Now the config specify a total width, so you can't really choose how to 
center the screen with regard to the borders' size.

I'm still planning a major rewrite of STF/STE video emulation later, 
with a possibility to specify each left/right/top/bottom border with a 
pixel precision, and then to apply a x2 zoom on X/Y axis (I don't think 
the current width x height configuration is adapted for STF/STE mode 
when you want to control each border, only for VDI mode where borders 
don't matter).

Nicolas