Re: [hatari-devel] Pixel aspekt ratio

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 12/11/2015 09:58, Troed Sångberg a écrit :
> Recently I realized that graphics I made on my Mac and displayed in
> Hatari did not look the same as when I viewed it on my ST. On the ST
> everything was stretched out vertically.
>
> I couldn't really understand why, so I started looking for discussions
> on Atari ST pixel sizes, and found the following:
>
> "and later on the 16-bit Atari ST (low-resolution 320×200 pixels) each
> pixel was roughly .9×1"
>
> https://mmolyneaux.wordpress.com/category/atari-st/
>
> Going by the above I stretched the graphics by a factor 1.11
> horizontally and all of a sudden a photo taken from the graphics as
> displayed on the ST matched perfectly what was displayed in Hatari.
>
> Is this a general thing with modern monitors having square pixels so
> that an emulator with 1:1 mapping will always display things "compress"
> vertically compared to what was originally designed for target?
>
> If so, should Hatari offer the option to not do 1:1 mapping but stretch
> vertically to try to display content as close to what it would look like
> natively?
>
> Sorry if this is a topic that has been debated to death before, it was
> new to me when I stumbled upon it.

Hi

that's something I already read about, but I don't think it was debated 
here.

Problem is : how do you stretch horizontally for example (or vertically 
in the other direction, that's the same) to not get visible artefacts ?

If we consider a 320x200 ST image should be displayed on a 352x200 area 
on modern display, this means that at one point 32 pixels will need to 
be duplicated. Which ones do we chose ? Going from 320 to 352 will sure 
look ugly.

So, to get proper 1.11 ratio we need a much bigger zoom before, maybe x4 
or more. A 320x200 ST image would become a 1420x800 area ; with such an 
increase you can apply some more effective filters for non integer zooming.

In the end, I think it comes down to another request already made here : 
being able to zoom the ST image to any non-integer value. Today, we only 
have x2 zooming, with SDL2 and some additional code, we could have for 
example x3.3 zooming using HW accelerated opengl and some filters.


Nicolas