On Thu, 14 Nov 2002, David Balazic wrote:
> Video overlays perform some filtering , right ?
>
> antialias is usualy = supersampling + low-pass filtering.
> supersampling : use higher resolution
> low-pass : use overlay hardware
>
> Am I missing something ?
> I admit I don't know how usually overlay filtering/resizing works.
Here are some facts:
Many video hardware don't support downscaling (too much bandwidth).
Of the ones that do downscale, many don't filter (too much bandwidth).
The filters, at least on newer hardware, are not linear filters.
They are higher order filters, which might cause some ringing artifacts
when trying to do this. I haven't thought about it much.
I don't know of hardware that supports more than 2048 x 2048
overlay sources. That means for a 2x2 AA (which is pretty lame
for text rendering) you'd be stuck with a maximum screen size
of 1024x1024. Many hardware only support 1024x1024 and much
of the older hardware don't have the bandwidth to display that.
This sort of fullscreen AA would require that you expand all 2D
rendering (including core primitives) to larger sizes so they
downsample to the correct size. This would effect all rendering.
How this interacts with things like OpenGL is complicated.
Assuming you could solve the technical issues with OpenGL and 2D
primitive expansion, I expect the quality of a 2x2 supersampling
wouldn't be acceptable for text rendering, and the current video
hardware wouldn't allow this to work for desktop sizes that people
use. Besides, video overlays will likely be disappearing from
hardware sometime in the not-so-distant future since the operating
systems with majority market share are abandoning them.
Mark.
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