Video overlays do only scale when read by the ram dac.
You cant read it back for the normal application cases.
(ingoring framegrabbers and boundary checks for now)
typical overlays have a degree of transparency on a
per pixel base. Thats in no way the sort of AA that
you do want to combine with a normall and "unscaled"
desktop layer. as soon as you do use two layers,
you will get into heavyt troubles when readinb back
and further more into extra efforts for clearing.
automatic scaling is nice for video images when you
dont want or cant switch your monitor/LCD resolution
and must fill in the pixels in between with some
mean value algorithm but dont want to spent up your
grafics memory or your cpu resources for it. further
it provides on the fly color format and depth conversion.
scale blits are rather fast on current grafics hardware
and you should not need to use much "magic" to solve
todays desktop drawings when using such a device.
-Alex.
> -----Original Message-----
> From: Mark Vojkovich [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, November 12, 2002 21:20
> To: [EMAIL PROTECTED]
> Subject: Re: [Xpert]Antialias with video overlay ?
>
>
> On Tue, 12 Nov 2002, David Balazic wrote:
>
> > Hi!
> >
> > I've been toying with this idea to use the video overlay feature
> > as an efficient anti alias method. Is this doable ?
> >
> > Here is how it would work :
> >
> > set the display to some resolution ( higher is better )
> > render your picture ( at a lower , same or higher
> resolution than the
> > display )
> > use the overlay to scale the picture to the physical screen
> >
> > cards with good scaling ( filtering etc. ) would make a nice
> > smoothed picture , right ?
>
>
> Blurrying pictures is not antialiasing them. Antialiasing
> is subpixel rendering implemented by calculating partial-pixel
> coverage and mixing the partial-pixel coverages to get an
> unaliased pixel. Video overlays don't do this.
>
>
> Mark.
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