Re: [Xpert]Antialias with video overlay ?

[Scott Long]

On Tue, 12 Nov 2002 15:09:37 +0100
 David Balazic <[EMAIL PROTECTED]> wrote:

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 ?

The only option you mention that could possibly work would be to render the image at a *higher* resolution than the display resolution, then scale the image down using coverage-weighted averaging. This is known as "supersampling" and is how many AA algorithms work.

Your other options would make the image "smoother," but only because they would blur the image. You can't resize an image to a larger size and get more detail out of nothing. The only effect a filter would have would be to smear the image.

Examples of use :

 - text anti-alias :
  render the text at lower resolution, then scale it up
  to some higher resolution, and get AA filtering for "free"

 - 3D FSAA : render at higher resolution, scale down to get FSAA
   ( using the same resolution ( 1:1 scaling ) might give something
    useful too ? )

Opinions ?

Unfortunately, that won't work at all. What you want to do is render the text at a *higher* resolution and then scale the result *down* to the display resolution using coverage-weighted averaging. You can't get anything for free! If you tried what you suggest, what you'd end up with would be a blocky character that shows stairstepping, except the stairsteps would be blurry. Not only ugly, but a headache-inducer :-)

There are many (and *much* better) techniques for antialiasing fonts in particular that don't resort to this brute-force supersampling method.

Scott Long
SwiftView, Inc. http://www.swiftview.com
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