Xgl and direct rendering

[Matthias Hopf]

On Feb 28, 06 19:57:29 +0100, Anders Storsveen wrote:
> what exactly is an overlay, I've heard about Hardware Overlay, Video
> Overay, Opengl Overlay, and more? what is it?

Hardware Overlay is typically only handwaving for video overlay. It
means there is a second scanout engine, that works independently on a
second framebuffer with a different resolution and color space
(typically YUV for XVideo), and a color key in the primary framebuffer
decides whether the primary or this secondary framebuffer should be
visible at any given pixel.

The secondary scanout engine has to perform color conversion and scaling
on-the-fly, and typically has very well designed 7tap filters for
scaling, which are better than bilinear filters (which are the default
for textures).

OpenGL overlay is something similar for OpenGL, and it hurts my brain
when I think of it. It is something used for user interfaces in ancient
OpenGL applications, and should never ever be used in modern
applications. Use imposters for your scene graph here, if rendering the
main model view is too slow for immedeate update.

Matthias

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