[Xorg] Re: X on OpenGL

Jon Smirl jonsmirl at yahoo.com
Sun Jul 11 13:31:13 PDT 2004

--- Alan Cox <alan at lxorguk.ukuu.org.uk> wrote:
> Can opengl effectively extract 2D scroll/blit - that will matter for
> s/w mesa on 2D hardware ?

In Keith's composited model all apps are drawn to textures using
render_to_texture or something similar (pbuffers). In this model
glCopyTexSubImage2D is the same as the bitblt function.

There is also glCopyPixels which allows a rectangle of the display
buffer to be copied from one place to another in the display buffer.

These straight copies aren't as important in the composited model since
many things are alpha blended. You can't scroll something that is
translucent because of the bleed through. 

I don't know if Keith's damage extensions are smart enough to scroll
opaque windows on a compositied desktop. The OpenGL functions for
scrolling are there, but X has to be smart enough to use them.

You can always continue to use XAA drivers on 2D hardware with the
current windowing system. It may be the case that there is no solution
for building a reasonably fast compositied system on existing 2D
hardware. This won't be OpenGL's fault, compositing relies heavily on
alphablended copies and the hardware may not support that.

Jon Smirl
jonsmirl at yahoo.com

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