GLX_EXT_texture_from_pixmap

[Adam Jackson]

On Monday 06 February 2006 07:58, David Reveman wrote:
> Hey,
>
> here's the latest version of the texture from pixmap spec that Xgl will
> be supporting. It's not fully implemented in Xgl yet, just so much of it
> that you can get an indirect rendering compositing manager running using
> it.

Regarding issue 5 (rebinding and texturing directly from the pixmap image), 
I've suspected for a while now that we need some form of protocol whereby 
apps can signal to the compositing manager that they've rendered a frame to a 
given pixmap and therefore that it should be rendered from quickly.  Others 
have proposed using sync counters as an even/odd toggle indicating whether 
the pixmap is "baked" or not.  I think we want the ability to specify live 
updates to the pixmap as an (optional) attribute to BindTexImage to 
accomodate for this sort of handshaking in the future.

Other than that it's been fairly easy to hook this - well, "this" when it was 
still called EXT_texture_from_drawable - up in the GLX implementation in the 
xfree86 DDX, and we've been pretty pleased with the results so far.  I don't 
see anything in this revision that will make life any harder in the xfree86 
DDX.

Currently we're just doing TexImage2D to dump the bits from the pixmap to the 
texture, which is suboptimal but works surprisingly well as long as your 
pixmaps are in host memory (thank you, XaaNoOffscreenPixmaps).  In the future 
there's probably some integration to be done with the GetImage path for 
accelerated downloads, or with on-card copies from pixmap storage to texture 
storage, or live updates as mentioned above.  Also in the medium-to-long term 
we should look into unifying the GLX code between the xgl and xfree86 DDX's.  
I haven't had the chance to look at the xgl side in too much detail, but I 
expect there's some common themes.

- ajax
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