GLX in bad state

Multi-pass rendering is a technique whereby a complex scene is rendered in 
several stages.  The result of an early rendering stage is applied 
to the rendering of a later stage.  This is done when the hardware cannot 
render the complete scene in one pass.

One use of this technique is when the scene requires the application of 
multiple textures to a particular object and the hardware cannot 
accomplish this.  This situation is being phased out as newer cards can 
now apply 8 and more textures per rendering pass.

Another use is in the rendering of shadows.  An object's silhouette is 
rendered from the viewpoint of a light source, and in another rendering 
pass applied to a shadowed object.  AFAIK no hardware can do this in a 
single rendering pass.  Also, realistic shadows are becoming more prevalent
in newer games.

In MS-Win multi-pass renderings are done by rendering directly onto a 
texture and then using this texture.  The OpenGL extension which allows 
this to be done is called WGL_ARB_render_texture.  There is no equivalent 
extension in GLX.

WineX does not render directly onto the texture.  A suitable off-screen 
rendering target (called a pixel buffer) is chosen and rendered into.  The 
result is then transferred into the texture.  By my calculation this 
transfer of pixels into the relevant textures can reach several hundreds 
of MBytes per second.  It consumes valuable video memory bandwidth and 
impairs (sometimes cripples) performance.  

I think the WineX community should support getting valuable WGL extensions
translated into GLX.  Otherwise, Linux gaming will always be at a considerable
disadvantage in comparison to MS-Win.

Thats my opinion.

Nadav Frum
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