[Mesa3d-dev] Re: GLX and Xgl

[Ian Romanick]

Owen Taylor wrote:
> On Tue, 2005-04-12 at 10:18 -0700, Ian Romanick wrote:
> 
>>You can be 90+% sure that nobody will hardware accelerate rendering to 
>>pixmaps.  Of course, that doesn't seem to be a problem for you anyway. ;)
> 
> I get the impression that you are looking at the wrong side of rendering
> to pixmaps ... the ability to render to a pixmap via the GL API is 
> really pretty uninteresting. The *implementation* of such is what
> we need.
> 
> Hardware acceleration to "pixmaps" is exactly what we need
> here, because a redirected window is (from the point of view of the
> server internals) a pixmap, and in fact can be named as a pixmap via
> the Composite API.

...which will quite likely never happen.  There *are* reasons that 
OpenGL implementors abandoned pixmaps and invented pbuffers.

> For indirect rendering, we can simply redefine a "pixmap" to be a fbo,
> but for direct rendering, we need something that: 
> 
>  A) Has a global XID
>  A) Can be rendered to by multiple clients
>  B) Is offscreen
> 
> Which is pretty much the general problem of accelerated rendering to 
> a pixmap. We don't have to support rendering to *all* pixmaps, but we
> don't escape what seems to me to be the hard parts of rendering to
> pixmaps.

At this point, I'm pretty confused.  There is no hardware accelerated 
direct-rendering to pixmaps today.  Why will it be missed if it's not 
implemented?  I think I missed some detail as to why this needs to be 
exposed.