Indirect rendering with OpenGL-ES in X?

David Jander david at
Tue Oct 6 23:45:28 PDT 2009

Dear Adam,

First of all, thanks a lot for your reply, it is more or less the kind 
of answer I had hoped for.

Adam Jackson wrote:
>> I have:
>> An embedded (linux-) system with a display interface (linux 
>> framebuffer), running kdrive Xserver (Xfbdev) and a MBX 3-D core with 
>> binary OpenGL-ES 1.1 and EGL libraries.
> First, obviously, you are in a world of hurt for running a driver you
> can't modify.  I gently suggest that such hardware _not_ be improved in
> the open code as punishment, so that market forces drive people to
> hardware with a sensible driver story.

I would love to do that, but here in the embedded world, I fear we have 
little other choice. And believe me, I have caused quite some noise 
about this with the chip's manufacturer....

> I think you want:
>> 3. Since the applications will run locally anyway, implement some hack 
>> in the X-server, like shadow-buffers, to update screen contents 
>> efficiently from EGL-pbuffer surfaces.
> You'd want to backend the X server's GLX provider onto your GLES stack,
> which is more or less straightforward, and then just run all GLX apps
> indirect.  GLX pixmap support would be fairly easy, just don't advertise
> any GLX visuals and only-pixmap-enabled fbconfigs, and either point the
> pixmap's storage to the GLES stack's storage (if it lets you get a
> pointer to it) or copy the bits back and forth (if it doesn't).  GLX
> window support would be similarly easy, just allocate the back buffer as
> an EGL pbuffer and copy out of it on SwapBuffers, and hope no one's
> stupid enough to try GL_FRONT rendering.

Sounds interesting. If I understand correctly, I would be using the GLX 
protocol unmodified for GLES (is that possible?), and just write a layer 
to hook the backend up to the GLES libraries. Not advertising any GLX 
visuals would be a way of saying: "I don't support rendering to the 
screen directly". The only caveat will be that probably no _real_ GLX 
application will work since the backend is GLES and not plain OpenGL. 
Since we will be developing our own apps, this shouldn't be a problem.


Best regards,

David Jander

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