Re: OpenGL-based framebuffer concepts

From: Alan Cox
Date: Tue May 23 2006 - 10:34:36 EST

On Maw, 2006-05-23 at 10:10 -0400, Kyle Moffett wrote:
> A GPU which does not support OpenGL at all would look virtually

No GPU today "supports" OpenGL

> 2) Client program sends OpenGL commands through kernel framebuffer
> device.
> 3) Kernel either passes the OpenGL commands to the GPU or if they
> were trapped by the software renderer it passes them to that, which
> can emulate them using more primitive operations.

You've no idea how a GPU works have you ?

The process generally goes something like this.

I build an OpenGL rendering context.
The supporting library JITs an engine which implements this rendering
context and pipeline. Only a JIT is really fast enough because there are
so many tests are otherwise involved.

Each poly is fired down the JIT engine which produces a mix of
- AGP command streams
- GPU bytecodes
- Polygon breakdowns which go back into the engine
(eg for clips the chip can't do)
- Texture loads and swaps

The GPU view of the universe is far far from the OpenGL one. With the
possible exception of the big 3D Labs cards anyway.


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