[Mesa-dev] Mesa as part of OpenGL-on-OpenGL ES 2.0 (/WebGL)?

[Michel Dänzer]

On Die, 2012-03-06 at 08:19 -0800, Benoit Jacob wrote: 
> ----- Original Message -----
> > On Mon, 5 Mar 2012 19:41:14 -0800 (PST), Benoit Jacob
> > <bjacob at mozilla.com> wrote:
> > 
> > >  - glShadeModel(GL_FLAT) (this one seems really hard to do with
> > >  OpenGL
> > >  ES2, a real capability regression from OpenGL [ES] 1 it seems!)
> > 
> > Ouch.  I keep trying to come up with workarounds for this, but I'm
> > ending up with things that use even later GL functionality.  Rewrite
> > your VBOs, I guess, but that gets really awful in the case of vertex
> > shading.
> 
> About glShadeModel(GL_FLAT), rewriting VBOs if of course what I would
> like to avoid; the biggest hope I've had was from this page,
> suggesting implementing it using OES_standard_derivatives (which is
> already widely available as a WebGL extension): 
> http://athile.net/library/blog/?p=970
> 
> I would like to understand: when Mesa uses Gallium3D, at what level is
> glShadeModel(GL_FLAT) handled? Is the VBO rewritten before it hits
> Gallium3D, or does Gallium3D accept flat shading (which would mean
> that implementing a Gallium3D driver targeting WebGL would require us
> to handle glShadeModel(GL_FLAT) ourselves)?

The latter. However, Gallium3D offers several options for implementing a
workaround, either in the driver only or with the help of auxiliary
functions and/or the OpenGL API state tracker.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer