[Mesa-dev] [PATCH] r600g: implement two-sided lighting

[Vadim Girlin]

On Thu, 2012-01-05 at 15:29 -0500, Alex Deucher wrote:
> On Thu, Jan 5, 2012 at 3:06 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> > Am 05.01.2012 17:27, schrieb Alex Deucher:
> >> On Thu, Jan 5, 2012 at 11:10 AM, Andre Maasikas <amaasikas at gmail.com> wrote:
> >>> On Thu, Jan 5, 2012 at 4:58 PM, Marek Olšák <maraeo at gmail.com> wrote:
> >>>> On Thu, Jan 5, 2012 at 9:13 AM, Vadim Girlin <vadimgirlin at gmail.com> wrote:
> >>>>> Rendering in two-sided mode is performed in separate passes for front and
> >>>>> back faces, corresponding colors are selected by semantic ids.
> >>>>
> >>>> Are you sure that r600 cannot do two-sided color selection in
> >>>> hardware? I find it really surprising.
> >>>>
> >>> Not fully automatically afaik, but i guess one can load facing bit
> >>> (FRONT_FACE_ENA?)
> >>> into PS and from there on decide which color to use. This would however require
> >>> shader rewrite/modification
> >>>
> >>
> >> I'll ask the hw guys.
> >
> > I think it would make some sense if the hw didn't support this directly.
> > After all newer APIs always work like that (face register and
> > appropriate pixel shader).
> > If the hw can't do it I think shader modification is definitely the way
> > to go (and the svga driver does this). Maybe the state tracker could do
> > it (optionally of course) if several different hw is affected (or some
> > utility function somewhere). Though it might be some work to get it
> > right (I think for instance you can't have more than 2 color input regs
> > in the pixel shader, hence if you have both specular and diffuse
> > front/back colors some values need to be texcoords).
> 
> I just confirmed internally that the face selection has to be done in
> the shader.  So you'd set SPI_PS_IN_CONTROL_1.FRONT_FACE_ENA, etc. to
> get the face info into a gpr in the pixel shader.  If you calculate
> the lighting in the vertex shader, you'd need to export both results
> to the pixel shader and then use the face info to select the
> appropriate one.  r6xx+ hardware doesn't have specific color/texcoord
> slots, it just has 32 generic param slots that can be used to pass
> data from the vertex shader to the pixel shader.  The hw will do
> semantic matching of params however (e.g., the vertex exports will be
> loaded into pixel GPRs based on the semantic ids assigned to them.
> 

OK, I'll implement it in the shaders.

Vadim

> Alex
> 
> >
> > Roland
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