[Mesa-dev] first attempt at shader stencil export
jfonseca at vmware.com
Thu Sep 30 07:53:55 PDT 2010
On Thu, 2010-09-30 at 07:44 -0700, José Fonseca wrote:
> On Thu, 2010-09-30 at 07:32 -0700, Brian Paul wrote:
> > On 09/30/2010 12:41 AM, Dave Airlie wrote:
> > > some background:
> > >
> > > so on r600g, the only way to directly write to the stencil is via the
> > > shader, using a transfer would require an extra step to flush the DS
> > > buffer out via the pipe again to make it useable by the hw as a DS
> > > buffer. So using the current gallium stencil draw would be a major
> > > overhead, compared to just doing it properly.
> > >
> > > So to do it properly I decided to expose the
> > > GL_ARB_shader_stencil_export type functionality.
> > >
> > > http://cgit.freedesktop.org/~airlied/mesa/log/?h=gallium-stencil-export
> > >
> > > 7 commits in here:
> > >
> > > two simple one liners, add the cap to gallium headers, and add
> > > FRAG_RESULT_STENCIL to mesa.
> > > then a "fix" to the mesa texstore so it will store S8 in an 8/24 so we
> > > can put the stencil values in a texture.
> > > mesa state tracker support to use the new capability to hw accel
> > > drawpixels on the stencil (outputs to Y of FRAG_RESULT_STENCIL).
> > > r600g support for the capability take the second
> > > TGSI_SEMANTIC_POSITION output and use its Y value as stencil (looking
> > > at this now, I should probably be taking the X value really).
> > > very initial mesa/GLSL support for the extension (completely untested).
> > > initial softpipe support for the capability a demonstration.
> > >
> > > TODO:
> > > probably stop using Y (this was just because the hw uses Y), the GLSL
> > > extension just defines an integer output for the fragprog.
> > > fix the 24/8 texstore variant.
> > > write some test code for piglit and test the GL extension/GLSL bits.
> > >
> > > I'm a lot more interested in the non-GL extension bits as it allows
> > > stencil writes to work properly on r600g.
> > A few comments.
> > Instead of using semantic name=TGSI_SEMANTIC_POSITION, index=1 to
> > indicate the stencil output, how about just defining a new
> > TGSI_SEMANTIC_STENCIL label instead? I think that'd be clearer.
> > I think the fragment stencil result is supposed to be an integer. But
> > in the softpipe changes, it looks like you're doing a [0,1]->[0,255]
> > scaling at one point.
> > If we want to use this feature for implementing glDraw/CopyPixels
> > functionality, the stencil values will be coming from a texture. How
> > do we sample that texture? That is, which components of the texture
> > image return the Z and/or stencil components? Basically, we need to
> > add a new row to the table in the tgsi.rst file for Z/Stencil
> > textures. Also, we need to clarify that fetching a stencil value
> > returns an integer value, not a float normalized to [0,1].
> DirectX 10 documentation concerning depth textures is quite peculiar,
> they suggest using typecasts:
> But they specifically mention reading z24s8 stencil values this way,
... they *don't* specifically mention ...
> although it could be certainly possible, by reading the texture as i32.
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
More information about the mesa-dev