On 22 May 2012 10:15, Ian Romanick <i...@freedesktop.org> wrote: > On 05/21/2012 07:16 PM, Paul Berry wrote: > >> On 21 May 2012 18:00, Ian Romanick <i...@freedesktop.org >> <mailto:i...@freedesktop.org>> wrote: >> >> On 05/11/2012 11:03 AM, Paul Berry wrote: >> >> This patch modifies the "blorp" WM program so that it can be run in >> MSDISPMODE_PERSAMPLE (which means that every single sample of a >> multisampled render target is dispatched to the WM program, not >> just >> every pixel). >> >> Previously we were using the ugly hack of configuring multisampled >> destination surfaces as single-sampled, and generating sample >> indices >> other than zero by swizzling the pixel coordinates in the WM >> program. >> --- >> src/mesa/drivers/dri/i965/brw_**__blorp.h | 12 ++++ >> src/mesa/drivers/dri/i965/brw_**__blorp_blit.cpp | 87 >> +++++++++++++++++++------- >> src/mesa/drivers/dri/i965/__**gen6_blorp.cpp | 5 +- >> src/mesa/drivers/dri/i965/__**gen7_blorp.cpp | 10 ++- >> >> 4 files changed, 87 insertions(+), 27 deletions(-) >> >> diff --git a/src/mesa/drivers/dri/i965/__**brw_blorp.h >> b/src/mesa/drivers/dri/i965/__**brw_blorp.h >> index f14a5c7..b911356 100644 >> --- a/src/mesa/drivers/dri/i965/__**brw_blorp.h >> +++ b/src/mesa/drivers/dri/i965/__**brw_blorp.h >> >> @@ -132,6 +132,12 @@ const unsigned int >> BRW_BLORP_NUM_PUSH_CONST_REGS = >> struct brw_blorp_prog_data >> { >> unsigned int first_curbe_grf; >> + >> + /** >> + * True if the WM program should be run in >> MSDISPMODE_PERSAMPLE with more >> + * than one sample per pixel. >> + */ >> + bool persample_msaa_dispatch; >> >> >> (Forgive my ignorance about this general area of the code.) >> Per-sample shading is also a feature of some later OpenGL version. >> Is the low-level infrastructure architected so that we could >> enable this for general use? >> >> >> This patch wouldn't get in the way of enabling per-sample shading for >> general use, but it wouldn't really facilitate it either, since this is >> just using per-sample shading for blits. >> >> Enabling per-sample shading for general use should be pretty >> straightforward. If I'm not mistaken, all we will need to do is: >> >> - Add the front-end API to allow the client to request per-sample >> shading (I assume it's glEnable(GL_HAM_SANDWICH) or something like that, >> in which case it should be easy) >> >> - Set the MSDISPMODE_PERSAMPLE bit gen{6,7}_wm_state.c (easy). >> >> - Modify the code that configures barycentric interpolation modes so >> that we can interpolate smooth and noperspective varyings to the sample >> location rather than to the pixel center or the centroid. This will be >> the hardest part, because it will require modifying the fragment shader >> back-end interpolation code to point to the appropriate barycentric >> coordinates depending whether per-sample shading is enabled or not. But >> I already had to make a similar change to implement the "flat" keyword, >> and I'll have to do something similar very soon for "centroid", so I'm >> not terribly worried. I'll try to keep this feature in mind when I'm >> implementing "centroid" so that I don't paint us into a corner. >> >> If time allows, I might could roll this feature in with implementing >> "centroid", but I won't make any guarantees because I don't want to >> delay centroid interpolation at the expense of a future feature. Would >> you mind pointing me to the relevant text in the GL spec so that I can >> read up on it and make sure I'm not missing any subtleties? >> > > Olivier hit most of the high points. The spec is: > > http://www.opengl.org/**registry/specs/ARB/sample_**shading.txt<http://www.opengl.org/registry/specs/ARB/sample_shading.txt> >
Thanks for the ref. Looking at the spec, it looks like there would be a bit more work to do to fully implement the extension: - Add the gl_SampleID variable to GLSL, and write back-end code to populate it (should be fairly straightforward) - Add the gl_SamplePosition variable to GLSL, and write back-end code to populate it (a bit more work; I think we have to set some additional flags in 3DSTATE_WM to get this info) - Add the gl_SampleMask[] variable to GLSL, and write back-end support for it (ugh, this is going to require some tricky bit swizzling I think*) - Add the gl_NumSamples mask to GLSL, and write back-end support for it (a bit of work since I'm less familiar with how uniforms work) *However, it's possible that I'm going to need to do a lot of this work anyway to implement the alpha-to-coverage stuff. On balance I no longer think it's worth trying to roll this extension in with the initial MSAA implementation. There's just a bit too much work to do. Also, this extension will be *a lot* easier to test after we've implemented ARB_texture_multisample, because ARB_texture_multisample gives the ability for client programs to directly query individual samples. So I'm going to back burner ARB_sample_shading for now.
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