On Mon, Jan 9, 2012 at 5:06 PM, Brian Paul <bri...@vmware.com> wrote: > On 01/09/2012 06:35 AM, Dave Airlie wrote: >> >> Okay so we have a gallium/GL/GLSL problem with interpolation, lets see >> if I can describe the issue: >> >> In the beginning there was GL interpolation rules, glShadeModel was >> the only information you had. >> >> Then came GLSL which allowed overriding the GL defaults using specifiers. >> >> So the gl_FrontColor variant, if left unspecified would take the value >> of the glShadeModel, if specified >> it would over-rule the current ShadeModel setting. >> >> >> So we end up something like this >> >> if (glFrontColor attrib> 0) result = glFrontColor_attrib; else result >> = shademodel. >> >> Now when we convert to gallium we lose the unspecified interpolation, >> and we generate a default interpolation >> attribute, which should usually be SMOOTH. Now we've no idea then >> inside the gallium drivers whether this smooth >> is due to an explicit smooth at the GLSL level which we can't >> override, or whether this smooth is something that we really >> wanted to be overruled by the ShadeModel bit. >> >> Now as discussed previously most hardware has support for the >> ShadeModel bit so generating multiple shaders >> for the unspecified case would be suboptimal for it. >> >> So the options I see are: >> >> (a) do it anyways, apply the patch I had earlier that derives the >> setting at the glsl->tgsi translation stage, and pretty >> much ignore it. >> >> (b) add unspecified interpolation support for Color inputs, only >> colors are affected by this, and since TGSI supports >> Colors we should probably support all the features of the GL Color >> output/inputs. >> >> Anyone any other ideas? > > > I'd probably go with (b), add a new TGSI_INTERPOLATE_COLOR mode that means > "look at pipe_rasterizer_state::flatshade." > > IMO, it's still attractive to get rid of pipe_rasterizer_state::flatshade > someday. glShadeModel no longer exists in OpenGL 3.2 core profile and > later.
Please note that the GLSL interpolation modes are a GLSL 1.3 feature. We can't remove pipe_rasterizer_state::flatshade_first for non-GL3 drivers. And even with the interpolation modes available, recompiling.shaders when glShadeModel changes is an anti-optimization if drivers can do pipe_rasterizer_state::flatshade_first just fine. I would prefer that if there's a driver which cannot do pipe_rasterizer_state::flatshade_first (just svga?), let's add a CAP for it and handle it in the state tracker. Marek _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
