----- Original Message ----- > On 12/13/2011 03:09 PM, Jose Fonseca wrote: > > > > ----- Original Message ----- > >> On 12/13/2011 12:26 PM, Bryan Cain wrote: > >>> On 12/13/2011 02:11 PM, Jose Fonseca wrote: > >>>> ----- Original Message ----- > >>>>> This is an updated version of the patch set I sent to the list > >>>>> a > >>>>> few > >>>>> hours > >>>>> ago. > >>>>> There is now a TGSI property called > >>>>> TGSI_PROPERTY_NUM_CLIP_DISTANCES > >>>>> that drivers can use to determine how many of the 8 available > >>>>> clip > >>>>> distances > >>>>> are actually used by a shader. > >>>> Can't the info in TGSI_PROPERTY_NUM_CLIP_DISTANCES be easily > >>>> derived from the shader, and queried through > >>>> src/gallium/auxiliary/tgsi/tgsi_scan.h ? > >>> No. The clip distances can be indirectly addressed (there are up > >>> to 2 > >>> of them in vec4 form for a total of 8 floats), which makes it > >>> impossible > >>> to determine which ones are used by analyzing the shader. > >> The description is almost complete. :) The issue is that the > >> shader > >> may > >> declare > >> > >> out float gl_ClipDistance[4]; > >> > >> the use non-constant addressing of the array. The compiler knows > >> that > >> gl_ClipDistance has at most 4 elements, but post-hoc analysis > >> would > >> not > >> be able to determine that. Often the fixed-function hardware (see > >> below) needs to know which clip distance values are actually > >> written. > > But don't all the clip distances written by the shader need to be > > declared? > > > > E.g.: > > > > DCL OUT[0], CLIPDIST[0] > > DCL OUT[1], CLIPDIST[1] > > DCL OUT[2], CLIPDIST[2] > > DCL OUT[3], CLIPDIST[3] > > > > therefore a trivial analysis of the declarations convey that? > > No. Clip distance is an array of up to 8 floats in GLSL, but it's > represented in the hardware as 2 vec4s. You can tell by analyzing > the > declarations whether there are more than 4 clip distances in use, but > not which components the shader writes to. > TGSI_PROPERTY_NUM_CLIP_DISTANCES is the number of components in use, > not > the number of full vectors.
Lets imagine out float gl_ClipDistance[6]; Each a clip distance is a scalar float. Either all hardware represents the 8 clip distances as two 4 vectors, and we do: DCL OUT[0].xywz, CLIPDIST[0] DCL OUT[1].xy, CLIPDIST[1] using the full range of struct tgsi_declaration::UsageMask [1] or we represent them as as scalars: DCL OUT[0].x, CLIPDIST[0] DCL OUT[1].x, CLIPDIST[1] DCL OUT[2].x, CLIPDIST[2] DCL OUT[3].x, CLIPDIST[3] DCL OUT[4].x, CLIPDIST[4] DCL OUT[5].x, CLIPDIST[5] If indirect addressing is allowed as I read bore, then maybe the later is better. I confess my ignorance about clipping and maybe I'm being dense, but I still don't see the need for this TGSI_PROPERTY_NUM_CLIP_DISTANCES. Could you please draft an example TGSI shader showing this property (or just paste one generated with your change)? I think that would help a lot. Jose [1] I don't know if tgsi_dump pays much attention to tgsi_declaration::UsageMask, but it does exist. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
