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. Bryan _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
