On 04/05/16 12:31, Kenneth Graunke wrote: > On Thursday, April 28, 2016 1:40:31 PM PDT Antia Puentes wrote: >> From: Alejandro Piñeiro <apinhe...@igalia.com> >> >> This commit adds support for PASSTHRU format when pushing >> double-precision attributes. >> >> Check glarray->Doubles in order to know if we should choose a format >> that does a conversion to float, or just passthru the 64-bit double. >> --- >> src/mesa/drivers/dri/i965/brw_draw_upload.c | 30 +++++++++++++++++++++++++ > +--- >> 1 file changed, 27 insertions(+), 3 deletions(-) > What's the motivation for using the PASSTHRU formats? Is there some > advantage over just using the R64*FLOAT formats?
We can't use R64*FLOAT because it does a double to float conversion, as explained at the bdw PRM (vol 7, section 10.15, page 470, Table "Source Element Formats Supported in VF Unit"). PASSTHRU ensures that the 64-bits are passed without any conversion, that is what we want. If it is not clear reading the commit message, I could expand it. FWIW, the R64*FLOAT format is used when calling the previous API (without *L*). You can call glVertexAttribPointer using GL_DOUBLE as type, but it will feed the shaders with floats. That conversion is done using R64*FLOAT formats when uploading the data. When using glVertexAttrib with GL_DOUBLE, the casting to float is done on the call itself, at mesa/main. Finally, the alternative to R64*PASSTHRU formats would be using R32*FLOAT formats, and doing two uploads if needed (for dvec3/dvec4). We needed to do that for the in-progress gen7 support, and means some extra code compared to just use PASSTHRU. If you are curious: https://github.com/Igalia/mesa/commit/7d4b0c5cff33a3b555a9c5d38b1af0aeba697cac Best regards _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
