tgsi: clarify TGSI_SEMANTIC_SAMPLEMASK documentation

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
index eceaa6d..7fb963f 100644 (file)
--- a/src/gallium/docs/source/tgsi.rst
+++ b/src/gallium/docs/source/tgsi.rst
@@ -3298,8 +3298,9 @@ TGSI_SEMANTIC_SAMPLEMASK
 """"""""""""""""""""""""
 
 For fragment shaders, this semantic label indicates that an output contains
-the sample mask used to disable further sample processing
-(i.e. gl_SampleMask). Only the X value is used, up to 32x MS.
+the sample mask used to disable further sample processing.  The output's
+type is uint[4] but only the X component is used (i.e. gl_SampleMask[0]).
+Each bit corresponds to one sample position (up to 32x MSAA is supported).
 
 TGSI_SEMANTIC_INVOCATIONID
 """"""""""""""""""""""""""