gallium: add basic support for ARB_sample_shading

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/docs/source/context.rst

@@ -67,6 +67,7 @@ objects. They all follow simple, one-method binding calls, e.g.
   which are used as comparison values in stencil test.
 * ``set_blend_color``
 * ``set_sample_mask``
+* ``set_min_samples`` sets the minimum number of samples that must be run.
 * ``set_clip_state``
 * ``set_polygon_stipple``
 * ``set_scissor_states`` sets the bounds for the scissor test, which culls

src/gallium/docs/source/screen.rst

@@ -197,6 +197,9 @@ The integer capabilities:
   in conjunction with a texture gather opcode.
 * ``PIPE_CAP_MAX_TEXTURE_GATHER_OFFSET``: The maximum offset that can be used
   in conjunction with a texture gather opcode.
+* ``PIPE_CAP_SAMPLE_SHADING``: Whether there is support for per-sample
+  shading. The context->set_min_samples function will be expected to be
+  implemented.
 
 
 .. _pipe_capf:

src/gallium/docs/source/tgsi.rst

@@ -2621,6 +2621,26 @@ distances and by the PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT
 which specifies the maximum number of registers which can be
 annotated with those semantics.
 
+TGSI_SEMANTIC_SAMPLEID
+""""""""""""""""""""""
+
+For fragment shaders, this semantic label indicates that a system value
+contains the current sample id (i.e. gl_SampleID). Only the X value is used.
+
+TGSI_SEMANTIC_SAMPLEPOS
+"""""""""""""""""""""""
+
+For fragment shaders, this semantic label indicates that a system value
+contains the current sample's position (i.e. gl_SamplePosition). Only the X
+and Y values are used.
+
+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.
+
 
 Declaration Interpolate
 ^^^^^^^^^^^^^^^^^^^^^^^