gallium/docs: document behavior of set_sample_mask()

The sample mask is used even if msaa is not explicity enabled when we
have a framebuffer with multisampled surfaces.  That's DX behavior and
what the Radeon drivers do.  Not sure about other drivers at this point.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

diff --git a/src/gallium/docs/source/context.rst b/src/gallium/docs/source/context.rst
index 9d069b3..0ac7340 100644 (file)
--- a/src/gallium/docs/source/context.rst
+++ b/src/gallium/docs/source/context.rst
@@ -64,7 +64,10 @@ objects. They all follow simple, one-method binding calls, e.g.
 * ``set_stencil_ref`` sets the stencil front and back reference values
   which are used as comparison values in stencil test.
 * ``set_blend_color``
-* ``set_sample_mask``
+* ``set_sample_mask``  sets the per-context multisample sample mask.  Note
+  that this takes effect even if multisampling is not explicitly enabled if
+  the frambuffer surface(s) are multisampled.  Also, this mask is AND-ed
+  with the optional fragment shader sample mask output (when emitted).
 * ``set_min_samples`` sets the minimum number of samples that must be run.
 * ``set_clip_state``
 * ``set_polygon_stipple``