docs: enhance blend documentation

src/gallium/docs/source/cso/blend.rst

@@ -6,9 +6,42 @@ Blend
 This state controls blending of the final fragments into the target rendering
 buffers.
 
-XXX it is unresolved what behavior should result if blend_enable is off.
-
 Members
 -------
 
-XXX undocumented members
+independent_blend_enable
+   If enabled, blend state is different for each render target, and
+   for each render target set in the respective member of the rt array.
+   If disabled, blend state is the same for all render targets, and only
+   the first member of the rt array contains valid data.
+logicop_enable
+   Enables logic ops. Cannot be enabled at the same time as blending, and
+   is always the same for all render targets.
+logicop_func
+   The logic operation to use if logic ops are enabled. One of PIPE_LOGICOP.
+dither
+   Whether dithering is enabled.
+rt
+   Contains the per rendertarget blend state.
+
+per rendertarget members
+------------------------
+
+blend_enable
+   If blending is enabled, perform a blend calculation according to blend
+   functions and source/destination factors. Otherwise, the incoming fragment
+   color gets passed unmodified (but colormask still applies).
+rgb_func
+   The blend function to use for rgb channels. One of PIPE_BLEND.
+rgb_src_factor
+   The blend source factor to use for rgb channels. One of PIPE_BLENDFACTOR.
+rgb_dst_factor
+   The blend destination factor to use for rgb channels. One of PIPE_BLENDFACTOR.
+alpha_func
+   The blend function to use for the alpha channel. One of PIPE_BLEND.
+alpha_src_factor
+   The blend source factor to use for the alpha channel. One of PIPE_BLENDFACTOR.
+alpha_dst_factor
+   The blend destination factor to use for alpha channel. One of PIPE_BLENDFACTOR.
+colormask
+   Bitmask of which channels to write. Combination of PIPE_MASK bits.