gallium: add TGSI_SEMANTIC_TEXCOORD,PCOORD v3

This makes it possible to identify gl_TexCoord and gl_PointCoord
for drivers where sprite coordinate replacement is restricted.

The new PIPE_CAP_TGSI_TEXCOORD decides whether these varyings
should be hidden behind the GENERIC semantic or not.

With this patch only nvc0 and nv30 will request that they be used.

v2: introduce a CAP so other drivers don't have to bother with
the new semantic

v3: adapt to introduction gl_varying_slot enum

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

@@ -159,13 +159,18 @@ Points
 
 sprite_coord_enable
 ^^^^^^^^^^^^^^^^^^^
+The effect of this state depends on PIPE_CAP_TGSI_TEXCOORD !
 
 Controls automatic texture coordinate generation for rendering sprite points.
 
+If PIPE_CAP_TGSI_TEXCOORD is false:
 When bit k in the sprite_coord_enable bitfield is set, then generic
 input k to the fragment shader will get an automatically computed
 texture coordinate.
 
+If PIPE_CAP_TGSI_TEXCOORD is true:
+The bitfield refers to inputs with TEXCOORD semantic instead of generic inputs.
+
 The texture coordinate will be of the form (s, t, 0, 1) where s varies
 from 0 to 1 from left to right while t varies from 0 to 1 according to
 the state of 'sprite_coord_mode' (see below).

src/gallium/docs/source/screen.rst

@@ -137,6 +137,14 @@ The integer capabilities:
 * ``PIPE_CAP_TEXTURE_BUFFER_OFFSET_ALIGNMENT``: Describes the required
   alignment for pipe_sampler_view::u.buf.first_element, in bytes.
   If a driver does not support first/last_element, it should return 0.
+* ``PIPE_CAP_TGSI_TEXCOORD``: This CAP describes a hw limitation.
+  If true, the hardware cannot replace arbitrary shader inputs with sprite
+  coordinates and hence the inputs that are desired to be replaceable must
+  be declared with TGSI_SEMANTIC_TEXCOORD instead of TGSI_SEMANTIC_GENERIC.
+  The rasterizer's sprite_coord_enable state therefore also applies to the
+  TEXCOORD semantic.
+  Also, TGSI_SEMANTIC_PCOORD becomes available, which labels a fragment shader
+  input that will always be replaced with sprite coordinates.
 
 
 .. _pipe_capf:

src/gallium/docs/source/tgsi.rst

@@ -1949,6 +1949,35 @@ When using this semantic, be sure to set the appropriate state in the
 :ref:`rasterizer` first.
 
 
+TGSI_SEMANTIC_TEXCOORD
+""""""""""""""""""""""
+
+Only available if PIPE_CAP_TGSI_TEXCOORD is exposed !
+
+Vertex shader outputs and fragment shader inputs may be labeled with
+this semantic to make them replaceable by sprite coordinates via the
+sprite_coord_enable state in the :ref:`rasterizer`.
+The semantic index permitted with this semantic is limited to <= 7.
+
+If the driver does not support TEXCOORD, sprite coordinate replacement
+applies to inputs with the GENERIC semantic instead.
+
+The intended use case for this semantic is gl_TexCoord.
+
+
+TGSI_SEMANTIC_PCOORD
+""""""""""""""""""""
+
+Only available if PIPE_CAP_TGSI_TEXCOORD is exposed !
+
+Fragment shader inputs may be labeled with TGSI_SEMANTIC_PCOORD to indicate
+that the register contains sprite coordinates in the form (x, y, 0, 1), if
+the current primitive is a point and point sprites are enabled. Otherwise,
+the contents of the register are undefined.
+
+The intended use case for this semantic is gl_PointCoord.
+
+
 TGSI_SEMANTIC_GENERIC
 """""""""""""""""""""