gallium: add caps for POSITION and FACE system values

v2: document the integer behavior

Reviewed-by: Edward O'Callaghan <[email protected]
Reviewed-by: Brian Paul <[email protected]>

2 files changed, 18 insertions, 6 deletions

diff --git a/src/gallium/docs/source/screen.rst b/src/gallium/docs/source/screen.rst
index 39ecc6334eb..fc08bb9ac34 100644
--- a/src/gallium/docs/source/screen.rst
+++ b/src/gallium/docs/source/screen.rst
@@ -292,6 +292,11 @@ The integer capabilities:
   supported in vertex shaders.
 * ``PIPE_CAP_TGSI_PACK_HALF_FLOAT``: Whether the ``UP2H`` and ``PK2H``
   TGSI opcodes are supported.
+* ``PIPE_CAP_TGSI_FS_POSITION_IS_SYSVAL``: If state trackers should use
+  a system value for the POSITION fragment shader input.
+* ``PIPE_CAP_TGSI_FS_FACE_IS_INTEGER_SYSVAL``: If state trackers should use
+  a system value for the FACE fragment shader input.
+  Also, the FACE system value is integer, not float.
 
 
 .. _pipe_capf:
diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
index 2149d08419a..8fe971b2f7a 100644
--- a/src/gallium/docs/source/tgsi.rst
+++ b/src/gallium/docs/source/tgsi.rst
@@ -2658,7 +2658,8 @@ space coordinate system.  After clipping, the X, Y and Z components of the
 vertex will be divided by the W value to get normalized device coordinates.
 
 For fragment shaders, TGSI_SEMANTIC_POSITION is used to indicate that
-fragment shader input contains the fragment's window position.  The X
+fragment shader input (or system value, depending on which one is
+supported by the driver) contains the fragment's window position.  The X
 component starts at zero and always increases from left to right.
 The Y component starts at zero and always increases but Y=0 may either
 indicate the top of the window or the bottom depending on the fragment
@@ -2770,11 +2771,17 @@ typically only used for legacy graphics APIs.
 TGSI_SEMANTIC_FACE
 """"""""""""""""""
 
-This label applies to fragment shader inputs only and indicates that
-the register contains front/back-face information of the form (F, 0,
-0, 1).  The first component will be positive when the fragment belongs
-to a front-facing polygon, and negative when the fragment belongs to a
-back-facing polygon.
+This label applies to fragment shader inputs (or system values,
+depending on which one is supported by the driver) and indicates that
+the register contains front/back-face information.
+
+If it is an input, it will be a floating-point vector in the form (F, 0, 0, 1),
+where F will be positive when the fragment belongs to a front-facing polygon,
+and negative when the fragment belongs to a back-facing polygon.
+
+If it is a system value, it will be an integer vector in the form (F, 0, 0, 1),
+where F is 0xffffffff when the fragment belongs to a front-facing polygon and
+0 when the fragment belongs to a back-facing polygon.
 
 
 TGSI_SEMANTIC_EDGEFLAG