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-rw-r--r--src/gallium/docs/source/tgsi.rst55
1 files changed, 33 insertions, 22 deletions
diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
index 205e7b8539d..e588c5b7bd8 100644
--- a/src/gallium/docs/source/tgsi.rst
+++ b/src/gallium/docs/source/tgsi.rst
@@ -1286,6 +1286,8 @@ wrapping rules.
Declaration Semantic
^^^^^^^^^^^^^^^^^^^^^^^^
+ Vertex and fragment shader input and output registers may be labeled
+ with semantic information consisting of a name and index.
Follows Declaration token if Semantic bit is set.
@@ -1321,6 +1323,10 @@ The Z coordinate ranges from 0 to 1 to represent depth from the front
to the back of the Z buffer. The W component contains the reciprocol
of the interpolated vertex position W component.
+Fragment shaders may also declare an output register with
+TGSI_SEMANTIC_POSITION. Only the Z component is writable. This allows
+the fragment shader to change the fragment's Z position.
+
TGSI_SEMANTIC_COLOR
@@ -1350,49 +1356,54 @@ so all BCOLORs effectively become regular COLORs in the fragment shader.
TGSI_SEMANTIC_FOG
"""""""""""""""""
-The fog coordinate historically has been used to replace the depth coordinate
-for generation of fog in dedicated fog blocks. Gallium, however, does not use
-dedicated fog acceleration, placing it entirely in the fragment shader
-instead.
+Vertex shader inputs and outputs and fragment shader inputs may be
+labeled with TGSI_SEMANTIC_FOG to indicate that the register contains
+a fog coordinate in the form (F, 0, 0, 1). Typically, the fragment
+shader will use the fog coordinate to compute a fog blend factor which
+is used to blend the normal fragment color with a constant fog color.
+
+Only the first component matters when writing from the vertex shader;
+the driver will ensure that the coordinate is in this format when used
+as a fragment shader input.
-The fog coordinate should be written in ``(f, 0, 0, 1)`` format. Only the first
-component matters when writing from the vertex shader; the driver will ensure
-that the coordinate is in this format when used as a fragment shader input.
TGSI_SEMANTIC_PSIZE
"""""""""""""""""""
-PSIZE, or point size, is used to specify point sizes per-vertex. It should
-be in ``(s, 0, 0, 1)`` format, where ``s`` is the (possibly clamped) point size.
-Only the first component matters when writing from the vertex shader.
+Vertex shader input and output registers may be labeled with
+TGIS_SEMANTIC_PSIZE to indicate that the register contains a point size
+in the form (S, 0, 0, 1). The point size controls the width or diameter
+of points for rasterization. This label cannot be used in fragment
+shaders.
When using this semantic, be sure to set the appropriate state in the
:ref:`rasterizer` first.
+
TGSI_SEMANTIC_GENERIC
"""""""""""""""""""""
-Generic semantics are nearly always used for texture coordinate attributes,
-in ``(s, t, r, q)`` format. ``t`` and ``r`` may be unused for certain kinds
-of lookups, and ``q`` is the level-of-detail bias for biased sampling.
+All vertex/fragment shader inputs/outputs not labeled with any other
+semantic label can be considered to be generic attributes. Typical
+uses of generic inputs/outputs are texcoords and user-defined values.
-These attributes are called "generic" because they may be used for anything
-else, including parameters, texture generation information, or anything that
-can be stored inside a four-component vector.
TGSI_SEMANTIC_NORMAL
""""""""""""""""""""
-Vertex normal; could be used to implement per-pixel lighting for legacy APIs
-that allow mixing fixed-function and programmable stages.
+Indicates that a vertex shader input is a normal vector. This is
+typically only used for legacy graphics APIs.
+
TGSI_SEMANTIC_FACE
""""""""""""""""""
-FACE is the facing bit, to store the facing information for the fragment
-shader. ``(f, 0, 0, 1)`` is the format. The first component will be positive
-when the fragment is front-facing, and negative when the component is
-back-facing.
+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.
+
TGSI_SEMANTIC_EDGEFLAG
""""""""""""""""""""""