From: Ian Romanick <ian.d.roman...@intel.com> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com> Cc: "10.2" <mesa-sta...@lists.freedesktop.org> --- src/mesa/main/mtypes.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+)
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h index 3899e7f..34e66c9 100644 --- a/src/mesa/main/mtypes.h +++ b/src/mesa/main/mtypes.h @@ -2039,7 +2039,55 @@ typedef enum * \name Vertex shader system values */ /*@{*/ + /** + * OpenGL-style vertex ID. + * + * Section 2.11.7 (Shader Execution), subsection Shader Inputs, of the + * OpenGL 3.3 core profile spec says: + * + * "gl_VertexID holds the integer index i implicitly passed by + * DrawArrays or one of the other drawing commands defined in section + * 2.8.3." + * + * Section 2.8.3 (Drawing Commands) of the same spec says: + * + * "The commands....are equivalent to the commands with the same base + * name (without the BaseVertex suffix), except that the ith element + * transferred by the corresponding draw call will be taken from + * element indices[i] + basevertex of each enabled array." + * + * gl_VertexID gets basevertex added in. This differs from DirectX where + * it's equivalent to gl_VertexID does \b not get basevertex added in. + */ SYSTEM_VALUE_VERTEX_ID, + + /** + * Instanced ID as supplied to gl_InstanceID + * + * Values assigned to gl_InstanceID always begin with zero, regardless of + * the value of baseinstance. + * + * Section 11.1.3.9 (Shader Inputs) of the OpenGL 4.4 core profile spec + * says: + * + * "gl_InstanceID holds the integer instance number of the current + * primitive in an instanced draw call (see section 10.5)." + * + * Through a big chain of pseudocode, section 10.5 describes that + * baseinstance is not counted by gl_InstanceID. In that section, notice + * + * "If an enabled vertex attribute array is instanced (it has a + * non-zero divisor as specified by VertexAttribDivisor), the element + * index that is transferred to the GL, for all vertices, is given by + * + * floor(instance/divisor) + baseinstance + * + * If an array corresponding to an attribute required by a vertex + * shader is not enabled, then the corresponding element is taken from + * the current attribute state (see section 10.2)." + * + * Note that baseinstance is \b not included in the value of instance. + */ SYSTEM_VALUE_INSTANCE_ID, /*@}*/ -- 1.8.1.4 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev