gl_PrimitiveID — contains the index of the current primitive
// In tessellation control, tessellation evaluation, and // fragment shaders
in int gl_PrimitiveID ;
// In geometry shaders
out int gl_PrimitiveID ;
gl_PrimitiveID is a tessellation control, tessellation evaluation
and fragment language input variable. For the tessellation control and tessellation
evaluation languages, it holds the number of primitives processed by
the shader since the current set of rendering primitives was started. The first
primitive processed by the drawing command is numbered zero and the primitive ID counter is incremented after every individual point, line
or triangle primitive is processed. For triangles drawn in point or line mode, the
primitive ID counter is incremented only once, even through multiple points or lines
may actually be drawn. Restarting a primitive topology using the primitive restart
index has no effect on the primitive ID counter.
In the geometry language,
gl_PrimitiveID is an output
variable that is passed to the corresponding
variable in the fragment shader. If no geomery shader is present then
in the fragment language behaves identically as it would in the tessellation control and evaluation
languages. If a geometry shader is present but does not write to
the value of
gl_PrimitiveID in the fragment shader is undefined.
|OpenGL Shading Language Version|
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