gl_ViewportIndex

In the geometry language, is used to specify the index of the viewport to which the next primitive emitted from the shader should be drawn. Primitives generated by the geometry shader will undergo viewport transformation and scissor testing using the viewport transformation and scissor rectangle selected by the value of . The viewport index used will come from one of the vertices in the primitive being shaded. However, which vertex the viewport index comes from is implementation-defined, and so it is recommended to use the same viewport index for all vertices of a primitive. If a geometry shader does not assign a value to , viewport transform and scissor rectangle zero will be used. If a geometry shader statically assigns a value to and there is a path through the shader that does not assign a value to , the value of is undefined for executions of the shader that take that path.

In the fragment language, will have the same value that was written to the output variable in the geometry stage. If the geometry stage does not dynamically assign to , the value of in the fragment shader will be undefined. If the geometry stage makes no static assignment to , the fragment stage will read zero. Otherwise, the fragment stage will read the same value written by the geometry stage, even if that value is out of range. If a fragment shader contains a static access to , it will count against the implementation defined limit for the maximum number of inputs to the fragment stage.

gl_Layer

Copyright 2011-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. .