gl_Position

In the vertex, tessellation evaluation and geometry languages, a single global instance of the named block is available and its member is an output that receives the homogeneous vertex position. It may be written at any time during shader execution. The value written to will be used by primitive assembly, clipping, culling and other fixed functionality operations, if present, that operate on primitives after vertex processing has occurred.

In the tessellation control language, the named block is used to construct an array, , whose members hold the homogeneous control point position, which become available as inputs to the subsequent tessellation evaluation shader.

The value of (or the member of the array, in the case of the tessellation control shader) is undefined after the vertex, tessellation control, and tessellation evaluation shading stages if the corresponding shader executable does not write to gl_Position. It is also undefined after the geometry processing stage if the geometry shader executable calls EmitVertex without having written since the last call to EmitVertex (or hasn't written it at all).

In the tessellation control, tessellation evaluation and geometry languages, the named block is used to construct an array, of per-vertex or per-control point inputs whose content represents the corresponding outputs written by the previous stage.

Versions 1.10 to 1.40 - vertex shader only.

Versions 1.50 to 3.30 - vertex and geometry shaders only.

gl_PointSize , gl_ClipDistance

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