# OpenGL.GL.AMD.vertex_shader_viewport_index

OpenGL extension AMD.vertex_shader_viewport_index

This module customises the behaviour of the
OpenGL.raw.GL.AMD.vertex_shader_viewport_index to provide a more
Python-friendly API

Overview (from the spec)

The gl_ViewportIndex built-in variable was introduced by the
ARB_viewport_array extension and OpenGL 4.1. This variable is available
in un-extended OpenGL only to the geometry shader. When written in the
geometry shader, it causes geometry to be directed to one of an array
of several independent viewport rectangles.

In order to use any viewport other than zero, a geometry shader must be
present. Geometry shaders introduce processing overhead and potential
performance issues. This extension exposes the gl_ViewportIndex built-in
variable to the vertex shader, allowing the functionality introduced by
ARB_viewport_array to be accessed without requiring a geometry shader to
be present.

The official definition of this extension is available here:
http://www.opengl.org/registry/specs/AMD/vertex_shader_viewport_index.txt