Geometry Shader

A Geometry Shader (GS) is a Shader program that governs the processing of primitives. It happens after primitive assembly, as an additional optional step in that part of the pipeline. A GS can create new primitives, unlike vertex shaders, which are limited to a 1:1 input to output ratio. A GS can also do layered rendering; this means that the GS can specifically say that a primitive is to be rendered to a particular layer of the framebuffer.

Unlike other shader stages, a GS does not have to be used.