OpenGL.GL.AMD.vertex_shader_tessellator

OpenGL extension AMD.vertex_shader_tessellator

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

Overview (from the spec)

The vertex shader tessellator gives new flexibility to the shader author to shade at a tessellated vertex, rather than just at a provided vertex.

In unextended vertex shading, the built-in attributes such as gl_Vertex, gl_Normal, and gl_MultiTexcoord0, together with the user defined attributes, are system provided values which are initialized prior to vertex shader invocation.

With vertex shading tessellation, additional vertex shader special values are available:

ivec3 gl_VertexTriangleIndex; // indices of the three control // points for the vertex vec3 gl_BarycentricCoord; // barycentric coordinates // of the vertex

i o | | *--* |\ | | \| *--*--* |\ |\ | | \| \| j o--*--*--o k

Figure 1 A Tessellated Triangle o = control point (and tessellated vertex) * = tessellated vertex

ivec4 gl_VertexQuadIndex; // indices for the four control // points for the vertex vec2 gl_UVCoord; // UV coordinates of the vertex

i o--*--*--o k |\ |\ |\ | | \| \| \| *--*--*--* |\ |\ |\ | | \| \| \| *--*--*--* |\ |\ |\ | | \| \| \| j o--*--*--o l

Figure 2 A Tessellated Quad o = control point (and tessellated vertex) * = tessellated vertex

When this extension is enabled, conventional built-in attributes and user defined attributes are uninitialized. The shader writer is responsible for explicitly fetching all other vertex data either from textures, uniform buffers, or vertex buffers.

The shader writer is further responsible for interpolating the vertex data at the given barycentric coordinates or uv coordinates of the vertex.

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