OpenGL.GL.NV.fragment_program

OpenGL extension NV.fragment_program

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

Overview (from the spec)

OpenGL mandates a certain set of configurable per-fragment computations defining texture lookup, texture environment, color sum, and fog operations. Each of these areas provide a useful but limited set of fixed operations. For example, unextended OpenGL 1.2.1 provides only four texture environment modes, color sum, and three fog modes. Many OpenGL extensions have either improved existing functionality or introduced new configurable fragment operations. While these extensions have enabled new and interesting rendering effects, the set of effects is limited by the set of special modes introduced by the extension. This lack of flexibility is in contrast to the high-level of programmability of general-purpose CPUs and other (frequently software-based) shading languages. The purpose of this extension is to expose to the OpenGL application writer an unprecedented degree of programmability in the computation of final fragment colors and depth values.

This extension provides a mechanism for defining fragment program instruction sequences for application-defined fragment programs. When in fragment program mode, a program is executed each time a fragment is produced by rasterization. The inputs for the program are the attributes (position, colors, texture coordinates) associated with the fragment and a set of constant registers. A fragment program can perform mathematical computations and texture lookups using arbitrary texture coordinates. The results of a fragment program are new color and depth values for the fragment.

This extension defines a programming model including a 4-component vector instruction set, 16- and 32-bit floating-point data types, and a relatively large set of temporary registers. The programming model also includes a condition code vector which can be used to mask register writes at run-time or kill fragments altogether. The syntax, program instructions, and general semantics are similar to those in the NV_vertex_program and NV_vertex_program2 extensions, which provide for the execution of an arbitrary program each time the GL receives a vertex.

The fragment program execution environment is designed for efficient hardware implementation and to support a wide variety of programs. By design, the entire set of existing fragment programs defined by existing OpenGL per-fragment computation extensions can be implemented using the extension's programming model.

The fragment program execution environment accesses textures via arbitrarily computed texture coordinates. As such, there is no necessary correspondence between the texture coordinates and texture maps previously lumped into a single "texture unit". This extension separates the notion of "texture coordinate sets" and "texture image units" (texture maps and associated parameters), allowing implementations with a different number of each. The initial implementation of this extension will support 8 texture coordinate sets and 16 texture image units.

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