OpenGL. GL. ARB. fragment_program

OpenGL extension ARB.fragment_program

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

Overview (from the spec)

Unextended OpenGL mandates a certain set of configurable per- fragment computations defining texture application, texture environment, color sum, and fog operations. Several extensions have added further per-fragment computations to OpenGL. For example, extensions have defined new texture environment capabilities (ARB_texture_env_add, ARB_texture_env_combine, ARB_texture_env_dot3, ARB_texture_env_crossbar), per-fragment depth comparisons (ARB_depth_texture, ARB_shadow, ARB_shadow_ambient, EXT_shadow_funcs), per-fragment lighting (EXT_fragment_lighting, EXT_light_texture), and environment mapped bump mapping (ATI_envmap_bumpmap).

Each such extension adds a small set of relatively inflexible per- fragment computations.

This inflexibility is in contrast to the typical flexibility provided by the underlying programmable floating point engines (whether micro-coded fragment engines, DSPs, or CPUs) that are traditionally used to implement OpenGL's texturing computations. The purpose of this extension is to expose to the OpenGL application writer a significant degree of per-fragment programmability for computing fragment parameters.

For the purposes of discussing this extension, a fragment program is a sequence of floating-point 4-component vector operations that determines how a set of program parameters (not specific to an individual fragment) and an input set of per-fragment parameters are transformed to a set of per-fragment result parameters.

The per-fragment computations for standard OpenGL given a particular set of texture and fog application modes (along with any state for extensions defining per-fragment computations) is, in essence, a fragment program. However, the sequence of operations is defined implicitly by the current OpenGL state settings rather than defined explicitly as a sequence of instructions.

This extension provides an explicit mechanism for defining fragment program instruction sequences for application-defined fragment programs. In order to define such fragment programs, this extension defines a fragment programming model including a floating-point 4-component vector instruction set and a relatively large set of floating-point 4-component registers.

The extension's fragment programming model is designed for efficient hardware implementation and to support a wide variety of fragment 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 fragment programming model.

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