OpenGL.GL.ATI.text_fragment_shader

OpenGL extension ATI.text_fragment_shader

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

Overview (from the spec)

The ATI_fragment_shader extension exposes a powerful fragment processing model that provides a very general means of expressing fragment color blending and dependent texture address modification. The processing is termed a fragment shader or fragment program and is specifed using a register-based model in which there are fixed numbers of instructions, texture lookups, read/write registers, and constants.

ATI_fragment_shader provides a unified instruction set for operating on address or color data and eliminates the distinction between the two. That extension provides all the interfaces necessary to fully expose this programmable fragment processor in GL.

ATI_text_fragment_shader is a redefinition of the ATI_fragment_shader functionality, using a slightly different interface. The intent of creating ATI_text_fragment_shader is to take a step towards treating fragment programs similar to other programmable parts of the GL rendering pipeline, specifically vertex programs. This new interface is intended to appear similar to the ARB_vertex_program API, within the limits of the feature set exposed by the original ATI_fragment_shader extension.

The most significant differences between the two extensions are:

(1) ATI_fragment_shader provides a procedural function call interface to specify the fragment program, whereas ATI_text_fragment_shader uses a textual string to specify the program. The fundamental syntax and constructs of the program "language" remain the same.

(2) The program object managment portions of the interface, namely the routines used to create, bind, and delete program objects and set program constants are managed using the framework defined by ARB_vertex_program.

(3) ATI_fragment_shader refers to the description of the programmable fragment processing as a "fragment shader". In keeping with the desire to treat all programmable parts of the pipeline consistently, ATI_text_fragment_shader refers to these as "fragment programs". The name of the extension is left as ATI_text_fragment_shader instead of ATI_text_fragment_program in order to indicate the underlying similarity between the API's of the two extensions, and to differentiate it from any other potential extensions that may be able to move even further in the direction of treating fragment programs as just another programmable area of the GL pipeline.

Although ATI_fragment_shader was originally conceived as a device-independent extension that would expose the capabilities of future generations of hardware, changing trends in programmable hardware have affected the lifespan of this extension. For this reason you will now find a fixed set of features and resources exposed, and the queries to determine this set have been deprecated in ATI_fragment_shader. Further, in ATI_text_fragment_shader, most of these resource limits are fixed by the text grammar and the queries have been removed altogether.

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