OpenGL.GL.EXT.separate_shader_objects

OpenGL extension EXT.separate_shader_objects

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

Overview (from the spec)

Prior to this extension, GLSL requires multiple shader domains (vertex, fragment, geometry) to be linked into a single monolithic program object to specify a GLSL shader for each domain.

While GLSL's monolithic approach has some advantages for optimizing shaders as a unit that span multiple domains, all existing GPU hardware supports the more flexible mix-and-match approach.

HLSL9, Cg, the prior OpenGL assembly program extensions, and game console programmers favor a more flexible "mix-and-match" approach to specifying shaders independently for these different shader domains. Many developers build their shader content around the mix-and-match approach where they can use a single vertex shader with multiple fragment shaders (or vice versa).

This keep-it-simple extension adapts the "mix-and-match" shader domain model for GLSL so different GLSL program objects can be bound to different shader domains.

This extension redefines the operation of glUseProgram(GLenum program) to be equivalent to:

glUseShaderProgramEXT(GL_VERTEX_SHADER, program); glUseShaderProgramEXT(GL_GEOMETRY_SHADER_EXT, program); glUseShaderProgramEXT(GL_FRAGMENT_SHADER, program); glActiveProgramEXT(program);

You can also call these commands separately to bind each respective domain. The GL_VERTEX_SHADER, GL_GEOMETRY_SHADER_EXT, and GL_FRAGMENT_SHADER tokens refer to the conventional vertex, geometry, and fragment domains respectively. glActiveProgramEXT specifies the program that glUniform* commands will update.

Separate linking creates the possibility that certain output varyings of a shader may go unread by the subsequent shader inputting varyings. In this case, the output varyings are simply ignored. It is also possible input varyings from a shader may not be written as output varyings of a preceding shader. In this case, the unwritten input varying values are undefined. Implementations are encouraged to zero these undefined input varying values.

This extension is a proof-of-concept that separate shader objects can work for GLSL and a response to repeated requests for this functionality. There are various loose ends, particularly when dealing with user-defined varyings. The hope is a future extension will improve this situation.

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