glUseProgram
3G

# glUseProgram

Installs a program object as part of current rendering state

## C Specification

    		void glUseProgram
    		GLuint program

## Parameters

`program`

  Specifies the handle of the program object whose executables are to be used as part of current rendering state.

## Description

`glUseProgram` installs the program object specified by `program` as part of current rendering state. One or more executables are created in a program object by successfully attaching shader objects to it with glAttachShader, successfully compiling the shader objects with glCompileShader, and successfully linking the program object with glLinkProgram.

A program object will contain an executable that will run on the vertex processor if it contains one or more shader objects of type `GL_VERTEX_SHADER` that have been successfully compiled and linked. Similarly, a program object will contain an executable that will run on the fragment processor if it contains one or more shader objects of type `GL_FRAGMENT_SHADER` that have been successfully compiled and linked.

Successfully installing an executable on a programmable processor will cause the corresponding fixed functionality of OpenGL to be disabled. Specifically, if an executable is installed on the vertex processor, the OpenGL fixed functionality will be disabled as follows.

- The modelview matrix is not applied to vertex coordinates.

- The projection matrix is not applied to vertex coordinates.

- The texture matrices are not applied to texture coordinates.

- Normals are not transformed to eye coordinates.

- Normals are not rescaled or normalized.

- Normalization of `GL_AUTO_NORMAL` evaluated normals is not performed.

- Texture coordinates are not generated automatically.

- Per-vertex lighting is not performed.

- Color material computations are not performed.

- Color index lighting is not performed.

- This list also applies when setting the current raster position.

The executable that is installed on the vertex processor is expected to implement any or all of the desired functionality from the preceding list. Similarly, if an executable is installed on the fragment processor, the OpenGL fixed functionality will be disabled as follows.

- Texture environment and texture functions are not applied.

- Texture application is not applied.

- Color sum is not applied.

- Fog is not applied.

Again, the fragment shader that is installed is expected to implement any or all of the desired functionality from the preceding list.

While a program object is in use, applications are free to modify attached shader objects, compile attached shader objects, attach additional shader objects, and detach or delete shader objects. None of these operations will affect the executables that are part of the current state. However, relinking the program object that is currently in use will install the program object as part of the current rendering state if the link operation was successful (see glLinkProgram ). If the program object currently in use is relinked unsuccessfully, its link status will be set to `GL_FALSE`, but the executables and associated state will remain part of the current state until a subsequent call to `glUseProgram` removes it from use. After it is removed from use, it cannot be made part of current state until it has been successfully relinked.

If `program` contains shader objects of type `GL_VERTEX_SHADER` but it does not contain shader objects of type `GL_FRAGMENT_SHADER`, an executable will be installed on the vertex processor, but fixed functionality will be used for fragment processing. Similarly, if `program` contains shader objects of type `GL_FRAGMENT_SHADER` but it does not contain shader objects of type `GL_VERTEX_SHADER`, an executable will be installed on the fragment processor, but fixed functionality will be used for vertex processing. If `program` is 0, the programmable processors will be disabled, and fixed functionality will be used for both vertex and fragment processing.

## Notes

`glUseProgram` is available only if the GL version is 2.0 or greater.

While a program object is in use, the state that controls the disabled fixed functionality may also be updated using the normal OpenGL calls.

Like display lists and texture objects, the name space for program objects may be shared across a set of contexts, as long as the server sides of the contexts share the same address space. If the name space is shared across contexts, any attached objects and the data associated with those attached objects are shared as well.

Applications are responsible for providing the synchronization across API calls when objects are accessed from different execution threads.

## Errors

`GL_INVALID_VALUE` is generated if `program` is neither 0 nor a value generated by OpenGL.

`GL_INVALID_OPERATION` is generated if `program` is not a program object.

`GL_INVALID_OPERATION` is generated if `program` could not be made part of current state.

`GL_INVALID_OPERATION` is generated if `glUseProgram` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGet with the argument `GL_CURRENT_PROGRAM`

glGetActiveAttrib with a valid program object and the index of an active attribute variable

glGetActiveUniform with a valid program object and the index of an active uniform variable

glGetAttachedShaders with a valid program object

glGetAttribLocation with a valid program object and the name of an attribute variable

glGetProgram with a valid program object and the parameter to be queried

glGetProgramInfoLog with a valid program object

glGetUniform with a valid program object and the location of a uniform variable

glGetUniformLocation with a valid program object and the name of a uniform variable

glIsProgram

## See Also

gllAttachShader, glBindAttribLocation, glCompileShader, glCreateProgram, glDeleteProgram, glDetachShader, glLinkProgram, glUniform, glValidateProgram, glVertexAttrib

## Copyright

Copyright 2003-2005 3Dlabs Inc. Ltd. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.