Parameters

Description

glLinkProgram links the program object specified by program. A shader object of type GL_VERTEX_SHADER attached to program is used to create an executable that will run on the programmable vertex processor. A shader object of type GL_FRAGMENT_SHADER attached to program is used to create an executable that will run on the programmable fragment processor.

The status of the link operation will be stored as part of the program object's state. This value will be set to GL_TRUE if the program object was linked without errors and is ready for use, and GL_FALSE otherwise. It can be queried by calling glGetProgramiv with arguments program and GL_LINK_STATUS.

As a result of a successful link operation, all active user-defined uniform variables belonging to program will be initialized to 0, and each of the program object's active uniform variables will be assigned a location that can be queried by calling glGetUniformLocation. Also, any active user-defined attribute variables that have not been bound to a generic vertex attribute index will be bound to one at this time.

Linking of a program object can fail for a number of reasons as specified in the OpenGL ES Shading Language Specification. The following lists some of the conditions that will cause a link error.

When a program object has been successfully linked, the program object can be made part of current state by calling glUseProgram. Whether or not the link operation was successful, the program object's information log will be overwritten. The information log can be retrieved by calling glGetProgramInfoLog.

glLinkProgram will also install the generated executables as part of the current rendering state if the link operation was successful and the specified program object is already currently in use as a result of a previous call to glUseProgram. 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.

The program object's information log is updated and the program is generated at the time of the link operation. After the link operation, applications are free to modify attached shader objects, compile attached shader objects, detach shader objects, delete shader objects, and attach additional shader objects. None of these operations affects the information log or the program that is part of the program object.

Notes

If the link operation is unsuccessful, any information about a previous link operation on program is lost (i.e., a failed link does not restore the old state of program). Certain information can still be retrieved from program even after an unsuccessful link operation. See for instance glGetActiveAttrib and glGetActiveUniform.

Errors

GL_INVALID_VALUE is generated if program is not a value generated by OpenGL.

GL_INVALID_OPERATION is generated if program is not a program object.

Associated Gets

glGet with the argument GL_CURRENT_PROGRAM

glGetActiveAttrib with argument program and the index of an active attribute variable

glGetActiveUniform with argument program and the index of an active uniform variable

glGetAttachedShaders with argument program

glGetAttribLocation with argument program and an attribute variable name

glGetProgramiv with arguments program and GL_LINK_STATUS

glGetProgramInfoLog with argument program

glGetUniform with argument program and a uniform variable location

glGetUniformLocation with argument program and a uniform variable name

glIsProgram

Examples

GLuint vshader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vshader, 1, &vertex_shader_source, NULL); // vertex_shader_source is a GLchar* containing glsl shader source code
glCompileShader(vshader);

GLint vertex_compiled;
glGetShaderiv(vshader, GL_COMPILE_STATUS, &vertex_compiled);
if (vertex_compiled != GL_TRUE)
{
    GLsizei log_length = 0;
    GLchar message[1024];
    glGetShaderInfoLog(vshader, 1024, &log_length, message);
    // Write the error to a log
}

GLuint fshader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fshader, 1, &fragment_shader_source, NULL); // fragment_shader_source is a GLchar* containing glsl shader source code
glCompileShader(fshader);

GLint fragment_compiled;
glGetShaderiv(fshader, GL_COMPILE_STATUS, &fragment_compiled);
if (fragment_compiled != GL_TRUE)
{
    GLsizei log_length = 0;
    GLchar message[1024];
    glGetShaderInfoLog(fshader, 1024, &log_length, message);
    // Write the error to a log
}

GLuint program = glCreateProgram();

// This step is unnecessary if you use the location specifier in your shader
// e.g. layout (location = 0) in vec3 position;
glBindAttribLocation(program, 0, "position"); // The index passed into glBindAttribLocation is
glBindAttribLocation(program, 1, "texcoord"); // used by glEnableVertexAttribArray. "position"
glBindAttribLocation(program, 2, "normal");   // "texcoord" "normal" and "color" are the names of the
glBindAttribLocation(program, 3, "color");    // respective inputs in your fragment shader.

glAttachShader(program, vshader);
glAttachShader(program, fshader);
glLinkProgram(program);

GLint program_linked;
glGetProgramiv(program, GL_LINK_STATUS, &program_linked);
if (program_linked != GL_TRUE)
{
    GLsizei log_length = 0;
    GLchar message[1024];
    glGetProgramInfoLog(program, 1024, &log_length, message);
    // Write the error to a log
}

Tutorials

open.gl - Geometry Shaders
open.gl - The Graphics Pipeline
open.gl - Transform Feedback
opengl-tutorial.org - Tutorial 2 : The first triangle

See Also

glAttachShader, glBindAttribLocation, glCompileShader, glShaderBinary, glCreateProgram, glDeleteProgram, glDetachShader, glUniform, glUseProgram, glValidateProgram