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glGetAttribLocation

Name

glGetAttribLocation — Returns the location of an attribute variable

C Specification

GLint glGetAttribLocation(GLuint  program,
 const GLchar * name);

Parameters

program

Specifies the program object to be queried.

name

Points to a null terminated string containing the name of the attribute variable whose location is to be queried.

Description

glGetAttribLocation queries the previously linked program object specified by program for the attribute variable specified by name and returns the index of the generic vertex attribute that is bound to that attribute variable. If name is a matrix attribute variable, the index of the first column of the matrix is returned. If the named attribute variable is not an active attribute in the specified program object or if name starts with the reserved prefix "gl_", a value of -1 is returned.

The association between an attribute variable name and a generic attribute index can be specified at any time by calling glBindAttribLocation. Attribute bindings do not go into effect until glLinkProgram is called. After a program object has been linked successfully, the index values for attribute variables remain fixed until the next link command occurs. The attribute values can only be queried after a link if the link was successful. glGetAttribLocation returns the binding that actually went into effect the last time glLinkProgram was called for the specified program object. Attribute bindings that have been specified since the last link operation are not returned by glGetAttribLocation.

Errors

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

GL_INVALID_OPERATION is generated if program is not a program object.

GL_INVALID_OPERATION is generated if program has not been successfully linked.

Associated Gets

glGetActiveAttrib with argument program and the index of an active attribute

glIsProgram

Examples

Retrieve uniform data after the shader has been compiled
// The index returned from these GLint functions gets passed to glEnableVertexAttribArray during rendering.
GLint position_attrib_index = glGetAttribLocation(program, "position"); // program is what is returned by glCreateProgram.
GLint texcoord_attrib_index = glGetAttribLocation(program, "texcoord");
GLint normal_attrib_index = glGetAttribLocation(program, "normal");
GLint color_attrib_index = glGetAttribLocation(program, "color");

glBindFragDataLocation(program, 0, "output_color"); // "output_color" is an output value in your vertex shader and an input value in your fragment shader.

GLint num_uniforms;
glGetProgramiv(program, GL_ACTIVE_UNIFORMS, &num_uniforms);
GLchar uniform_name[256];
GLsizei length;
GLint size;
GLenum type;
for (int i = 0; i < num_uniforms; i++)
{
    glGetActiveUniform(program, i, sizeof(uniform_name), &length, &size, &type, uniform_name);
    // ... save this uniform data so it can be used during rendering
}

See Also

glBindAttribLocation, glLinkProgram, glVertexAttrib, glVertexAttribPointer

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