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glBindFragDataLocation

Name

glBindFragDataLocation — bind a user-defined varying out variable to a fragment shader color number

C Specification

void glBindFragDataLocation(GLuint program,
GLuint colorNumber,
const char * name);

Parameters

program

The name of the program containing varying out variable whose binding to modify

colorNumber

The color number to bind the user-defined varying out variable to

name

The name of the user-defined varying out variable whose binding to modify

Description

glBindFragDataLocation explicitly specifies the binding of the user-defined varying out variable name to fragment shader color number colorNumber for program program. If name was bound previously, its assigned binding is replaced with colorNumber. name must be a null-terminated string. colorNumber must be less than GL_MAX_DRAW_BUFFERS.

The bindings specified by glBindFragDataLocation have no effect until program is next linked. Bindings may be specified at any time after program has been created. Specifically, they may be specified before shader objects are attached to the program. Therefore, any name may be specified in name, including a name that is never used as a varying out variable in any fragment shader object. Names beginning with gl_ are reserved by the GL.

In addition to the errors generated by glBindFragDataLocation, the program program will fail to link if:

  • The number of active outputs is greater than the value GL_MAX_DRAW_BUFFERS.

  • More than one varying out variable is bound to the same color number.

Notes

Varying out varyings may have indexed locations assigned explicitly in the shader text using a location layout qualifier. If a shader statically assigns a location to a varying out variable in the shader text, that location is used and any location assigned with glBindFragDataLocation is ignored.

Errors

GL_INVALID_VALUE is generated if colorNumber is greater than or equal to GL_MAX_DRAW_BUFFERS.

GL_INVALID_OPERATION is generated if name starts with the reserved gl_ prefix.

GL_INVALID_OPERATION is generated if program is not the name of a program object.

Associated Gets

glGetFragDataLocation with a valid program object and the the name of a user-defined varying out variable

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

glCreateProgram, glGetFragDataLocation

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