glBindFragDataLocationIndexed - bind a user-defined varying out variable to a fragment shader color number and index
void glBindFragDataLocationIndexed(GLuint program, GLuint colorNumber, GLuint index, const char *name);
glBindFragDataLocationIndexed specifies that the varying out variable name in program should be bound to fragment color colorNumber when the program is next linked. index may be zero or one to specify that the color be used as either the first or second color input to the blend equation, respectively.
The bindings specified by glBindFragDataLocationIndexed 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.
If name was bound previously, its assigned binding is replaced with colorNumber and index. name must be a null-terminated string. index must be less than or equal to one, and colorNumber must be less than the value of GL_MAX_DRAW_BUFFERS if index is zero, and less than the value of GL_MAX_DUAL_SOURCE_DRAW_BUFFERS if index is greater than or equal to one.
In addition to the errors generated by glBindFragDataLocationIndexed, the program program will fail to link if:
Varying out varyings may have 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.
GL_INVALID_VALUE is generated if colorNumber is greater than or equal to GL_MAX_DRAW_BUFFERS.
GL_INVALID_VALUE is generated if colorNumber is greater than or equal to GL_MAX_DUAL_SOURCE_DRAW_BUFERS and index is greater than or equal to one.
GL_INVALID_VALUE is generated if index is greater than one.
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.
glGetFragDataLocation() with a valid program object and the the name of a user-defined varying out variable
glGetFragDataIndex() with a valid program object and the the name of a user-defined varying out variable
glCreateProgram(), glLinkProgram() glGetFragDataLocation(), glGetFragDataIndex() glBindFragDataLocation()
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