bind a user-defined varying out variable to a fragment shader color number
glBindFragDataLocation( GLuint ( program ) , GLuint ( colorNumber ) , const char * ( name ) )-> void
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.
Varying out varyings may have indexed locations assigned explicitly in the shader text using a
locationlayout 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_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
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