glGetActiveSubroutineName

glGetActiveSubroutineName: man4/glGetActiveSubroutineName.xml

glGetActiveSubroutineName queries the name of an active shader subroutine uniform from the program object given in program. index specifies the index of the shader subroutine uniform within the shader stage given by stage, and must between zero and the value of GL_ACTIVE_SUBROUTINES minus one for the shader stage. The name of the selected subroutine is returned as a null-terminated string in name. The actual number of characters written into name, not including the null-terminator, is is returned in length. If length is null, no length is returned. The maximum number of characters that may be written into name, including the null-terminator, is given in bufsize.