glGetUniformIndices

glGetUniformIndices: man3/glGetUniformIndices.xml

glGetUniformIndices retrieves the indices of a number of uniforms within program. program must be the name of a program object for which the command glLinkProgram must have been called in the past, although it is not required that glLinkProgram must have succeeded. The link could have failed because the number of active uniforms exceeded the limit. uniformCount indicates both the number of elements in the array of names uniformNames and the number of indices that may be written to uniformIndices. uniformNames contains a list of uniformCount name strings identifying the uniform names to be queried for indices. For each name string in uniformNames, the index assigned to the active uniform of that name will be written to the corresponding element of uniformIndices. If a string in uniformNames is not the name of an active uniform, the special value GL_INVALID_INDEX will be written to the corresponding element of uniformIndices. If an error occurs, nothing is written to uniformIndices.

glGetUniformIndices is available only if the GL version is 3.1 or greater.