OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Uniform Blocks

As your shader programs become more complex, it’s likely that the number of uniform variables they use will increase. Often the same uniform value is used within several shader programs. As uniform locations are generated when a shader is linked (i.e., when glLinkProgram() is called), the indices may change, even though (to you) the values of the uniform variables are identical. Uniform buffer objects provide a method to optimize both accessing uniform variables and enabling sharing of uniform values across shader programs.

As you might imagine, that given uniform variables can exist both in your application and in a shader, you’ll need to both modify your shaders and use OpenGL routines to set up uniform buffer objects.