glutLayerGet (3) - Linux Man Pages
glutLayerGet: Allows you to get some overlay state/option variables.
NAMEglutLayerGet - Allows you to get some overlay state/option variables.
LIBRARYOpenGLUT - overlays
SYNOPSISIn openglut.h Ft int Fn glutLayerGet GLenum eWhat
Returns some useful information about layers.
Or, it would be useful if layers were implemented...
0 unless the window system has told us that the normal layer is damaged (glutPostRedisplay() does not affect this).