This command can be used if backface culling should not be performed. If the boolean flag is true backfacing polygons are "inverted" (their surface normal is negated) and then rendered. This is useful if an object description does not use a consequent ordering of the vertices. This also controls hidden line elimination when doing line rendering. The rendering step can be slowed down considerably since, on the average, twice as many polygons need to be rendered. The default is that backface culling should be performed (false). If flag is not specified, the current value is returned.