To switch off colour matching for all drawing surfaces.
SUBROUTINE USE_APPROXIMATE_COLOURS@( BOOL )
By default, routines that draw to a drawing surface use a colour matching algorithm that selects an optimum colour match corresponding to the supplied colour value. Colour matching can be switched off (for all drawing surfaces) by calling this routine with the argument set to zero. A non-zero value switches on again.
If automatic colour matching is switched off, a matched colour can still be obtained from GET_MATCHED_COLOUR@. The result is used as an RGB value in any of the drawing surface routines.
Using this routine may lead to a significant improvement in the performance of your program since colour matching is often unnecessary. When colour matching is desirable, it is only necessary to apply the matching algorithm once for each colour that is used.
This function is not needed on modern 24-bit displays.