XcmsCompressionProc XcmsSetCompressionProc(ccc, compression_proc, client_data)
      XcmsCCC ccc;
      XcmsCompressionProc compression_proc;
      XPointer client_data;
| ccc | Specifies the CCC. | 
| compression_proc | Specifies the gamut compression procedure that is to be applied when a color lies outside the screen's color gamut. If NULL is specified and a function using this CCC must convert a color specification to a device-dependent format and encounters a color that lies outside the screen's color gamut, that function will return XcmsFailure . | 
| client_data | Specifies client data for the gamut compression procedure or NULL. |