6.10.1 Prototype Gamut Compression Procedure

The gamut compression callback interface must adhere to the following:

typedef Status (*XcmsCompressionProc)(ccc, colors_in_out, ncolors, index, compression_flags_return)
      XcmsCCC ccc;
      XcmsColor colors_in_out[];
      unsigned int ncolors;
      unsigned int index;
      Bool compression_flags_return[];

ccc	Specifies the CCC.
colors_in_out	Specifies an array of color specifications. Pixel members should be ignored and must remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color specification array.
index	Specifies the index into the array of XcmsColor structures for the encountered color specification that lies outside the screen's color gamut. Valid values are 0 (for the first element) to ncolors - 1.
compression_flags_return	Returns an array of Boolean values for indicating compression status. If a non-NULL pointer is supplied and a color at a given index is compressed, then True should be stored at the corresponding index in this array; otherwise, the array should not be modified.

When implementing a gamut compression procedure, consider the following rules and assumptions:

The gamut compression procedure can attempt to compress one or multiple specifications at a time.
When called, elements 0 to index - 1 in the color specification array can be assumed to fall within the screen's color gamut. In addition, these color specifications are already in some device-dependent format (typically XcmsRGBi). If any modifications are made to these color specifications, they must be in their initial device-dependent format upon return.
When called, the element in the color specification array specified by the index argument contains the color specification outside the screen's color gamut encountered by the calling routine. In addition, this color specification can be assumed to be in XcmsCIEXYZ. Upon return, this color specification must be in XcmsCIEXYZ.
When called, elements from index to ncolors - 1 in the color specification array may or may not fall within the screen's color gamut. In addition, these color specifications can be assumed to be in XcmsCIEXYZ. If any modifications are made to these color specifications, they must be in XcmsCIEXYZ upon return.
The color specifications passed to the gamut compression procedure have already been adjusted to the Screen White Point. This means that at this point the color specification's white point is the Screen White Point.
If the gamut compression procedure uses a device-independent color space not initially accessible for use in the color management system, use XcmsAddColorSpace() to insure that it is added.

Next: Supplied Gamut Compression Procedures

Christophe Tronche, ch@tronche.com