SpecIccForCairo

Why

In order for inkscape to produce CMYK PDFs and PSs with cairo, Cairo needs to support ICC. This is an intent to propose a Cairo API that would be suitable with inkscape needs.

Profiles

A set of profiles will apply to the whole Cairo surface. Cairo needs to be able to compute a transform from this set. We can get inspiration from the lcms api [1], in particular the cmsCreateMultiprofileTransform (more generic than cmsCreateTransform that handles only a pair of color profiles).

So a proposal would be:

typedef enum cairo_color_intent {
  CAIRO_COLOR_INTENT_PERCEPTUAL,
  CAIRO_COLOR_INTENT_RELATIVE_COLORIMETRIC,
  CAIRO_COLOR_INTENT_SATURATION,
  CAIRO_COLOR_INTENT_ABSOLUTE_COLORIMETRIC
} cairo_color_intent_t;

typedef struct cairo_color_profile cairo_color_profile_t;

void cairo_pattern_add_profile_pair (cairo_pattern_t *pat, 
                                     cairo_color_profile_t *in, 
                                     cairo_color_profile_t *out);

void cairo_pattern_remove_profiles (cairo_pattern_t *pat);

void cairo_pattern_set_color_intent(cairo_pattern_t *pat,
                                    cairo_color_intent_t intent);

Colors

All the functions handling colors, like cairo_set_source_rgba and cairo_set_source_rgb, must be complemented (or replaced) with

void cairo_set_source_profiled_color  (cairo_t *cr, void* color);

format of the color is the one defined by DWORD input_format.