[cairo] Subtractive API, part 1

[ecir hana]

Just to check if I understood....

There is no need of using ICC profile for spot color, as long as I
could define LAB fallback, right? And if we assumed CIE LAB D50
(because of ICC?), like:

void cairo_set_source_spot(cairo_t *cr, const char *name, double l,
double a, double b);

would this be so far the best variant?

Then, I asked what to do if I don't know the LAB values for a certain
spot color. In such case there could be a helper function which would
return LAB for given profile and tints:

lab_t get_lab(cairo_profile_t *profile, ...);
where "..." are the colorant intensities / tints.

For example:
c = get_lab(PROFILE_SWOP, 0.1, 0.2, 0.3, 0.4);
cairo_set_source_spot("MyColor", c.l, c.a., c.b);

?