[cairo] Spot colors (and CMYK)

[Bill Spitzak]

Francois Robert wrote:
> Bill Spitzak wrote :
>> For spot colors the spot color is recovered by looking up the sRGB color. 
>> This assumes a 1:1 mapping >between spot color and sRGB. Another channel is 
>> used to transfer this information.
> 
> Actually, a spot color (or rather a 'colorant' or an 'ink') is identitified by a human-readable name. The proposed structure may be fine for rendering a spot color(ant) on an RGB device. On a PS or a PDF device, the name must be passed (along with alternate colorspace etc...) So the definition details of a spot color that aims to be passed-through to a PS or a PDF backend unfortunately requires more than just some RGB equivalent. (but being unfamilliar with the code, that may be stored elsewhere already ?)

I think I didn't explain what I had in mind correctly.

What I proposed is that the front end uses the spot color to index some 
table of rgb values. All spot colors have different rgb values. The back 
end has an inverse table that translates a given rgb value back to the 
spot color.

The enumeration is still needed so that the fact that it is a spot color 
and not just an rgb triple is preserved.

The rgb values probably resemble the spot color but that is not 
necessary for this to work.