[cairo] cmyk support in Inkscape/Cairo

[Ian Britten]

Carl Worth wrote:

>> Which cmyk features are needed and currently not implemented?
> 
> For cairo, it's really a matter of users with actual needs telling us
> what they need, (that could be inkscape developers, for example). And
> then, together, we'll try to come up with the most "cairo-like" way of
> exposing the functionality.

For my users, I don't see a path that lets me use Cairo for our CMYK
needs, and I suspect I'll have to maintain my own PS code for this
(Primarily because of the RGB interfaces Cairo uses).  However, I
haven't investigated this yet, and am just adding my $0.02 at this
time  :)

In some workflows, my users will *define* their colours in CMYK (ie In
their own palette).  When they produce PS, they want those *exact*
colours written out, not the result of a CMYK -> RGB -> CMYK conversion.
As such, we maintain an abstract 'colour' class, with derived 'rgb',
'cmyk', etc, variants, which maintain the defined colours as they were
originally specified.

When the data is drawn to the screen, it goes through a CMYK -> RGB
conversion (Since most graphics toolkits only work with RGB), and this
is considered ok, since it's "only on-screen".  However, when they
print, they get their exact CMYK colours in their PS output, as
required.

Ian