Pekka Paalanen authored May 28, 2021 and Pekka Paalanen committed Nov 23, 2021

Roughly speaking, a color profile describes the color space of content
or an output. Under the hood, the description includes one or more ways
to map colors between the profile space and some standard profile
connecting space (PCS).

This object is not called a color space. A color space has a unique
definition, while a color profile may contain multiple different
mappings depending on render intent. Some of these mappings may be
subjective, with an artistic touch.

When a source color profile and a destination color profile are combined
under a specific render intent, they produce a color transformation.
Color transformations are already preresented by weston_color_transform.

This patch adds the basic API for color profile objects. Everything
worthwhile of these objects is implemented in the color managers:
color-noop never creates these, and in color-lcms they are basically a
container for cmsHPROFILE, the Little CMS object for color profiles.
Color profile objects will not be interpreted outside of the color
managers, unlike color transformations.

For a start, the color manager API has one function to create color
profiles: from ICC profile data. More creation functions for other
sources will be added later.

The API has errmsg return parameter for error messages. These are not
simply weston_log()'d, because CM&HDR protocol will allow clients to
trigger errors and the protocol handles that gracefully. Therefore
instead of flooding the compositor logs, the error messages will
probably need to be relayed back to clients.

Color-lcms is expected to create a cmsHPROFILE for all kinds of color
profiles, not just for those created from ICC profile data. Hence,
color-lcms will fingerprint color profiles by the MD5 hash which Little
CMS computes for us. The fingerprint is used for de-duplication: instead
of creating copies, reference existing color profiles.

This code is very much based on Sebastian Wick's earlier work on Weston
color management, but structured and named differently.

Co-authored-by: Sebastian Wick <sebastian@sebastianwick.net>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>