[RFC wayland-protocols] Color management protocol

[Richard Hughes]

On 21 December 2016 at 09:14, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> I suggest that compositors use the CMS you have spent so much time and
> effort perfecting, and you start with the assumption that they will not
> or cannot do so. Why?

I think lcms2 is fine to use; it's widely used in other projects,
tested, and already optionally used in weston.

> Are you implying that the CMS you worked on so hard is impossible to use
> from a compositor?

I think that's basically correct, argyllcms doesn't have any header
files or shared libraries. When using it to generate color profiles
for things like printers from gnome-color-manager I have to spawn the
binaries themselves (and only in a VT...) and then scrape the output.
https://git.gnome.org/browse/gnome-color-manager/tree/src/gcm-calibrate-argyll.c#n273

> Yes! The CMS needs to provide the API that all compositors could use.

I'm not a great fan of pluggable CMSs, it's a bit like designing a car
that has a requirement that the engine is swappable with another
whilst driving down the motorway. I'm a great fan at pointing people
to http://www.islinuxaboutchoice.com/ when they ask about things like
this.

> so "just set the CLUT" is already an outdated approach

This is another point: We're all talking about the
least-common-denominator approach of setting the RGB 8-bit ramps on
the logic it's the only way to set the white point without the
overhead of a shader lookup. Most modern hardware actually supports
some kind of *matrix* and LUT on the crtc output itself, although
there is no common abstract interface that's provided by libdrm, yet.

Richard.