Setting the Xorg gamma ramps

[Richard Hughes]

Currently in GNOME we set the display calibration state using
XRRSetCrtcGamma. This allows us to do a 2D lookup and correct the
device gamma and optionally change the native display temperature. I'm
wondering how we should be doing this using wayland / weston. I
appreciate we'll be doing the advanced sRGB->native gamut mapping as
some kind of sub-surface, but this device calibration state is
orthogonal to that. Most existing display ICC profiles encode a
calibration RGB gamma ramp in them (the 'vcgt' tag) and the profile is
not valid unless the device matches the calibration state.

Ideas welcome, thanks.

Richard