A solution for gamma-adjustment support in Wayland

[Graeme Gill]

Hi,

Daniel Stone wrote:
> 'The size and depth' and 'the CLUT' are no longer applicable. Colour
> management units, incorporating two LUTs and a matrix (coarsely,
> degamma-transform-regamma) are becoming rather common now. These units
> can be present per-plane as well as per-output/pipe. Sometimes you
> have to make tradeoffs.

Just because some hardware is a lot more capable, is no reason to ignore
supporting currently expected functionality.

Simple per channel hardware lookup tables have been supported
by graphics card software for a very long time (Our X terminals
in the late 80's certainly had them), so this level of
support can be assumed as almost universal, and there are
well understood reasons for using such hardware to set
the state of the display for color management purposes at
least (which I have articulated elsewhere). Usage of further
HW capabilities (matrices etc.) are much less clear - no
application interested in fully utilizing a displays best
possible gamut has any use for them (since they can only
reduce the gamut), and there is much more flexibility in
dealing with non color managed applications in the applications
and/or compositor, so that they can co-exist with full color aware
applications.

> The point is that I'm extremely wary of copying X11 by way of encoding
> this into an API; it's a truly dizzying space to even enumerate, let
> alone abstract.

I'm not sure what you are thinking of here - the existing per channel
VideoLUT API's are universally simple, and the only temptation in
making changes to this might be in the direction of better coordinating
competing use of this shared resource.

I agree that expanding such API's to encompass more advanced HW capabilities is
something of a project, and might not even be a good direction to proceed
if other alternatives are a more enticing use of time and effort (installable
shaders in the rendering pipeline ??)

Regards,

Graeme Gill.