HDR support in Wayland/Weston

[Michel Dänzer]

On 2019-03-08 9:41 a.m., Graeme Gill wrote:
> Michel Dänzer wrote:
> 
>> It was never reliable for that. Other clients using any of those
>> mechanisms could always interfere, at least for the RandR compatibility
>> output.
> 
> I disagree. It was reliable in the sense that running the
> profile loader set it to a known state, irrespective
> of whatever other applications may have done via
> other API's.

You're assuming that the mechanism used by the profile loader directly
clobbers the HW LUT, making any adjustments made via other mechanisms
ineffective[0]. Even so, other clients can make adjustments using the
other mechanisms (or even the same one) at any time, which would again
clobber the HW LUT, interfering with the profile. Not reliable.

[0] This results in bug reports like
https://bugs.freedesktop.org/27222

> With the behavior changed to combine all the API settings, there is no
> simple way to set it to a known state.

You can set all other mechanisms to pass-through. If you want to be nice
to your users, maybe save their previous states and restore them
afterwards. Of course, if you want to prevent other clients from
interfering, you'd probably need to grab the server (which might result
in the desktop freezing with a compositing manager).


-- 
Earthling Michel Dänzer               |              https://www.amd.com
Libre software enthusiast             |             Mesa and X developer