HDR support in Wayland/Weston

Graeme Gill graeme2 at argyllcms.com
Thu Mar 7 21:35:20 UTC 2019

Michel Dänzer wrote:

> It sounds like KMS leases could be a pretty good fit for a calibration
> application. It can lease each output individually from the Wayland
> compositor and fully control it using KMS APIs, while the Wayland
> compositor continues running normally on other outputs.

There seems to be this idea that has got a hold amongst many commentators
on this topic here, that somehow the display calibration and profiling
application NEEDs raw and direct access to the a display to operate.

If you have actually sat down and written such an application yourself,
(which I have, and have been maintaining on 3 separate operating systems
for the last 10 years +), then I'm willing to hear your reasons for
thinking that.

If you haven't actually written such an application (or at least
seriously sat down to understand color management and thought through
the implications it has on the functional requirements of such applications),
then let me state again that YOU ARE COMPLETELY MISTAKEN. The reality
is the opposite of what you are thinking. A calibration and profiling
application needs access to the display IN ITS NORMAL OPERATING STATE.
That is the only way it can be certain that it is characterizing its
operating color behavior, and that the calibration machinery is behaving
the same way it does when working with actual applications.

It's only a "special" application in needing to be able to position
a window on a specific screen at a specific location in such a way that
the window is not obscured, and has access to the color management configuration
(setting calibration curves & installing color profiles).
In every other way it is an ordinary application that can regularly run
alongside all the other ordinary applications, and needs access
to all the ordinary application facilities for providing a UI that
the user can use (and access to connected hardware, typically via
USB or Bluetooth).

	Graeme Gill.

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