[RFC wayland-protocols] Color management protocol

[Pekka Paalanen]

On Wed, 21 Dec 2016 11:38:41 +0200
Pekka Paalanen <ppaalanen at gmail.com> wrote:

> On Wed, 21 Dec 2016 11:08:06 +1100
> Graeme Gill <graeme2 at argyllcms.com> wrote:
> 
> > Richard Hughes wrote:  
> > > Anything more and the application author will just
> > > decide it's not worth the bother. To calibrate we just ask for a
> > > surface that's not going to be tampered with, but we don't want to
> > > optimize for this super-uncommon case.    
> > 
> > I disagree - leave it to be an afterthought, and it will be
> > done badly or left out completely, crippling the practicality
> > of color management for the system.  
> 
> Designing that is trivial:
> 
> GLOBAL cms_calibrator
> - request: create_calibration_surface(wl_surface, new cms_calibration_surface)
> 	# Assigns wl_surface role.
> 
> INTERFACE cms_calibration_surface
> 	# Surfaces with this role will only be shown on the set output,
> 	# with direct color path bypassing all color-management, and
> 	# and the hardware has been reset to neutral/identity settings.
> 	# (or whatever requirements are appropriate, you can decide
> 	# what to write here)
> - request: set_output(wl_output)
> 	# Which output this surface targets. The compositor replies
> 	with a
> 	# configure event.
> - event: configure(width, height)
> 	# delivers the width and height the application needs to use
> 
> 
> How it operates from a client perspective:
> 
> 1. create a wl_surface
> 2. bind to cms_calibrator
> 3. send create_calibration_surface
> 4. send set_output
> 5. wait for configure
> 6. draw the calibration surface in the correct size
> 7. use Presentation feedback interface to ensure the calibration
>    surface is show with the latest content
> 8. do what you want to do with the colorimeter
> 9. go to 6 to update the image if necessary
> 10. destroy cms_calibration_surface and wl_surface; the display
>     automatically returns to normal
> 
> 
> To be user friendly, one probably wants to add an event in case the
> user denies the request to show the calibration window as it will have
> temporary global effects.
> 
> Whether the global needs to be privileged or not, and how privileges
> are implemented are an orthogonal matter.

Hi Niels,

I really should have CC'd you on this one.

I also forgot to mention that surfaces with the cms_calibration_surface
role, when actually presented, would also guarantee that nothing else
will be shown on that specific output, screen saving will not activate,
etc. anything that might hamper calibration will not happen.

You'd also want an event telling that the user has interrupted the
showing of the calibration window, so that the calibration app cannot
hog the output indefinitely even if it freezes. That might be the same
event telling the user denied it in the first place.

This is something you cannot achieve with just a pass-through color
profile.


Thanks,
pq
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