As part of my GSoC project I have to work out a spec that covers how applications should communicate color management related properties between each other and the compositing manager. The main idea of the project is to let the compositing manager do the color management on behalf of the applications. But before that can happen, the applications have to tell the compositing manager how they want to have their colors managed. The following spec I came up with should cover exactly that communication.
How colors should be interpreted is defined in so called 'ICC Profiles', that is a blob that contains all the necessary informations how colors should be interpreted. These profiles are attached to windows so that the compositing manager can get them and do the necessary color conversion. To allow for fine-grained color management (if an application has only a region that it wants to have color managed), the applications have to be able to specify subregions of their window and attach profiles to that. Since toolkits (at least GTK+) already make heavy use of subwindows, using those makes sense to me. So I came up with a document (in the attachment) that describes which window properties and messages are used. Dennis Kasprzyk (compiz developer) wasn't happy that I want to attach properties to subwindows, instead he suggested to attach a list to the top-level window containing tuples of [(sub)window XID / Profile]. But I'd like to keep the properties on the subwindows, I think that will make it easier for toolkits. In GTK+ for example, widgets that create their own subwindow will be able to do the color management completely independent of the other widgets. If all profiles are kept in the top-level window then the widgets first have to find the top-level window and then coordinate with other widgets how to create the list. I'd like to hear other opinions on that. thanks tom
Color Management Spec ----------------------- Overview: Each window can have a color profile attached. This profile is used by the compositing manager to perform automatic colorspace tranformations. _NET_COLOR_PROFILE window property This property specifies the profile. The only type currently supported is 'ICC', it specifies that the data is an ICC profile. Other profile types may be added at a later time. Profiles are inherited from the parent window. Applications can disable the automatic colorspace transformation by setting the profile to None. _NET_COLOR_MANAGER client message By sending this client message to the compositing manager, the application requests that the compositing manager checks whether it can perform the needed colorspace transformations. Upon recieving this client message, the compositing manager traverses the subwindows of the application and saves the attached profiles. It then checks whether it can perform the requested colorspace transformation and sends a reply to the application. The reply is either positive or negative. Upon a positive reply the application can expect that the colors will be automatically corrected by the compositing manager. A negative reply contains a list of all the windows on which the compositing manager can't perform the colorspace transformation. Usually due to the lack of the needed color management module.
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