[Openicc] net-color spec 0.2 DRAFT 1

[Kai-Uwe Behrmann]

Hello,

the net-color spec [1] is now ready for revision. It pretty much reflects 
what is currently supported in Oyranos' colour_desktop plugin for compiz.

The net-color spec relies implicitely on the ICC Profile in X spec.

Find the draft attached for convenient reading.



kind regards
Kai-Uwe Behrmann
-- 
developing for colour management 
www.behrmann.name + www.oyranos.org

[1] http://www.oyranos.org/scm?p=xcolor.git;a=blob;f=docs/net-color-spec;h=a8d46ab8d66a1ecf6776b26af0695d5aeefd3292;hb=master
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    net-color spec 0.2
   ====================

DRAFT 1

   Revision History
  ------------------
Revision 0.1            2008-07-21  Tomas Carnecky
                                      initial incomplete spec for 
                                      Color Management near X
Draft for Revision 0.2  2010-05-16  Kai-Uwe Behrmann
                                      clearify XcolorRegion, add references,
                                      history, date and headers,
                                      remove XRandR, _NET_COLOR_MANAGEMENT and
                                      _NET_COLOR_PROFILES from this version,
                                      add _NET_COLOR_REGIONS and
                                      _NET_COLOR_DESKTOP

   Introduction
  --------------

The net-color spec defines a protocol which can be used by X11 clients to
offload color correction and transformation into the compositing manager. The
basic idea is to communicate client side regions to the X11 server.
The regions can of this version have no ICC profile attached, which means
a color server, typical in a compositing manager, shall not color manage 
these regions. These regions then are in the responsibility of the application.


   Color Region
  --------------

A color region is described by the following C structure:

typedef struct {
        uint32_t region;  /* window centric XserverRegion               */
        uint8_t md5[16];  /* ICC MD5 hash of the associated ICC profile */
} XcolorRegion;


It defines a region and the attached color profile. Color regions are attached
to windows and used by the compositing manager to apply the proper color
transformation. Windows can have an unlimited amount of regions attached, though
only the first 2 * 2^32 can be referenced.
As of this spec the md5 shall be set to zero to signal the region is already
color managed by the application.

   Atoms
  -------

 _NET_COLOR_REGIONS:

The atom is attached to windows and lists the XcolorRegion's defined for that
specific window. The application is responsible to update the contained 
informations, e.g. on region resize or move inside the window.
The type is XA_CARDINAL and values are stored in network byte order.

 _NET_COLOR_TARGET:

Is attached to windows and specifies on which output the window should
look correctly. The type is XA_STRING.

 _NET_COLOR_DESKTOP:

The atom is attached on the root window to tell about a color servers activity.
The content is of type XA_STRING and has four sections separated by a 
empty space char ' '. 
The _NET_COLOR_DESKTOP atom is a string with following usages:
- uniquely identify the colour server
- tell the name of the colour server
- tell the colour server is alive
All sections are separated by one space char ' ' for easy parsing.

The first section contains the process id (pid_t) of the color server process, 
which has set the atom.
The second section contains time since epoch GMT as returned by time(NULL).
The thired section contains the bar '|' separated and surrounded
capabilities:
  - NCP  _NET_COLOR_PROFILES
  - NCT  _NET_COLOR_TARGET
  - NCM  _NET_COLOR_MANAGEMENT
  - NCR  _NET_COLOR_REGIONS
  - V0.3 indicates version compliance to the _ICC_Profile in X spec
The fourth section contains the servers name identifier.

As of this specification the third section must contain NCR and the 
supported _ICC_PROFILE in X version. NCT is optional.

A example of a valid atom might look like:
_NET_COLOR_DESKTOP(STRING) = "4518 1274001512 |NCR|V0.3| compiz_colour_desktop"

   References
  ------------

1. X window system (hhtp://www.x.org)
2. International Color Consortium (http://www.color.org)
3. _ICC_Profile in X (http://www.freedesktop.org/wiki/Specifications/icc_profiles_in_x_spec)
4. Xcolor reference implementation (git clone git://www.oyranos.org/git/xcolor)
5. colour_deskop colour server for compiz (git clone git://www.oyranos.org/git/oyranos)
6. xcmsevents monitor tool (git clone git://www.oyranos.org/git/oyranos)


   Todo
  ------

The relation to the _ICC_Profile in X spec is undefined in that a monitor 
profile as provided by the _ICC_PROFILE(_xxx) atom is for unaware applications
not correct during the run of the color server. Necessarily a double color
conversion will happen for net-color spec unaware applications, which is a 
clear conflict. A _ICC_DEVICE_PROFILE(_xxx) atom during color server run is 
in discussion.


2008 (c) Tomas Carnecky, 2010 (c) Kai-Uwe Behrmann