single logical screen EDID proposal

Kai-Uwe Behrmann ku.b at
Wed Apr 19 00:29:17 PDT 2006

EDID information describing inbuild display capabilities is stored 
into one property in the root window of a X server.

Single logical screen configurations with a unified root window across 
all screens have just one root window to store such information for all 
physical screens. Currently no EDID is stored in that root window at all 
(tested with Xorg-6.8 and twinview style nvidia configuration).

To let client side application access these valuable data, my proposal 
suggests to use following behaviour

1. XFree86_DDC_EDID1_RAWDATA root property is created for the 0 (first)
   screen. This is as is today.

2. XFree86_DDC_EDID1_RAWDATA_[1-9] properties follow up for each 
   additional screen inside a single logical screen configuration. 

The numbering in point 2 should follow the screen numbering.

The advantage is the current behaviour remains for single physical 
screen configurations and multi screen configurations with one root 
window per physical screen.
For single logical screen configurations the same information set would 
then become available through the proposed additional properties.

I followed the nomenclatura found in a older user manual.
Even though termes used are a bit confusing like "screen" <-> "xinerama 
screen" or physical versus logical. But this is possibly due to the 
current transition to a Xinerama alike behaviour.

Kai-Uwe Behrmann
                                + development for color management 
                                + imaging / panoramas
                                + email: ku.b at

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