Add display property to control video region

[Nathan Hallquist]

In ticked #2077 Antoine suggested that an X window property to specify the video encoding region could be added.

Initially, I thought I could use dbus and not open this ticket, but I found that dbus does not work right with ssh -Y (or with vglconnect), whereas X window properties work great.

I would, therefore, very much like to be able to do this using x window properties:

xpra control :250 video-region-detection $N false
xpra control :250 video-region-enabled $N true
xpra control :250 reset-video-region $N 
xpra control :250 video-region $N 3 29 1320 950

[Antoine Martin]

Initially, I thought I could use dbus and not open this ticket, but I found that dbus does not work right with ssh -Y (or with vglconnect), whereas X window properties work great.

The xpra server will spawn its own dbus server, you need to find its address before you can talk to it:
ie: you can run this from within the xpra session:

env | grep DBUS
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-rOlSzG0tlW,guid=f214c4b8a5ba96be152814135c2dd605

Or this from any terminal:

xpra info | grep -i env.DBUS

Then you can use it:

$ DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-rOlSzG0tlW,guid=f214c4b8a5ba96be152814135c2dd605 dbus-monitor 

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If this feature is still needed, I would rather have a single window property to control everything, it could be named _XPRA_VIDEO_REGION.
When set, it would be used and video region detection would be turned off.
Simply removing the window property would revert to the default behaviour.
(if really needed, we could support a [0, 0, 0, 0] region to turn off video region)