Overriding target screen for attach

[Peter Gervai]

[As per IRC] it would be useful to be able to override the target screen of the windows "attach" physically display. You said that xpra tries to preserve the screen the window was last attached on, which is not always desirable.

The context is moving windows between separate screens (eg. from :0.0 to :0.1).

[Antoine Martin]

First thing to fix is to honour the actual screen if one is specified:

DISPLAY=:0.1 xpra attach ..

Should not end up showing any windows on :0.0, even if they were shown there previously. (ideally detecting the screen vs display without parsing the $DISPLAY string)

[Peter Gervai]

Related to #1369 which touches the other side of moving windows between physical monitors / screens / displays.

[Peter Gervai]

To detail a bit more what I have on mind:

xpra control :666 setoption window.1.target ':0.0'

or

xpra retarget :666 window.3 ':0.1'
xpra retarget :666 window.4 ':1'

or similar.

[Antoine Martin]

Fixes (lots of small things) and updates:

• r17818: env var to override current behaviour, ie: XPRA_HONOUR_SCREEN_MAPPING=0 xpra attach ... to disable setting the screen the window will appear on
• r17820: control command to set the screen the window will be shown on for a particular user, syntax: client-property WINDOW-ID UUID property-name value [type], ie: xpra control :10 client-property 1 9a6b367ff56bd8348424399fdd975d95d633e822 screen 0 int, you can find your uuid by running: python xpra/os_util.py or with "xpra info" after connecting.
• r17821: default to not setting the screen if the $DISPLAY has one already (ie: :20.1)

@grin: does that work for you?