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xvfb: Add multiple crtc support

Andy Myers requested to merge andy-zetier/xserver:multiple_vfb_crtcs into master

Multiple CRTCs can be added on a per-screen basis with the new -crtcs option. Each CRTC has one associated output. Outputs beyond the first are disconnected by default and can be connected by setting a mode. Outputs can be disconnected by setting the associated CRTC's mode and output to None.

Signed-off-by: Andy Myers andy.myers@zetier.com

These changes allow Xvfb clients to work with multiple virtual displays. For example, running the following with these changes:

export DISPLAY=:5 &&
Xvfb :5 -screen 0 1600x1200x24 -crtcs 3 &
gnome-shell &
sleep 5 && xwd -root > fb.xwd && convert fb.xwd single.png

Yields a single.png of:

single

Modifying the CRTCs/outputs with xrandr like so:

xrandr &&
xrandr --newmode "800x600" 38.25 800 832 912 1024 600 603 607 624 -hsync +vsync &&
xrandr --addmode screen_1 "800x600" &&
xrandr --addmode screen_2 "800x600" &&
xrandr --output screen_1 --mode "800x600" --primary &&
xrandr --output screen_2 --mode "800x600" --pos 800x0 &&
xrandr --output screen --off &&
xrandr &&
xwd -root > fb.xwd && convert fb.xwd double.png

Yields a double.png of:

double

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