I will try to test this myself this week.
I have concerns about connecting graphics in VirtualBox with the host system.
Docker Toolbox uses seperate virtual system (based on Linux) so maybe graphics will be forwarded only to it not to Windows.
But if graphics can be forwarded directly to Windows, it will probably work.
I will post the solution when I find it.
You're right, this could be a problem with forwarding stopping at the virtual system.
I am curious what your results will be!
I tested this and it works!
Display variable should be set to address of host (Windows) computer.
When using boot2docker image, new VirtualBox Host-Only Network will be created. In it, host computer will probably have address 192.168.99.1, so DISPLAY should be set to 192.168.99.1:0.0
VirtualBox Host-Only Network
If that won't work, new bridged network can be added to boot2docker image and DISPLAY should be set to local address of host.
Also, because boot2docker image has very low RAM and GPU memory, GUI apps will often crash. This could probably be fixed with higher RAM and GPU memory settings in VirtualBox.
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