Win10 Quick Assist screen-share shows corrupted desktop

[Jim Avera]

If Windows 10 guest shares its screen with a remote user using the built-in "Quick Assist" utility, the other user sees a corrupted screen. Specifically, everything is slanted at a 45 degree angle (see screenshot). It looks like each horizontal row of pixels is offset slightly from the previous one.

HOST: Ubuntu linux 20.04, X-org, Intel graphics GUEST: Windows 10 64-bit

STEPS TO REPRODUCE: In some other Win10 machine (VM or real):

1. Start the "Quick Assist" app.
2. Click the "Assist another person" button at the bottom (sign in to a microsoft account if prompted) Note the "Security code" number displayed

In the Vbox VM Win10 guest:

3. Start "Quick Assist"
4. Enter the Security code in the "Code from assistant" box

RESULTS: The remote Win10 sees the VM guest's desktop in an unusably skewed form

[Jim Avera]

Screenshot on remote system showing corrupted display

[Jim Avera]

Virtualbox Version 6.1.12 r139181 (Qt5.12.8)

(wasn't offered as an option in the drop-down)

[Jim Avera]

[Revised with specific instructions to repro every time]

Still reproduced using VirtualBox 7.0, either between a VM and bare-metal system or two VMs. It seems to depend on certain screen-size ratios. I suspect (not sure) that the bug occurs when one of the screens has "odd" dimensions, e.g. not divisible by 2.

Here are instructions to repro every time using two VMs running Windows 10. I used the 'xdotool' to set the window sizes, but probably you can do it manually as well.

REPRO WITH TWO VMs on a Linux host:

1. sudo apt install xdotool # if necessary

1. Obtain a Windows 10 VM, called "A" here
2. Make a clone, called "B" here.  I used "Linked Clone" and "Generate new MAC..." options.
    (do not re-use UUIDs or else the VMs can not run simultaneously)

3. Start both Windows VMs.  Put "A" in upper-left corner, "B" in lower-right.
   Then in a terminal:

4. xdotool windowsize $(xwininfo | perl -n -e '/.*Window id: (\S*)/ && print $1') 997 777
   Click in VM "A" to set it's window size

5. xdotool windowsize $(xwininfo | perl -n -e '/.*Window id: (\S*)/ && print $1') 1024 640  
   Click in VM "B" to set it's window size.

6. In both VM's run the "Quick Assist" app (type "Quick" into the Search bar to find it)
    6a. In "B" (the 1024x640 one), click "Help someone", sign in (I used Github), and copy the security code it displays
    6b. In "A" paste the code; click "Submit"; click "Allow" screen sharing

RESULTS: Corrupted screen image in maching "B". See attached screenshot.

The problem does not occur if machine A is an even size like 1000 x 768 instead of 997 x 777. In general the size is set by users and difficult to control.

Suggestion: If there is no easy way to support "odd" dimensions, then make VM windows (on the host) respond to resize events by snapping to the nearest even number of pixels. So for example, when I told "A" to resize to 997 x 777, it would instead become 996 x 776.

This might be a Microsoft bug unrelated to VBox video. I can repro if "A" is the VM with size 997 x 777 and "B" is a bare-metal Windows box (laptop) with 1600 x 900. I could not figure out how to use non-standard video modes on the laptop, so could not try the other way around. The above suggestion would probably work around the bug if it is Microsoft's.

I hope this helps.

[Jim Avera]

Two win10 clients showing "slanty" corruption