Issue with multitouch monitors and xcb_grab/ungrab_pointer.

Nelson, Andrew R. Andrew.R.Nelson at
Mon Oct 28 16:49:57 UTC 2019

Leidos Proprietary

We are encountering an issue with Xorg 1.17.2 (Yes I know it is very old).  

    1. Compile the attached program  [gcc touchbug.c -o touchbug -lxcb]
    2. Run the program [./touchbug ]
    3. Move the mouse over the application window, notice the console output indicates no buttons are pressed.
    4. Press and hold the mouse in the window created by the attached program (this will grab the pointer).
    5. Without releasing the mouse generate a touch event outside of the window (this will ungrab the pointer).
    6. Move the mouse over the window (notice the console output indicates Button1 is pressed). 

I would have expected, in step 6, the console output would again indicate no button is pressed.  

I've tried this with xscope between the example application and the xserver and xscope indicates the motion events sent by the XServer are also reporting Button1 is pressed.    I have though noticed [xinput --query-state <id>] for the mouse indicates all buttons are "up".

It appears this issue has been fixed in Xorg 1.20.4 (at least I'm not seeing the issue on a upgraded workstation that happens to have a later version of Xorg).   

What I'm trying to figure out is what component might be involved in this issue (XServer, XInputExtention, Kernel Driver)?  Is the issue core to the Xserver or is this because the XInput extension has somehow modified the events so that XCB cannot read them correctly?   Is it possible anyone has heard of this issue and can point to where it was fixed?  Is it possible we have somehow misconfigured our XServer?


Andrew Nelson

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