bug#36779: 25.1; mouse click not recognized for frames with large left position

[Eijiro Sumii]

On Tue, Jul 30, 2019 at 4:01 PM martin rudalics <rudalics@gmx.at> wrote:
>  >> Can you mark text with the mouse?
>  > No, I cannot.
> So the mouse down event is probably not recognized.

In fact, it seems partially recognized.  I find the situation with
split windows (C-x 3) even weirder - too weird that I cannot explain
in text, so forgive me for the Dropbox link to a ~100 MB movie (with
sounds of the mouse button up and down - sorry for my unstable left
hand!):

https://www.dropbox.com/s/dbzigg9qggkyvig/IMG_6263.MOV?dl=0

As you can see, the behavior of mouse clicks on the right split window
seems almost random.  The environment is:

- My left 1920x1080 monitor is
https://www.dropbox.com/s/32f4pijigil3dgf/IMG_6260.JPG?dl=0

- My right 3840x2160 monitor is
https://www.dropbox.com/s/2advpxq1988uxac/IMG_6259.JPG?dl=0

- The border between the split windows of Emacs is slightly to the
right of the center of the right monitor.

- The X server treats the two monitors like a single 5760x2160 monitor.

- Given that, there seems nothing wrong with the output of xdpyinfo
and (display-monitor-attributes-list).

- There also seems nothing wrong with other X clients or GTK applications.

An additional (perhaps important) observation is:

- The problem occurs only when the right display is added after the X
server (and its first X client - mlterm in my case) started.

>  > I haven't yet pursued further executions (I need to sit in front of the
>  > second, 60-inch 4K display for this!), but will do (so, advice is 
> welcome!).
>
> The subsequent code is among the most convoluted ones Emacs has,
> sprinkled with USE_GTK, USE_X_TOOLKIT and USE_TOOLKIT_SCROLL_BARS
> defines, so you have all my sympathy.  But maybe stepping into
> x_window_to_frame already exhibits that the latter is not able to find
> a suitable frame ...

The code is fine, but I just cannot carry the 60-inch monitor with me
to other places (lecture halls, meeting rooms, cafe, home, etc.) and
have to find time:-) to sit in my office to investigate this (but I
will continue to look into what's happening)!:-)