[winswitch] Pressing alt sometimes generates space characters, and dragging window is unreliable

Antoine Martin antoine at nagafix.co.uk
Sat May 23 04:37:39 BST 2020

On 23/05/2020 07:35, Joakim Ziegler via shifter-users wrote:
> I've installed Xpra 4.0.1 on the server (Ubuntu 20.04) and Xpra 3.0.9 on
> the client (Centos 7.7.1908), and I'm using it to run Chrome, we're
> currently in testing, and everything seems to be working fine, apart from
> two fairly minor problems:
> We use Chrome in large part for accessing Google Docs, and we noticed a
> strange problem. Sometimes when pressing Alt-Tab to switch windows, the
> current cell in Google Sheets would blank, that is, the contents would be
> replaced by one or more space characters. At first we thought this was
> something that happens when switching windows, but it turns out, it's
> something that happens irregularly when pressing Alt.
Modifier keys are a pain to synchronize generally, Alt-Tabbing away
brings its own set of problems: since the window is no longer in focus
after Alt-Tab, the key release events go missing.

> If you open Google Docs and move around between cells with contents in them
> by clicking the mouse, and then press Alt, some times (one out of five,
> maybe), pressing Alt will generate space key presses, which blanks out the
> cells. This only happens after having used the mouse to click on the cells,
> and what's stranger, even if it doesn't happen every time, when it does
> happen, the number of space key presses generated seems to be proportional
> to the number of times you've pressed Alt before this happens, so if it
> happens after trying to provoke it three times, you'll get three space
> characters.
> Is this a known bug?
No. This one I was not aware of.

> Might it be a result of using 3.0.9 on the client and
> 4.0.1 on the server?

> I'm happy to generate a formal bug report, but I
> wanted to know if this was a known problem that might be solved by an
> upgrade first.
Please create a ticket.
> Secondly, and this is less important, when dragging the Chrome window by
> the title bar, the first time you drag, it works fine, but if you release
> the mouse button and then immediately try to drag the window again, it
> won't move. It'll move again on the third attempt, then not on the fourth,
> and so on. I'm also wondering if this is a known problem, and/or related to
> using 3.0.9 on the client.
That's probably something to do with the button state not getting
synchronized properly: the server or the application never sees the
button being released, so the next button press doesn't do anything.
I have seen this with the html5 client before, not so much with the X11
python client.
Would you mind creating another ticket for this?

Both bugs should be fixable given precise and preferably simple steps to
reproduce them.


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