Re: FVWM: Possible bug: Jumping pointer in Darktable

Stefan Klinger <[email protected]> writes:

> I'll be offline for the rest of today (8h driving, yay), so no need to
> hurry...
>
> Dan Espen (2018-Nov-07, excerpt):
>> >> FvwmCommand 'mouse 1 A 4 Beep'
> [...]
>> Fvwm should only Beep when the modifier key is held down.
>
> That's what it does, sorry, should have been more clear about this.
>
>> So, maybe I'm not doing the right thing to see the problem.
>> I've opened darktable,
>
> btw. which Version?  I'm using the master branch, i.e., last time I've
> checked out was
>
>     $ darktable --version
>     this is darktable 2.5.0+767~gabecd987b

$ darktable --version
this is darktable darktable-2.4.4-1.fc27

>> let it import some images, then I double click
>> on one of them.  I then click on the pencil to the left of the image
>
> Hmm, that would be under "mask manager"?
>
>> and I draw a circle on the image.  Then I can use mouse 1 to move
>> the circle around.   The circle moves smoothly and the mouse pointer
>> doesn't jump around.
>
> I've just tried and can observe the error when dragging line sections
> created with the pencil.  Also when creating a circle with the circle
> tool (next to the pencil) and dragging that: jumps.  Interestingly,
> when dragging *nodes* of the line segment created with the pencil, the
> error does not show up.
>
> Honestly, I'm not convinced that this is entirely FVWMs fault...
>
>> I'm not really familiar with Fvwm key binding matching code but I'm
>> willing to look.  But first I think I need to be able to create
>> the problem.
>
> Yeah, totally agree.  maybe it's a quirk in my setup but I would not
> know where to look.  I think I'll try `git bisect` on this to see when
> the bug was introduced.  Not before Friday...

Looking at Fvwm, the first thing Fvwm does with a keybinding like that
is ask X to send mouse events to Fvwm with:

        XGrabButton(
                dpy, button, binding->Modifier, w,
                True, ButtonPressMask |
                ButtonReleaseMask, GrabModeSync,
                GrabModeAsync, None, cursor);

So, this tells X to let Fvwm know about button 1 press and release
events with Modifier 4.  I don't know why that would affect darktable
when Modifier 4 isn't in play.

-- 
Dan Espen