[xmonad] darcs patch: quick hack to avoid infinite (but breakable) loop when...

[Klaus Weidner]

I've tried the change described below (see attached patch), and it
works for me, and appears to also make xmonad react a lot faster to
mouse movement due to skipping unnecessary refocusing. Can others
please check if it causes any regressions for them?

-Klaus

On Sat, May 17, 2008 at 11:18 AM, Klaus Weidner <kweidner at pobox.com> wrote:
> On Sat, May 17, 2008 at 05:09:41AM -0700, David Roundy wrote:
>> On Sat, May 17, 2008 at 03:12:49AM -0700, Klaus Weidner wrote:
>> > The unpatched behaviour restored by your patch is to clear the step (b)
>> > enter event. However, that does the wrong thing if moving the mouse
>> > quickly across multiple windows A-B-C, in that case B keeps the focus
>> > even though the mouse ended in window C.
>>
>> I've never observed this, myself.  Perhaps it requires an even slower
>> computer than mine, or maybe a really slow layout?
>
> The notebook I saw this on is pretty fast (Core 2 Duo), and I commonly
> saw this with a moderately complex (but not unreasonable) dualscreen
> setup including combineTwo and tabs on one screen, something like this:
>
>     Screen A                              Screen B
>     -- firefox windows --  -- other -
>     [tab][tab][tab][tab] | [tab][tab]     [any layout]
>
> Moving the mouse from screen B to the "firefox" tab section on the left
> would often get focus stuck on the "other" tab, and I was often closing
> the wrong window when intending to close a browser window. I did
> generally have my 9 workspaces filled with windows and updating layouts
> takes a noticeable amount of time. If I understand it right, the
> not-visible windows still slow down the recomputations.
>
>> > Probably the right thing to do would be to clear the pending crossing
>> > events in 'windows' whenever the layout manipulation moves/resizes/remaps
>> > windows, and not clear it if only the focus has changed. What would be
>> > a clean way to make that distinction?
>>
>> Probably a better option would be to not clear crossing events at all, but
>> instead when we handle crossing events to first check if the mouse is still
>> in the said window.  If it's not, then we should ignore the event.
>
> That sounds reasonable - how about a something like the following (not a
> real patch - I'm still away from my computer including next week and
> can't test this):
>
> XMonad/Main.hs:
>  handle e@(CrossingEvent {ev_window = w, ev_event_type = t})
>     | t == enterNotify && ev_mode   e == notifyNormal
>                        && ev_detail e /= notifyInferior
> -    = whenX (asks $ focusFollowsMouse . config) (focus w)
> +    = whenX (asks $ focusFollowsMouse . config) $ do
> +        dpy <- asks display
> +        root <- asks theRoot
> +        (_,_,w',_,_,_,_,_) <- io $ queryPointer dpy root
> +        when (w == w') (focus w)
>
> XMonad/Operations.hs:
>     mapM_ (flip setWMState withdrawnState) (W.allWindows old \\ W.allWindows ws)
> -
> -    unless isMouseFocused $ clearEvents enterWindowMask
>
>
> The change should be noticeable if you put a large number of windows on
> the screen and quickly move the mouse across them. The three behaviors to
> look for would be:
>
> - focus stays in one of the first windows entered (before the
>  mouseFocused patch)
>
> - each window crossed briefly gets focused (the border flashes), with
>  focus staying in the final one (with mouseFocused patch)
>
> - the final window gets focused, and maybe one or two of the ones crossed
>  along the way, but most skip getting focused along the way (hopefully
>  the new behavior with the above change)
>
> -Klaus
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