[racket-dev] gui responsiveness

You're right that it's about event ordering and not refresh coalescing.
Since mouse events are handled after refreshes, you won't get the next
refresh request until an earlier one is handled, after which the next
mouse event can trigger another refresh request. I think the difference
between Unix/X and Windows may be that Windows sends fewer mouse
events.

There are trade-offs here, but my experience is that ordering input
events before refresh does not work well in general. To trigger
refreshes at a lower priority in this case, you could use Neil's
suggestion or change

 (send this refresh)

to

 (set! needed? #t)
 (queue-callback (lambda () (when needed?
                              (set! needed? #f)
                              (send this refresh)))
                 #f) ; => low priority

where `needed?` is a field that's initially #f.

At Wed, 16 Apr 2014 13:33:02 -0400, David Vanderson wrote:
> (moved to dev)
> 
> On Linux, the attached program shows terrible responsiveness when 
> dragging points around on the graph.  Can anyone else on Linux reproduce 
> this behavior?
> 
> 
> The patch below dramatically improves the responsiveness by forcing the 
> eventspace to process medium-level events (mouse movement) before 
> refresh events.  Without the patch, each mouse drag causes a paint.  
> With it, multiple mouse drags are processed before a paint.
> 
> 
> I'm unsure about this fix.  Windows doesn't show the problem (I don't 
> have a mac to test), so I think it's just a GTK issue.
> 
> My guess is that the gui layer is relying on the native libraries to 
> coalesce multiple refresh requests (but this is not working with GTK).  
> Can anyone confirm this?
> 
> Thanks,
> Dave
> 
> 
> 
> diff -ru 
> racket-6.0_clean/share/pkgs/gui-lib/mred/private/wx/common/queue.rkt 
> racket-6.0/share/pkgs/gui-lib/mred/private/wx/common/queue.rkt
> --- racket-6.0_clean/share/pkgs/gui-lib/mred/private/wx/common/queue.rkt 
> 2014-02-18 12:27:43.000000000 -0500
> +++ racket-6.0/share/pkgs/gui-lib/mred/private/wx/common/queue.rkt 
> 2014-04-16 09:41:16.810993955 -0400
> @@ -300,8 +300,8 @@
> (lambda (_) #f))
>                                              (or (first hi peek?)
> (timer-first-ready timer peek?)
> -                                               (first refresh peek?)
>                                                  (first med peek?)
> +                                               (first refresh peek?)
>                                                  (and (not peek?)
>                                                       sync?
>                                                       ;; before going 
> with low-priority events,
> 
> 
> ------------------------------------------------------------------------------
> [text/plain "graph_ui.rkt"] [~/Desktop & open] [~/Temp & open]
> _________________________
>   Racket Developers list:
>   http://lists.racket-lang.org/dev