[Matplotlib-users] Double Buffering (was: Gtk.Notebook problem in PyGTK 2.6)

[N. V. <mit...@we...>]

[...]

>> On 5/31/05, *John Gill* <jn...@eu... 
>> <mailto:jn...@eu...>> wrote:
>>
>>     I think this might be a matplotlib issue.
>>
>>     I've been having some refresh issues with matplotlib since
>>     switching to 2.6.  In particular I've noticed that if I put my
>>     mouse over the toolbar and let a tooltip pop up the canvas does
>>     not get repainted.
>>
>>     Up to now I'd been assuming this problem was isolated to me (I use
>>     ratpoison as a window manager, which can confuse some apps).
>>
>>     I've cc'ed the matplotlib list in case anyone can throw some light
>>     on this.
>>
>>     John
>>
[...]

> I can confirm this (mis)behaviour with matplotlib 0.80 and gtk+/pygtk 
> 2.6.  I had wanted to look into this matter, but didn't yet have time 
> to do it.  A simple guess would be that the expose-event is not 
> handled properly by the GTK backend.
>
> I noticed the problem when I put a menu-bar over a matplotlib GTK 
> Canvas.  When you leave an opened menu, the menu will not disappear.
>
> Niklas.
>

I have started looking at the code and did not quite understand what I 
found:

backends/backend_gtk.py has a class FigureCanvasGTK. Its method 
'expose_event' is responsible for redrawing.
In the situation I described, when I leave an opened menu that overlaps 
the graph, the expose_event is properly called, but the widget is not 
redrawn. If DBL_BUFFER is set (which it is), the widget is only redrawn, 
if self._draw_pixmap is set to True. Of course, this variable is not set 
to True when GTK closes a menu but only when matplotlib requests a 
redraw.  So, in conclusion, no redraw happens.

After consulting the PyGTK reference I tried to reactivate double 
buffering, which is turned of in the backend_gtk.py by the command

self.set_double_buffered(False)

I wonder why you set this? Do you want to provide your own double 
buffering? Why? If you set this value to True, everything will be fine.

Best regards,

Niklas Volbers.