Re: [Matplotlib-users] Plot moves while using the "Zoom to rectangle" button

[João L. S. <js...@fc...>]

On 07/13/2010 02:31 AM, John Hunter wrote:
> On Mon, Jul 12, 2010 at 8:05 PM, John Hunter<jd...@gm...>  wrote:
>> All of which is discouraging: we both see bugs but different ones on
>> linux, the appearance of the bug is caused by adding a combobox which
>> is not used (on my system), the bug appears on some platforms (linux)
>> but not others (win) and it appears for both gtk and gtkagg.
>
> The last thing I'll add for now is that my bug, the black pixel noise
> (fills the axes window when motion starts in a zoom-to-rect event)
> which may be unrelated to your bug, is happening in
> backend_gtk.NavigationToolbar2GTK.draw_rubberband in the pair of
> calls:
>
>    # this is used to copy the background that the zoom to rect
> "rubberband" will be drawn over
>    self._imageBack = axrect, drawable.get_image(*axrect)
>
>    # this is used to restore the background before redrawing the
> rectangle for the zoom box
>    drawable.draw_image(gc, imageBack, 0, 0, *lastrect)
>
> Since the bug is only exposed when a combo box is added to the
> hierarchy, and appears to be platform or gtk specific, I'm suspecting
> a gtk bug at this point.  But I don't have anything conclusive or a
> minimal example which I could use to post to the gtk list.  The mpl
> calls and values (axrect, lastrect, etc) look correct on inspection.
> Somehow the call to drawable.get_image is getting a buffer full of
> noise if and only if the combobox is added to the vbox.
>
> JDH

 From what I could understand from the pygtk documentation get_image / 
draw_image are client-side operations. In particular:

"If the source drawable is a Gdk::Window and partially offscreen or 
obscured, then the obscured portions of the returned image will contain 
undefined data."

Anyway they recommend using Pixmap, which is server-side and a offscreen 
drawable. I've attached a patch that replaces the get_image / draw_image 
with Pixmap operations and fixes this bug. I've tested this patch on 
Linux and Windows.

Regards,
João Luís