[QGIS-trac] Re: [Quantum GIS] #1016: mysterious white box obscures data in the map window

[Quantum GIS]

#1016: mysterious white box obscures data in the map window
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        Reporter:  rgaston                           |         Owner:  mhugent                           
            Type:  patch                             |        Status:  reopened                          
        Priority:  major: does not work as expected  |     Milestone:  Version 1.0.0                     
       Component:  Graphics                          |       Version:  HEAD                              
      Resolution:                                    |      Keywords:  obscuring box, digitizing, zooming
Platform_version:                                    |      Platform:  All                               
        Must_fix:  No                                |   Status_info:  0                                 
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Changes (by smizuno):

  * status:  closed => reopened
  * resolution:  fixed =>

Comment:

 I reopen this ticket as I now have a good explanation of why the problem
 occurs and a further patch to fix it.

 After reviewing (again... and again) the QGraphicsScene and QGraphicsItem
 classes, I found that prepareGeometryChange() needs to be called before
 changing a QGraphicsItem's geometry.

 This is the root cause of the white boxes (artifacts of rubberbands and
 other objects) on the map canvas. The mapcanvasmap had its size changed,
 but the mapcanvas didn't know about it, therefore not redrawing its
 objects at the new size.

 I have tested this by reverting to the previous order in QgsMapCanvas
 where the scene size was set, then the map size was set. Then
 prepareGeometryChange() is called in QgsMapCanvasMap::resize(). Now, there
 are no artifacts.

 Still, it is better that the scene size is set after the map size is
 changed, as the scene size change updates indexes as necessary.

 The patch provided adds the prepareGeometryChange() call in
 QgsMapCanvasMap::resize() and updates the note about the problem in
 QgsMapCanvas::resizeEvent().

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/1016#comment:8>
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