[QGIS-trac] [Quantum GIS] #1716: improvements to ZoomLast, ZoomNext tools (extent history)

[Quantum GIS]

#1716: improvements to ZoomLast, ZoomNext tools (extent history)
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   Reporter:  smizuno                          |              Owner:  nobody
       Type:  patch                            |             Status:  new   
   Priority:  minor: annoyance or enhancement  |          Milestone:        
  Component:  GUI                              |            Version:  HEAD  
   Keywords:                                   |   Platform_version:        
   Platform:  All                              |           Must_fix:  No    
Status_info:  0                                |  
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 I have found the addition of the view extent history using the
 ZoomLast/ZoomNext tools to be very useful. However, because there was no
 status indicated on the buttons it was not easy to tell whether there was
 an extent to zoom to.

 Also, I found that loading a project did not set its extent in the history
 list.

 I believe the extent history should be cleared when a project (new or
 existing) is loaded because the map extent is set to the extent of a
 project or the first layer loaded making this point the logical beginning
 for the extent history.

 Some people might argue that the previous view extents might be useful
 with a new project or even an existing project, but I believe that it is
 more likely that these extents are of little use.

 Note that on program start, the map extent is set twice - once by fileNew,
 then by the command-line extent processing - so there are two extents in
 the history instead of one.

 I provide a patch to do the following:

 Improvements-

 + to make the ZoomLast and ZoomNext buttons show whether there is an
 extent to zoom to (in various functions, signals are emitted to update the
 button state)

 + provide a new function to clear the extent history and set the current
 extent as the first item: QgsMapCanvas::clearExtentHistory()

 + clear the extent history on new project (this is mostly cosmetic as
 other actions will also clear the history)

 + clear the extent history when the first layer is loaded

 + clear the extent history on project loading (the extent is set in
 QgsMapRenderer, but the list of extents wasn't updated)

 minor updates in QgsMapCanvas -

 + in zoomToPreviousExtent() and zoomToNextExtent(): refresh() was moved
 inside the if block so that it is called only if there is a previous or
 next extent (this doesn't mean much when the now disabled button won't
 allow a click event in such a case, but was an unnecessary map redraw
 before the button got status indication)

 + in zoomToPreviousExtent(): mLastExtentIndex was tested for >1 -- it
 should be >0.

 qgsmapcanvas.sip is updated for the new function and signals, so Python
 can make use of them.

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/1716>
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