[composer] Fix incorrect calculation of map bounds when a map is switched to atlas control after atlas preview is enabled

Author: nyalldawson

src/core/composer/qgsatlascomposition.cpp

@@ -443,38 +443,43 @@ void QgsAtlasComposition::prepareForFeature( int featureI )
     atlasMaps << currentMap;
   }
 
+  //clear the transformed bounds of the previous feature
+  mTransformedFeatureBounds = QgsRectangle();
+
   if ( atlasMaps.isEmpty() )
   {
     //no atlas enabled maps
     return;
   }
 
-  //
-  // compute the new extent
-  // keep the original aspect ratio
-  // and apply a margin
-
-  const QgsCoordinateReferenceSystem& coverage_crs = mCoverageLayer->crs();
-  // transformation needed for feature geometries. This should be set on a per-atlas map basis,
+  // compute extent of current feature in the map CRS. This should be set on a per-atlas map basis,
   // but given that it's not currently possible to have maps with different CRSes we can just
   // calculate it once based on the first atlas maps' CRS.
-  const QgsCoordinateReferenceSystem& destination_crs = atlasMaps[0]->mapRenderer()->destinationCrs();
+  computeExtent( atlasMaps[0] );
+
+  //update atlas bounds of every atlas enabled composer map
+  for ( QList<QgsComposerMap*>::iterator mit = atlasMaps.begin(); mit != atlasMaps.end(); ++mit )
+  {
+    prepareMap( *mit );
+  }
+}
+
+void QgsAtlasComposition::computeExtent( QgsComposerMap* map )
+{
+  // compute the extent of the current feature, in the crs of the specified map
+
+  const QgsCoordinateReferenceSystem& coverage_crs = mCoverageLayer->crs();
+  // transformation needed for feature geometries
+  const QgsCoordinateReferenceSystem& destination_crs = map->mapRenderer()->destinationCrs();
   mTransform.setSourceCrs( coverage_crs );
   mTransform.setDestCRS( destination_crs );
 
   // QgsGeometry::boundingBox is expressed in the geometry"s native CRS
   // We have to transform the grometry to the destination CRS and ask for the bounding box
   // Note: we cannot directly take the transformation of the bounding box, since transformations are not linear
-
   QgsGeometry tgeom( *mCurrentFeature.geometry() );
   tgeom.transform( mTransform );
   mTransformedFeatureBounds = tgeom.boundingBox();
-
-  //update atlas bounds of every atlas enabled composer map
-  for ( QList<QgsComposerMap*>::iterator mit = atlasMaps.begin(); mit != atlasMaps.end(); ++mit )
-  {
-    prepareMap( *mit );
-  }
 }
 
 void QgsAtlasComposition::prepareMap( QgsComposerMap* map )
@@ -484,6 +489,13 @@ void QgsAtlasComposition::prepareMap( QgsComposerMap* map )
     return;
   }
 
+  if ( mTransformedFeatureBounds.isEmpty() )
+  {
+    //transformed extent of current feature hasn't been calculated yet. This can happen if
+    //a map has been set to be atlas controlled after prepare feature was called
+    computeExtent( map );
+  }
+
   double xa1 = mTransformedFeatureBounds.xMinimum();
   double xa2 = mTransformedFeatureBounds.xMaximum();
   double ya1 = mTransformedFeatureBounds.yMinimum();

src/core/composer/qgsatlascomposition.h

@@ -201,6 +201,9 @@ class CORE_EXPORT QgsAtlasComposition : public QObject
 
     //forces all atlas enabled maps to redraw
     void updateAtlasMaps();
+
+    //computes the extent of the current feature, in the crs of the specified map
+    void computeExtent( QgsComposerMap *map );
 };
 
 #endif