fix #3742:

- after CRS changes reproject canvas extent regardless of OTFR
- toggling OTFR off, switches the project CRS to the current layer CRS (or
  first layer, if no layer is active).
- toggling OTFR also saves the previous CRS setting and restores the previous
  selected CRS.

Author: jef-n

src/app/qgsprojectproperties.cpp

@@ -41,7 +41,8 @@
 
 
 QgsProjectProperties::QgsProjectProperties( QgsMapCanvas* mapCanvas, QWidget *parent, Qt::WFlags fl )
-    : QDialog( parent, fl ), mMapCanvas( mapCanvas )
+    : QDialog( parent, fl )
+    , mMapCanvas( mapCanvas )
 {
   setupUi( this );
   connect( buttonBox, SIGNAL( accepted() ), this, SLOT( accept() ) );
@@ -63,9 +64,9 @@ QgsProjectProperties::QgsProjectProperties( QgsMapCanvas* mapCanvas, QWidget *pa
   cbxProjectionEnabled->setChecked( myProjectionEnabled );
   btnGrpMapUnits->setEnabled( !myProjectionEnabled );
 
-  long myCRSID = myRenderer->destinationCrs().srsid();
-  QgsDebugMsg( "Read project CRSID: " + QString::number( myCRSID ) );
-  projectionSelector->setSelectedCrsId( myCRSID );
+  mProjectSrsId = myRenderer->destinationCrs().srsid();
+  QgsDebugMsg( "Read project CRSID: " + QString::number( mProjectSrsId ) );
+  projectionSelector->setSelectedCrsId( mProjectSrsId );
 
   ///////////////////////////////////////////////////////////
   // Properties stored in QgsProject
@@ -112,6 +113,19 @@ QgsProjectProperties::QgsProjectProperties( QgsMapCanvas* mapCanvas, QWidget *pa
 
   const QMap<QString, QgsMapLayer*> &mapLayers = QgsMapLayerRegistry::instance()->mapLayers();
 
+  if ( mMapCanvas->currentLayer() )
+  {
+    mLayerSrsId = mMapCanvas->currentLayer()->crs().srsid();
+  }
+  else if ( mapLayers.size() > 0 )
+  {
+    mLayerSrsId = mapLayers.begin().value()->crs().srsid();
+  }
+  else
+  {
+    mLayerSrsId = mProjectSrsId;
+  }
+
   twIdentifyLayers->setColumnCount( 3 );
   twIdentifyLayers->horizontalHeader()->setVisible( true );
   twIdentifyLayers->setHorizontalHeaderItem( 0, new QTableWidgetItem( tr( "Layer" ) ) );
@@ -454,6 +468,17 @@ void QgsProjectProperties::on_pbnCanvasColor_clicked()
 void QgsProjectProperties::on_cbxProjectionEnabled_stateChanged( int state )
 {
   btnGrpMapUnits->setEnabled( state == Qt::Unchecked );
+
+  if ( state != Qt::Checked )
+  {
+    mProjectSrsId = projectionSelector->selectedCrsId();
+    projectionSelector->setSelectedCrsId( mLayerSrsId );
+  }
+  else
+  {
+    mLayerSrsId = projectionSelector->selectedCrsId();
+    projectionSelector->setSelectedCrsId( mProjectSrsId );
+  }
 }
 
 void QgsProjectProperties::setMapUnitsToCurrentProjection()
@@ -541,7 +566,9 @@ void QgsProjectProperties::on_pbnWMSAddSRS_clicked()
 void QgsProjectProperties::on_pbnWMSRemoveSRS_clicked()
 {
   foreach( QListWidgetItem *item, mWMSList->selectedItems() )
-  delete item;
+  {
+    delete item;
+  }
 }
 
 void QgsProjectProperties::on_pbnWMSSetUsedSRS_clicked()

src/app/qgsprojectproperties.h

@@ -123,4 +123,7 @@ class QgsProjectProperties : public QDialog, private Ui::QgsProjectPropertiesBas
      * Function to restore dialog window state
      */
     void restoreState();
+
+    long mProjectSrsId;
+    long mLayerSrsId;
 };

src/core/qgsmaprenderer.cpp

@@ -683,7 +683,7 @@ void QgsMapRenderer::setDestinationCrs( const QgsCoordinateReferenceSystem& crs
   if ( *mDestCRS != crs )
   {
     QgsRectangle rect;
-    if ( hasCrsTransformEnabled() && !mExtent.isEmpty() )
+    if ( !mExtent.isEmpty() )
     {
       QgsCoordinateTransform transform( *mDestCRS, crs );
       rect = transform.transformBoundingBox( mExtent );