follow up 9a9b53bb:

- enable transform caching (comparing before each use disables its point)
- invalidate the render transform cache only when the layer crs changes by
  connecting to the QgsMapLayer::layerCrsChanged() signal.
- make CRS of map layer private so that setCrs has to be used on each change

src/core/qgsmaplayer.cpp

@@ -513,6 +513,13 @@ const QgsCoordinateReferenceSystem& QgsMapLayer::srs()
 void QgsMapLayer::setCrs( const QgsCoordinateReferenceSystem& srs, bool emitSignal )
 {
   *mCRS = srs;
+
+  if ( !mCRS->isValid() )
+  {
+    mCRS->setValidationHint( tr( "Specify CRS for layer %1" ).arg( name() ) );
+    mCRS->validate();
+  }
+
   if ( emitSignal )
     emit layerCrsChanged();
 }

src/core/qgsmaplayer.h

@@ -235,7 +235,6 @@ class CORE_EXPORT QgsMapLayer : public QObject
     @note emitSignal added in 1.4 */
     void setCrs( const QgsCoordinateReferenceSystem& srs, bool emitSignal = true );
 
-
     /** A convenience function to capitalise the layer name */
     static QString capitaliseLayerName( const QString name );
 
@@ -418,15 +417,15 @@ class CORE_EXPORT QgsMapLayer : public QObject
     /** Name of the layer - used for display */
     QString mLayerName;
 
-    /** layer's Spatial reference system */
-    QgsCoordinateReferenceSystem* mCRS;
-
     QString mTitle;
 
     /**Description of the layer*/
     QString mAbstract;
 
   private:
+    /** layer's spatial reference system.
+        private to make sure setCrs must be used and layerCrsChanged() is emitted */
+    QgsCoordinateReferenceSystem* mCRS;
 
     /** private copy constructor - QgsMapLayer not copyable */
     QgsMapLayer( QgsMapLayer const & );

src/core/qgsmaprenderer.cpp

@@ -680,7 +680,7 @@ void QgsMapRenderer::setDestinationCrs( const QgsCoordinateReferenceSystem& crs
   QgsDebugMsg( "* DestCRS.srsid() = " + QString::number( crs.srsid() ) );
   if ( *mDestCRS != crs )
   {
-    mCachedTrForLayer = 0;
+    invalidateCachedLayerCrs();
     QgsDebugMsg( "Setting DistArea CRS to " + QString::number( crs.srsid() ) );
     mDistArea->setSourceCrs( crs.srsid() );
     *mDestCRS = crs;
@@ -1107,15 +1107,26 @@ void QgsMapRenderer::setLabelingEngine( QgsLabelingEngineInterface* iface )
 
 QgsCoordinateTransform *QgsMapRenderer::tr( QgsMapLayer *layer )
 {
-  // mCachedTrForLayer is unset by setDestinationCrs(), but layer->crs may also be changed after CRS was cached -> check it - the question is, how efficient now the caching is, because crs == operator is not cheap
-  if ( mCachedTrForLayer != layer || layer->crs() != mCachedTr->sourceCrs() )
+  if ( mCachedTrForLayer != layer )
   {
+    invalidateCachedLayerCrs();
+
     delete mCachedTr;
     mCachedTr = new QgsCoordinateTransform( layer->crs(), *mDestCRS );
     mCachedTrForLayer = layer;
+
+    connect( layer, SIGNAL( layerCrsChanged() ), this, SLOT( invalidateCachedLayerCrs() ) );
   }
 
   return mCachedTr;
 }
 
+void QgsMapRenderer::invalidateCachedLayerCrs()
+{
+  if ( mCachedTrForLayer )
+    disconnect( mCachedTrForLayer, SIGNAL( layerCrsChanged() ), this, SLOT( invalidateCachedLayerCrs() ) );
+
+  mCachedTrForLayer = 0;
+}
+
 bool QgsMapRenderer::mDrawing = false;

src/core/qgsmaprenderer.h

@@ -251,6 +251,9 @@ class CORE_EXPORT QgsMapRenderer : public QObject
     //! called by signal from layer current being drawn
     void onDrawingProgress( int current, int total );
 
+    //! invalidate cached layer CRS
+    void invalidateCachedLayerCrs();
+
   protected:
 
     //! adjust extent to fit the pixmap size

src/core/qgsvectorlayer.cpp

@@ -21,16 +21,7 @@
  *                                                                         *
  ***************************************************************************/
 
-#include <cfloat>
-#include <cstring>
-#include <climits>
-#include <cmath>
-#include <iosfwd>
 #include <limits>
-#include <memory>
-#include <set>
-#include <sstream>
-#include <utility>
 
 #include <QImage>
 #include <QPainter>
@@ -2588,11 +2579,11 @@ int QgsVectorLayer::addTopologicalPoints( const QgsPoint& p )
 
   //work with a tolerance because coordinate projection may introduce some rounding
   double threshold =  0.0000001;
-  if ( mCRS && mCRS->mapUnits() == QGis::Meters )
+  if ( crs().mapUnits() == QGis::Meters )
   {
     threshold = 0.001;
   }
-  else if ( mCRS && mCRS->mapUnits() == QGis::Feet )
+  else if ( crs().mapUnits() == QGis::Feet )
   {
     threshold = 0.0001;
   }
@@ -4478,24 +4469,14 @@ void QgsVectorLayer::setCoordinateSystem()
   // for this layer
   //
 
-  // get CRS directly from provider
-  *mCRS = mDataProvider->crs();
-
-  //QgsCoordinateReferenceSystem provides a mechanism for FORCE a srs to be valid
-  //which is inolves falling back to system, project or user selected
-  //defaults if the srs is not properly intialised.
-  //we only nee to do that if the srs is not alreay valid
-  if ( !mCRS->isValid() )
+  if ( hasGeometryType() )
   {
-    if ( hasGeometryType() )
-    {
-      mCRS->setValidationHint( tr( "Specify CRS for layer %1" ).arg( name() ) );
-      mCRS->validate();
-    }
-    else
-    {
-      mCRS->createFromOgcWmsCrs( GEO_EPSG_CRS_AUTHID );
-    }
+    // get CRS directly from provider
+    setCrs( mDataProvider->crs() );
+  }
+  else
+  {
+    setCrs( QgsCoordinateReferenceSystem( GEO_EPSG_CRS_AUTHID ) );
   }
 }
 

src/core/raster/qgsrasterlayer.cpp

@@ -1797,7 +1797,7 @@ QString QgsRasterLayer::metadata()
   myMetadata += tr( "Layer Spatial Reference System: " );
   myMetadata += "</p>\n";
   myMetadata += "<p>";
-  myMetadata += mCRS->toProj4();
+  myMetadata += crs().toProj4();
   myMetadata += "</p>\n";
 
   myMetadata += "<p class=\"glossy\">";
@@ -2224,7 +2224,7 @@ void QgsRasterLayer::setDataProvider( QString const & provider,
                                       QStringList const & layers,
                                       QStringList const & styles,
                                       QString const & format,
-                                      QString const & crs,
+                                      QString const & theCrs,
                                       bool loadDefaultStyleFlag )
 {
   Q_UNUSED( loadDefaultStyleFlag );
@@ -2251,13 +2251,15 @@ void QgsRasterLayer::setDataProvider( QString const & provider,
   }
 
 
-  QgsDebugMsg( "Instantiated the data provider plugin"
-               + QString( " with layer list of " ) + layers.join( ", " )
-               + " and style list of " + styles.join( ", " )
-               + " and format of " + format +  " and CRS of " + crs );
+  QgsDebugMsg( QString( "Instantiated the data provider plugin with layer list of %1 and style list of %2 and format of %3 and CRS of %4" )
+               .arg( layers.join( ", " ) )
+               .arg( styles.join( ", " ) )
+               .arg( format )
+               .arg( theCrs )
+             );
   if ( !mDataProvider->isValid() )
   {
-    if ( provider != "gdal" || !layers.isEmpty() || !styles.isEmpty() || !format.isNull() || !crs.isNull() )
+    if ( provider != "gdal" || !layers.isEmpty() || !styles.isEmpty() || !format.isNull() || !theCrs.isNull() )
     {
       QgsMessageLog::logMessage( tr( "Data provider is invalid (layers %1, styles %2, formats: %3)" )
                                  .arg( layers.join( ", " ) )
@@ -2270,7 +2272,7 @@ void QgsRasterLayer::setDataProvider( QString const & provider,
 
   mDataProvider->addLayers( layers, styles );
   mDataProvider->setImageEncoding( format );
-  mDataProvider->setImageCrs( crs );
+  mDataProvider->setImageCrs( theCrs );
 
   setNoDataValue( mDataProvider->noDataValue() );
 
@@ -2299,21 +2301,16 @@ void QgsRasterLayer::setDataProvider( QString const & provider,
   // Setup source CRS
   if ( mProviderKey == "wms" )
   {
-    *mCRS = QgsCoordinateReferenceSystem();
-    mCRS->createFromOgcWmsCrs( crs );
+    QgsCoordinateReferenceSystem crs;
+    crs.createFromOgcWmsCrs( theCrs );
+    setCrs( crs );
   }
   else
   {
-    *mCRS = QgsCoordinateReferenceSystem( mDataProvider->crs() );
+    setCrs( QgsCoordinateReferenceSystem( mDataProvider->crs() ) );
   }
-  //get the project projection, defaulting to this layer's projection
-  //if none exists....
-  if ( !mCRS->isValid() )
-  {
-    mCRS->setValidationHint( tr( "Specify CRS for layer %1" ).arg( name() ) );
-    mCRS->validate();
-  }
-  QString mySourceWkt = mCRS->toWkt();
+
+  QString mySourceWkt = crs().toWkt();
 
   QgsDebugMsg( "using wkt:\n" + mySourceWkt );