Allow QgsMapLayer::triggerRepaint to defer updates

By calling QgsMapLayer::triggerRepaint( true ) any cached
version of the layer will be invalidated, but a map canvas
refresh won't automatically be triggered

This allows invalidation of cached images while deferring
the actual map update until the next canvas refresh.

python/core/qgsmaplayer.sip

@@ -634,13 +634,7 @@ class QgsMapLayer : QObject
      */
     void setScaleBasedVisibility( const bool enabled );
 
-    /**
-     * Will advice the map canvas (and any other interested party) that this layer requires to be repainted.
-     * Will emit a repaintRequested() signal.
-     *
-     * @note in 2.6 function moved from vector/raster subclasses to QgsMapLayer
-     */
-    void triggerRepaint();
+    void triggerRepaint( bool deferredUpdate = false );
 
     /** \brief Obtain Metadata for this layer */
     virtual QString metadata() const;
@@ -687,10 +681,7 @@ class QgsMapLayer : QObject
     /** Emit a signal that layer's CRS has been reset */
     void crsChanged();
 
-    /** By emitting this signal the layer tells that either appearance or content have been changed
-     * and any view showing the rendered layer should refresh itself.
-     */
-    void repaintRequested();
+    void repaintRequested( bool deferredUpdate = false );
 
     /** This is used to send a request that any mapcanvas using this layer update its extents */
     void recalculateExtents() const;

src/app/qgisapp.cpp

@@ -10408,7 +10408,7 @@ void QgisApp::layersWereAdded( const QList<QgsMapLayer *>& theLayers )
 
     if ( provider )
     {
-      connect( provider, &QgsDataProvider::dataChanged, layer, &QgsMapLayer::triggerRepaint );
+      connect( provider, &QgsDataProvider::dataChanged, layer, [layer] { layer->triggerRepaint(); } );
       connect( provider, &QgsDataProvider::dataChanged, mMapCanvas, &QgsMapCanvas::refresh );
     }
   }

src/browser/qgsbrowser.cpp

@@ -439,7 +439,7 @@ void QgsBrowser::updateCurrentTab()
       QgsRasterLayer *rlayer = qobject_cast< QgsRasterLayer * >( mLayer );
       if ( rlayer )
       {
-        connect( rlayer->dataProvider(), &QgsRasterDataProvider::dataChanged, rlayer, &QgsRasterLayer::triggerRepaint );
+        connect( rlayer->dataProvider(), &QgsRasterDataProvider::dataChanged, rlayer, [rlayer] { rlayer->triggerRepaint(); } );
         connect( rlayer->dataProvider(), &QgsRasterDataProvider::dataChanged, mapCanvas, &QgsMapCanvas::refresh );
       }
     }

src/core/qgsmaplayer.cpp

@@ -1591,9 +1591,9 @@ QgsMapLayerStyleManager* QgsMapLayer::styleManager() const
   return mStyleManager;
 }
 
-void QgsMapLayer::triggerRepaint()
+void QgsMapLayer::triggerRepaint( bool deferredUpdate )
 {
-  emit repaintRequested();
+  emit repaintRequested( deferredUpdate );
 }
 
 QString QgsMapLayer::metadata() const

src/core/qgsmaplayer.h

@@ -678,12 +678,14 @@ class CORE_EXPORT QgsMapLayer : public QObject
     void setScaleBasedVisibility( const bool enabled );
 
     /**
-     * Will advice the map canvas (and any other interested party) that this layer requires to be repainted.
+     * Will advise the map canvas (and any other interested party) that this layer requires to be repainted.
      * Will emit a repaintRequested() signal.
+     * If \a deferredUpdate is true then the layer will only be repainted when the canvas is next
+     * re-rendered, and will not trigger any canvas redraws itself.
      *
      * @note in 2.6 function moved from vector/raster subclasses to QgsMapLayer
      */
-    void triggerRepaint();
+    void triggerRepaint( bool deferredUpdate = false );
 
     //! \brief Obtain Metadata for this layer
     virtual QString metadata() const;
@@ -732,8 +734,10 @@ class CORE_EXPORT QgsMapLayer : public QObject
 
     /** By emitting this signal the layer tells that either appearance or content have been changed
      * and any view showing the rendered layer should refresh itself.
+     * If \a deferredUpdate is true then the layer will only be repainted when the canvas is next
+     * re-rendered, and will not trigger any canvas redraws itself.
      */
-    void repaintRequested();
+    void repaintRequested( bool deferredUpdate = false );
 
     //! This is used to send a request that any mapcanvas using this layer update its extents
     void recalculateExtents() const;

src/core/qgsvectorlayer.cpp

@@ -164,7 +164,7 @@ QgsVectorLayer::QgsVectorLayer( const QString& vectorLayerPath,
     setDataSource( vectorLayerPath, baseName, providerKey, loadDefaultStyleFlag );
   }
 
-  connect( this, &QgsVectorLayer::selectionChanged, this, &QgsVectorLayer::repaintRequested );
+  connect( this, &QgsVectorLayer::selectionChanged, this, [=]{ emit repaintRequested(); } );
   connect( QgsProject::instance()->relationManager(), &QgsRelationManager::relationsLoaded, this, &QgsVectorLayer::onRelationsLoaded );
 
   // Default simplify drawing settings

src/gui/qgsmapcanvas.cpp

@@ -295,7 +295,7 @@ void QgsMapCanvas::setLayers( const QList<QgsMapLayer*>& layers )
 
   Q_FOREACH ( QgsMapLayer* layer, oldLayers )
   {
-    disconnect( layer, &QgsMapLayer::repaintRequested, this, &QgsMapCanvas::refresh );
+    disconnect( layer, &QgsMapLayer::repaintRequested, this, &QgsMapCanvas::layerRepaintRequested );
     disconnect( layer, &QgsMapLayer::crsChanged, this, &QgsMapCanvas::layerCrsChange );
     if ( QgsVectorLayer* vlayer = qobject_cast<QgsVectorLayer *>( layer ) )
     {
@@ -307,7 +307,7 @@ void QgsMapCanvas::setLayers( const QList<QgsMapLayer*>& layers )
 
   Q_FOREACH ( QgsMapLayer* layer, layers )
   {
-    connect( layer, &QgsMapLayer::repaintRequested, this, &QgsMapCanvas::refresh );
+    connect( layer, &QgsMapLayer::repaintRequested, this, &QgsMapCanvas::layerRepaintRequested );
     connect( layer, &QgsMapLayer::crsChanged, this, &QgsMapCanvas::layerCrsChange );
     if ( QgsVectorLayer* vlayer = qobject_cast<QgsVectorLayer *>( layer ) )
     {
@@ -1668,6 +1668,12 @@ void QgsMapCanvas::updateDatumTransformEntries()
   }
 }
 
+void QgsMapCanvas::layerRepaintRequested( bool deferred )
+{
+  if ( !deferred )
+    refresh();
+}
+
 
 
 QgsMapTool* QgsMapCanvas::mapTool()

src/gui/qgsmapcanvas.h

@@ -612,6 +612,10 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
     //! Make sure the datum transform store is properly populated
     void updateDatumTransformEntries();
 
+  private slots:
+
+    void layerRepaintRequested( bool deferred );
+
   private:
     /// this class is non-copyable
 

src/gui/qgsmapoverviewcanvas.cpp

@@ -207,9 +207,10 @@ void QgsMapOverviewCanvas::mapRenderingFinished()
   update();
 }
 
-void QgsMapOverviewCanvas::layerRepaintRequested()
+void QgsMapOverviewCanvas::layerRepaintRequested( bool deferred )
 {
-  refresh();
+  if ( !deferred )
+    refresh();
 }
 
 

src/gui/qgsmapoverviewcanvas.h

@@ -75,7 +75,11 @@ class GUI_EXPORT QgsMapOverviewCanvas : public QWidget
 
   protected slots:
     void mapRenderingFinished();
-    void layerRepaintRequested();
+
+    /**
+     * Triggered when a layer in the overview requests a repaint.
+     */
+    void layerRepaintRequested( bool deferred = false );
 
   protected: