[composer] Instant feedback for legend when linked map changes

(cherry-picked from f9ff5e2)

Author: nyalldawson

src/core/composer/qgscomposerlegend.cpp

@@ -306,7 +306,7 @@ void QgsComposerLegend::updateLegend()
 
 void QgsComposerLegend::updateItem()
 {
-  updateFilterByMap();
+  updateFilterByMap( false );
   QgsComposerItem::updateItem();
 }
 
@@ -605,7 +605,7 @@ void QgsComposerLegend::mapLayerStyleOverridesChanged()
   {
     // legend is being filtered by map, so we need to re run the hit test too
     // as the style overrides may also have affected the visible symbols
-    updateFilterByMap();
+    updateFilterByMap( false );
   }
   else
   {
@@ -619,14 +619,17 @@ void QgsComposerLegend::mapLayerStyleOverridesChanged()
   updateItem();
 }
 
-void QgsComposerLegend::updateFilterByMap()
+void QgsComposerLegend::updateFilterByMap( bool redraw )
 {
   if ( isRemoved() )
     return;
   // ask for update
   // the actual update will take place before the redraw.
   // This is to avoid multiple calls to the filter
   mFilterAskedForUpdate = true;
+
+  if ( redraw )
+    QgsComposerItem::updateItem();
 }
 
 void QgsComposerLegend::doUpdateFilterByMap()

src/core/composer/qgscomposerlegend.h

@@ -255,7 +255,7 @@ class CORE_EXPORT QgsComposerLegend : public QgsComposerItem
     void invalidateCurrentMap();
 
   private slots:
-    void updateFilterByMap();
+    void updateFilterByMap( bool redraw = true );
 
     //! update legend in case style of associated map has changed
     void mapLayerStyleOverridesChanged();