Don't wastefully recalculate memory provider extent after every

nyalldawson · nyalldawson · commit ebfa9f1479fb · 2017-06-12T10:19:21.000+10:00
feature addition Previously, the memory provider would automatically recalculate the extent of the layer after new features are added by looping through the entire set of existing features and calculating the bounding boxes. This is very wasteful, as many code paths add features one-by-one, so with every new feature added to the provider every existing feature is iterated over. This caused memory layers to slow to a crawl after many features are added. This commit improves the logic so that IF an existing layer extent is known, then it's updated on the fly as each individual feauture is added. Instead of looping through all features, we just expand the existing known extent with the added features bounds. If the extent isn't known, we just invalidate it when adding/deleting/modifying features, and defer the actual extent calculation until it's next requested. Makes memory layers many thousands of magnitudes of orders faster when adding lots of features (e.g. when memory providers are used as temporary outputs in processing) (cherry-picked from 6a87889)
diff --git a/src/providers/memory/qgsmemoryprovider.cpp b/src/providers/memory/qgsmemoryprovider.cpp
@@ -285,6 +285,16 @@ QgsFeatureIterator QgsMemoryProvider::getFeatures( const QgsFeatureRequest& requ
 
 QgsRectangle QgsMemoryProvider::extent()
 {
+  if ( mExtent.isEmpty() && !mFeatures.isEmpty() )
+  {
+    mExtent.setMinimal();
+    Q_FOREACH ( const QgsFeature &feat, mFeatures )
+    {
+      if ( feat.constGeometry() )
+        mExtent.unionRect( feat.constGeometry()->boundingBox() );
+    }
+  }
+
   return mExtent;
 }
 
@@ -328,6 +338,9 @@ QgsCoordinateReferenceSystem QgsMemoryProvider::crs()
 
 bool QgsMemoryProvider::addFeatures( QgsFeatureList & flist )
 {
+  // whether or not to update the layer extent on the fly as we add features
+  bool updateExtent = mFeatures.isEmpty() || !mExtent.isEmpty();
+
   // TODO: sanity checks of fields and geometries
   for ( QgsFeatureList::iterator it = flist.begin(); it != flist.end(); ++it )
   {
@@ -336,15 +349,19 @@ bool QgsMemoryProvider::addFeatures( QgsFeatureList & flist )
 
     mFeatures.insert( mNextFeatureId, *it );
 
-    // update spatial index
-    if ( mSpatialIndex )
-      mSpatialIndex->insertFeature( *it );
+    if ( it->constGeometry() )
+    {
+      if ( updateExtent )
+        mExtent.combineExtentWith( it->constGeometry()->boundingBox() );
+
+      // update spatial index
+      if ( mSpatialIndex )
+        mSpatialIndex->insertFeature( *it );
+    }
 
     mNextFeatureId++;
   }
 
-  updateExtent();
-
   return true;
 }
 
@@ -365,7 +382,7 @@ bool QgsMemoryProvider::deleteFeatures( const QgsFeatureIds & id )
     mFeatures.erase( fit );
   }
 
-  updateExtent();
+  updateExtents();
 
   return true;
 }
@@ -482,7 +499,7 @@ bool QgsMemoryProvider::changeGeometryValues( const QgsGeometryMap &geometry_map
       mSpatialIndex->insertFeature( *fit );
   }
 
-  updateExtent();
+  updateExtents();
 
   return true;
 }
@@ -533,21 +550,9 @@ int QgsMemoryProvider::capabilities() const
 }
 
 
-void QgsMemoryProvider::updateExtent()
+void QgsMemoryProvider::updateExtents()
 {
-  if ( mFeatures.isEmpty() )
-  {
-    mExtent = QgsRectangle();
-  }
-  else
-  {
-    mExtent.setMinimal();
-    Q_FOREACH ( const QgsFeature& feat, mFeatures )
-    {
-      if ( feat.constGeometry() )
-        mExtent.unionRect( feat.constGeometry()->boundingBox() );
-    }
-  }
+  mExtent.setMinimal();
 }
 
 
diff --git a/src/providers/memory/qgsmemoryprovider.h b/src/providers/memory/qgsmemoryprovider.h
@@ -158,10 +158,7 @@ class QgsMemoryProvider : public QgsVectorDataProvider
 
     virtual QgsCoordinateReferenceSystem crs() override;
 
-  protected:
-
-    // called when added / removed features or geometries has been changed
-    void updateExtent();
+    void updateExtents() override;
 
   private:
     // Coordinate reference system
@@ -170,7 +167,7 @@ class QgsMemoryProvider : public QgsVectorDataProvider
     // fields
     QgsFields mFields;
     QGis::WkbType mWkbType;
-    QgsRectangle mExtent;
+    mutable QgsRectangle mExtent;
 
     // features
     QgsFeatureMap mFeatures;
