[Backport]: Avoid intersection for QgsMapToolAddPart. Fixes ticket #4624

Author: mhugent

src/app/qgsmaptooladdpart.cpp

@@ -125,6 +125,22 @@ void QgsMapToolAddPart::canvasReleaseEvent( QMouseEvent * e )
       {
         //close polygon
         closePolygon();
+        //avoid intersections
+        QgsGeometry* geom = QgsGeometry::fromPolygon( QgsPolygon() << points().toVector() );
+        if ( geom )
+        {
+          geom->avoidIntersections();
+          QgsPolygon poly = geom->asPolygon();
+          if ( poly.size() < 1 )
+          {
+            stopCapturing();
+            delete geom;
+            vlayer->destroyEditCommand();
+            return;
+          }
+          setPoints( geom->asPolygon()[0].toList() );
+          delete geom;
+        }
       }
 
       vlayer->beginEditCommand( tr( "Part added" ) );

src/app/qgsmaptoolcapture.h

@@ -91,6 +91,7 @@ class QgsMapToolCapture : public QgsMapToolEdit
     QList<QgsPoint>::iterator begin() { return mCaptureList.begin(); }
     QList<QgsPoint>::iterator end() { return mCaptureList.end(); }
     const QList<QgsPoint> &points() { return mCaptureList; }
+    void setPoints( const QList<QgsPoint>& pointList ) { mCaptureList = pointList; }
     void closePolygon();
 
   private: