Fix usability issues of tracing with offset

qgis · Oct 10, 2017 · f16b215 · f16b215
1 parent b140b29
commit f16b215
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Showing 3 changed files with 37 additions and 2 deletions.
diff --git a/src/core/qgstracer.cpp b/src/core/qgstracer.cpp
@@ -729,8 +729,10 @@ QVector<QgsPointXY> QgsTracer::findShortestPath( const QgsPointXY &p1, const Qgs
       // sometimes (with negative offset?) the resulting curve is reversed
       if ( points.count() >= 2 )
       {
-        double diff = points[0].distance( p1 );
-        if ( !qgsDoubleNear( diff, mOffset ) )
+        QgsPointXY res1 = points.first(), res2 = points.last();
+        double diffNormal = res1.distance( p1 ) + res2.distance( p2 );
+        double diffReversed = res1.distance( p2 ) + res2.distance( p1 );
+        if ( diffReversed < diffNormal )
           std::reverse( points.begin(), points.end() );
       }
     }

diff --git a/src/gui/qgsmaptoolcapture.cpp b/src/gui/qgsmaptoolcapture.cpp
@@ -142,6 +142,12 @@ QgsPointXY QgsMapToolCapture::tracingStartPoint()
     QgsMapLayer *layer = mCanvas->currentLayer();
     if ( !layer )
       return QgsPointXY();
+
+    // if we have starting point from previous trace, then preferably use that one
+    // (useful when tracing with offset)
+    if ( mTracingStartPoint != QgsPointXY() )
+      return mTracingStartPoint;
+
     QgsPoint v = mCaptureCurve.endPoint();
     return toMapCoordinates( layer, QgsPointXY( v.x(), v.y() ) );
   }
@@ -179,6 +185,15 @@ bool QgsMapToolCapture::tracingMouseMove( QgsMapMouseEvent *e )
   if ( mCaptureMode == CapturePolygon )
     mTempRubberBand->addPoint( *mRubberBand->getPoint( 0, 0 ), false );
 
+  // if there is offset, we need to add the previous point as well otherwise there may be a gap
+  // between the existing rubber band and temporary rubber band
+  if ( mRubberBand->numberOfVertices() != 0 )
+  {
+    QgsPointXY lastPoint = *mRubberBand->getPoint( 0, mRubberBand->numberOfVertices() - 1 );
+    if ( points[0] != lastPoint )
+      mTempRubberBand->addPoint( lastPoint, false );
+  }
+
   //  update rubberband
   for ( int i = 0; i < points.count(); ++i )
     mTempRubberBand->addPoint( points.at( i ), i == points.count() - 1 );
@@ -237,7 +252,11 @@ bool QgsMapToolCapture::tracingAddVertex( const QgsPointXY &point )
     QgsVertexId::VertexType type;
     mCaptureCurve.pointAt( mCaptureCurve.numPoints() - 1, last, type );
     if ( last != lp )
+    {
+      // last captured point and first point of the trace are not the same (different offset maybe)
+      // so we need to use also the first point of the trace
       indexStart = 0;
+    }
   }
 
   // transform points
@@ -434,6 +453,10 @@ int QgsMapToolCapture::addVertex( const QgsPointXY &point, const QgsPointLocator
     traceCreated = tracingAddVertex( point );
   }
 
+  // keep new tracing start point if we created a trace. This is useful when tracing with
+  // offset so that the user stays "snapped"
+  mTracingStartPoint = traceCreated ? point : QgsPointXY();
+
   if ( !traceCreated )
   {
     // ordinary digitizing
@@ -514,6 +537,8 @@ QList<QgsPointLocator::Match> QgsMapToolCapture::snappingMatches() const
 
 void QgsMapToolCapture::undo()
 {
+  mTracingStartPoint = QgsPointXY();
+
   if ( mRubberBand )
   {
     int rubberBandSize = mRubberBand->numberOfVertices();
@@ -600,6 +625,8 @@ void QgsMapToolCapture::stopCapturing()
 
   mGeomErrors.clear();
 
+  mTracingStartPoint = QgsPointXY();
+
 #ifdef Q_OS_WIN
   Q_FOREACH ( QWidget *w, qApp->topLevelWidgets() )
   {

diff --git a/src/gui/qgsmaptoolcapture.h b/src/gui/qgsmaptoolcapture.h
@@ -240,6 +240,12 @@ class GUI_EXPORT QgsMapToolCapture : public QgsMapToolAdvancedDigitizing
 
     QgsVertexMarker *mSnappingMarker = nullptr;
 
+    //! Keeps point (in map units) snapped to a segment where we most recently finished tracing,
+    //! so that we can use as the starting point for further tracing. This is useful mainly when
+    //! tracing with offset: without knowledge of this point user would need to click a segment
+    //! again after every time a new trace with offset is created (to get new "anchor" point)
+    QgsPointXY mTracingStartPoint;
+
 #ifdef Q_OS_WIN
     int mSkipNextContextMenuEvent;
 #endif