#12203 Improve selection of curves

Interpolate distance from mouse cursor to the line between index above and below closest index. This will make sure selection works when zoomed, and clear highlighting if mouse click is far from curves.

ApplicationLibCode/UserInterface/RiuQwtPlotWidget.cpp

@@ -875,28 +875,63 @@ QWidget* RiuQwtPlotWidget::getParentForOverlay() const
 //--------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
-void RiuQwtPlotWidget::findClosestPlotItem( const QPoint& pos, QwtPlotItem** closestItem, int* closestCurvePoint, double* distanceFromClick ) const
+void RiuQwtPlotWidget::findClosestPlotItem( const QPoint& pos, QwtPlotItem** closestItem, int* closestCurveSampleIndex, double* distanceFromClick ) const
 {
-    CAF_ASSERT( closestItem && closestCurvePoint && distanceFromClick );
+    CAF_ASSERT( closestItem && closestCurveSampleIndex && distanceFromClick );
 
-    // Force empty defaults
-    *closestItem       = nullptr;
-    *closestCurvePoint = -1;
-    *distanceFromClick = std::numeric_limits<double>::infinity();
+    *closestItem             = nullptr;
+    *closestCurveSampleIndex = -1;
+    *distanceFromClick       = std::numeric_limits<double>::infinity();
 
     const QwtPlotItemList& itmList = m_plot->itemList();
     for ( auto it : itmList )
     {
         if ( it->rtti() == QwtPlotItem::Rtti_PlotCurve )
         {
-            auto*  candidateCurve = static_cast<QwtPlotCurve*>( it );
-            double dist           = std::numeric_limits<double>::infinity();
-            int    curvePoint     = candidateCurve->closestPoint( pos, &dist );
+            auto*  candidateCurve   = static_cast<QwtPlotCurve*>( it );
+            double dist             = std::numeric_limits<double>::infinity();
+            int    curveSampleIndex = candidateCurve->closestPoint( pos, &dist );
+
+            if ( curveSampleIndex != -1 )
+            {
+                // Use the sample index before and after to interpolate the closest point on the curve.
+                const auto firstIndex  = std::max( 0, curveSampleIndex - 1 );
+                const auto secondIndex = std::min( curveSampleIndex + 1, (int)candidateCurve->dataSize() - 1 );
+
+                if ( firstIndex != secondIndex )
+                {
+                    const QPointF p0 = candidateCurve->sample( firstIndex );
+                    const QPointF p1 = candidateCurve->sample( secondIndex );
+
+                    const QwtScaleMap xMap = candidateCurve->plot()->canvasMap( candidateCurve->xAxis() );
+                    const QwtScaleMap yMap = candidateCurve->plot()->canvasMap( candidateCurve->yAxis() );
+
+                    const auto x0 = xMap.transform( p0.x() );
+                    const auto y0 = yMap.transform( p0.y() );
+                    const auto x1 = xMap.transform( p1.x() );
+                    const auto y1 = yMap.transform( p1.y() );
+
+                    const double dx = x1 - x0;
+                    const double dy = y1 - y0;
+                    const double d  = dx * dx + dy * dy;
+                    if ( d > 0.0 )
+                    {
+                        const double t = ( ( pos.x() - x0 ) * dx + ( pos.y() - y0 ) * dy ) / d;
+                        if ( t >= 0.0 && t <= 1.0 )
+                        {
+                            const double cx = x0 + t * dx - pos.x();
+                            const double cy = y0 + t * dy - pos.y();
+                            dist            = std::sqrt( cx * cx + cy * cy );
+                        }
+                    }
+                }
+            }
+
             if ( dist < *distanceFromClick )
             {
-                *closestItem       = candidateCurve;
-                *distanceFromClick = dist;
-                *closestCurvePoint = curvePoint;
+                *closestItem             = candidateCurve;
+                *distanceFromClick       = dist;
+                *closestCurveSampleIndex = curveSampleIndex;
             }
         }
         else if ( it->rtti() == QwtPlotItem::Rtti_PlotShape )
@@ -921,9 +956,9 @@ void RiuQwtPlotWidget::findClosestPlotItem( const QPoint& pos, QwtPlotItem** clo
                 double  dist        = horizontal ? std::abs( samplePoint.x() - scalePos.y() ) : std::abs( samplePoint.x() - scalePos.x() );
                 if ( dist < *distanceFromClick )
                 {
-                    *closestItem       = it;
-                    *closestCurvePoint = (int)i;
-                    *distanceFromClick = dist;
+                    *closestItem             = it;
+                    *closestCurveSampleIndex = (int)i;
+                    *distanceFromClick       = dist;
                 }
             }
         }
@@ -983,7 +1018,13 @@ void RiuQwtPlotWidget::selectClosestPlotItem( const QPoint& pos, bool toggleItem
             }
         }
 
-        if ( !wasToggledOff && clickedCurve ) curvesToSelect.push_back( clickedCurve );
+        if ( !wasToggledOff && clickedCurve )
+        {
+            if ( distanceFromClick < 100 )
+            {
+                curvesToSelect.push_back( clickedCurve );
+            }
+        }
 
         bool updateCurveOrder = false;
         resetPlotItemHighlighting( updateCurveOrder );

ApplicationLibCode/UserInterface/RiuQwtPlotWidget.h

@@ -154,8 +154,6 @@ public:
 
     void detachItems( RiuPlotWidget::PlotItemType plotItemType ) override;
 
-    void findClosestPlotItem( const QPoint& pos, QwtPlotItem** closestItem, int* closestCurvePoint, double* distanceFromClick ) const;
-
     const QColor& backgroundColor() const override;
 
     QWidget* getParentForOverlay() const override;
@@ -205,7 +203,9 @@ protected:
     virtual void onMouseMoveEvent( QMouseEvent* event );
 
 private:
-    void       selectClosestPlotItem( const QPoint& pos, bool toggleItemInSelection = false );
+    void selectClosestPlotItem( const QPoint& pos, bool toggleItemInSelection = false );
+    void findClosestPlotItem( const QPoint& pos, QwtPlotItem** closestItem, int* closestCurveSampleIndex, double* distanceFromClick ) const;
+
     static int defaultMinimumWidth();
 
     void highlightPlotAxes( QwtAxisId axisIdX, QwtAxisId axisIdY );