try to smooth out curves

examples/iot-dashboard/Diagram.cpp

@@ -2,6 +2,83 @@
 
 #include <QPainter>
 
+#include <cmath>
+
+namespace
+{
+    float distance( const QPointF& pt1, const QPointF& pt2 )
+    {
+        float hd = ( pt1.x() - pt2.x() ) * ( pt1.x() - pt2.x() );
+        float vd = ( pt1.y() - pt2.y() ) * ( pt1.y() - pt2.y() );
+        return std::sqrt( hd + vd );
+    }
+
+    QPointF getLineStart( const QPointF& pt1, const QPointF& pt2 )
+    {
+        QPointF pt;
+        float rat = 10.0 / distance( pt1, pt2 );
+
+        if( rat > 0.5 )
+        {
+            rat = 0.5;
+        }
+
+        pt.setX( ( 1.0 - rat ) * pt1.x() + rat * pt2.x() );
+        pt.setY( ( 1.0 - rat ) * pt1.y() + rat * pt2.y() );
+        return pt;
+    }
+
+    QPointF getLineEnd( const QPointF& pt1, const QPointF& pt2 )
+    {
+        QPointF pt;
+        float rat = 10.0 / distance( pt1, pt2 );
+
+        if( rat > 0.5 )
+        {
+            rat = 0.5;
+        }
+
+        pt.setX( rat * pt1.x() + ( 1.0 - rat )*pt2.x() );
+        pt.setY( rat * pt1.y() + ( 1.0 - rat )*pt2.y() );
+        return pt;
+    }
+
+    QPainterPath smoothOut( const QPainterPath& path )
+    {
+        QList<QPointF> points;
+        QPointF p;
+
+        for( int i = 0; i < path.elementCount() - 1; i++ )
+        {
+            p = QPointF( path.elementAt( i ).x, path.elementAt( i ).y );
+            points.append( p );
+        }
+
+        QPointF pt1;
+        QPointF pt2;
+        QPainterPath newPath;
+
+        for( int i = 0; i < points.count() - 1; i++ )
+        {
+            pt1 = getLineStart( points[i], points[i + 1] );
+
+            if( i == 0 )
+            {
+                newPath.moveTo( points[0] );
+            }
+            else
+            {
+                newPath.quadTo( points[i], pt1 );
+            }
+
+            pt2 = getLineEnd( points[i], points[i + 1] );
+            newPath.lineTo( pt2 );
+        }
+
+        return newPath;
+    }
+}
+
 static constexpr int segments = 7;
 
 Diagram::Diagram( QQuickItem* parent )
@@ -23,32 +100,49 @@ DiagramContent::DiagramContent( QQuickItem* parent ) : QQuickPaintedItem( parent
 
 void DiagramContent::paint( QPainter* painter )
 {
-//    auto size = contentsSize();
-//    QRectF outerRect( {0, 0}, size );
-
     painter->setRenderHint( QPainter::Antialiasing, true );
 
-    qreal stepSize = width() / segments;
-
-    QLinearGradient myGradient( {width() / 2, 0}, {width() / 2, height()} );
-    myGradient.setColorAt( 0, "#996776FF" );
-    myGradient.setColorAt( 1, "#116776FF" );
-    QPen myPen( Qt::transparent );
-
-    QPainterPath myPath;
-    myPath.moveTo( 0, height() );
-
-    qreal ys[7] = {0.8, 0.85, 0.92, 0.5, 0.88, 0.7, 0.8};
-
-    for( int i = 0; i < stepSize; i++ )
+    QPair<QColor, QColor> colors[] =
     {
-        qreal x1 = i * stepSize + stepSize / 2;
-        qreal y = ys[i] * height();
-        qreal x2 = x1;
-        myPath.cubicTo( x1, y, x2, height() * ( 1 - ys[i] ), stepSize * ( i + 1 ), height() * ( 1 - ys[i] ) );
-    }
+        {"#996776FF", "#116776FF"},
+        {"#aaFF3122", "#11FF3122"},
+        {"#FF7D34", "#11FF7D34"}
+    };
 
-    painter->setBrush( myGradient );
-    painter->setPen( myPen );
-    painter->drawPath( myPath );
+    qreal yValues[][8] =
+    {
+        {0.8, 0.85, 0.92, 0.5, 0.88, 0.7, 0.8, 0.3},
+        {0.2, 0.6, 0.5, 0.9, 0.3, 0.4, 0.8, 0.4},
+        {0.5, 0.4, 0.7, 0.1, 0.6, 0.9, 0.3, 0.1}
+    };
+
+    for( int i = 0; i < 3; i++ )
+    {
+        QLinearGradient myGradient( {width() / 2, 0}, {width() / 2, height()} );
+        myGradient.setColorAt( 0, colors[i].first );
+        myGradient.setColorAt( 1, colors[i].second );
+        QPen myPen( Qt::transparent );
+
+        QPainterPath myPath;
+        myPath.moveTo( 0, height() );
+        myPath.lineTo( 0, 50 );
+
+        qreal stepSize = width() / segments;
+
+        for( int j = 1; j < segments; j++ )
+        {
+            qreal x1 = j * stepSize + stepSize / 2;
+            qreal y = ( 1 - yValues[i][j] ) * height();
+            myPath.lineTo( x1, y );
+        }
+
+        myPath.lineTo( width(), ( 1 - yValues[i][7] ) * height() );
+        myPath.lineTo( width(), height() );
+
+        QPainterPath smoothPath = smoothOut( myPath );
+        smoothPath.lineTo( width(), height() );
+        painter->setBrush( myGradient );
+        painter->setPen( myPen );
+        painter->drawPath( smoothPath );
+    }
 }