statistics: convert box-and-whiskers plot to QSG

This is lazy: Derive from the bar chart item and add whiskers
in the subclassed render() function. The code is ugly, because
the base class function clears the dirty flags and therefore
the derived class has to remember them. Oh well.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

stats/boxseries.cpp

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "boxseries.h"
 #include "informationbox.h"
+#include "statsaxis.h"
 #include "statscolors.h"
 #include "statshelper.h"
 #include "statstranslations.h"
@@ -11,7 +12,7 @@
 
 // Constants that control the bar layout
 static const double boxWidth = 0.8; // 1.0 = full width of category
-static const int boxBorderWidth = 2;
+static const int boxBorderWidth = 2.0;
 
 BoxSeries::BoxSeries(QGraphicsScene *scene, StatsView &view, StatsAxis *xAxis, StatsAxis *yAxis,
 		     const QString &variable, const QString &unit, int decimals) :
@@ -24,23 +25,12 @@ BoxSeries::~BoxSeries()
 {
 }
 
-BoxSeries::Item::Item(QGraphicsScene *scene, BoxSeries *series, double lowerBound, double upperBound,
+BoxSeries::Item::Item(StatsView &view, BoxSeries *series, double lowerBound, double upperBound,
 		      const StatsQuartiles &q, const QString &binName) :
 	lowerBound(lowerBound), upperBound(upperBound), q(q),
 	binName(binName)
 {
-	box.setZValue(ZValues::series);
-	topWhisker.setZValue(ZValues::series);
-	bottomWhisker.setZValue(ZValues::series);
-	topBar.setZValue(ZValues::series);
-	bottomBar.setZValue(ZValues::series);
-	center.setZValue(ZValues::series);
-	scene->addItem(&box);
-	scene->addItem(&topWhisker);
-	scene->addItem(&bottomWhisker);
-	scene->addItem(&topBar);
-	scene->addItem(&bottomBar);
-	scene->addItem(&center);
+	item = view.createChartItem<ChartBoxItem>(ChartZValue::Series, boxBorderWidth);
 	highlight(false);
 	updatePosition(series);
 }
@@ -51,48 +41,34 @@ BoxSeries::Item::~Item()
 
 void BoxSeries::Item::highlight(bool highlight)
 {
-	QBrush brush = highlight ? QBrush(highlightedColor) : QBrush(fillColor);
-	QPen pen = highlight ? QPen(highlightedBorderColor, boxBorderWidth) : QPen(::borderColor, boxBorderWidth);
-	box.setBrush(brush);
-	box.setPen(pen);
-	topWhisker.setPen(pen);
-	bottomWhisker.setPen(pen);
-	topBar.setPen(pen);
-	bottomBar.setPen(pen);
-	center.setPen(pen);
+	if (highlight)
+		item->setColor(highlightedColor, highlightedBorderColor);
+	else
+		item->setColor(fillColor, ::borderColor);
 }
 
 void BoxSeries::Item::updatePosition(BoxSeries *series)
 {
+	StatsAxis *xAxis = series->xAxis;
+	StatsAxis *yAxis = series->yAxis;
+	if (!xAxis || !yAxis)
+		return;
+
 	double delta = (upperBound - lowerBound) * boxWidth;
 	double from = (lowerBound + upperBound - delta) / 2.0;
 	double to = (lowerBound + upperBound + delta) / 2.0;
-	double mid = (from + to) / 2.0;
 
-	QPointF topLeft, bottomRight;
-	QMarginsF margins(boxBorderWidth / 2.0, boxBorderWidth / 2.0, boxBorderWidth / 2.0, boxBorderWidth / 2.0);
-	topLeft = series->toScreen(QPointF(from, q.max));
-	bottomRight = series->toScreen(QPointF(to, q.min));
-	bounding = QRectF(topLeft, bottomRight).marginsAdded(margins);
-	double left = topLeft.x();
-	double right = bottomRight.x();
-	double width = right - left;
-	double top = topLeft.y();
-	double bottom = bottomRight.y();
-	QPointF q1 = series->toScreen(QPointF(mid, q.q1));
-	QPointF q2 = series->toScreen(QPointF(mid, q.q2));
-	QPointF q3 = series->toScreen(QPointF(mid, q.q3));
-	box.setRect(left, q3.y(), width, q1.y() - q3.y());
-	topWhisker.setLine(q3.x(), top, q3.x(), q3.y());
-	bottomWhisker.setLine(q1.x(), q1.y(), q1.x(), bottom);
-	topBar.setLine(left, top, right, top);
-	bottomBar.setLine(left, bottom, right, bottom);
-	center.setLine(left, q2.y(), right, q2.y());
+	double fromScreen = xAxis->toScreen(from);
+	double toScreen = xAxis->toScreen(to);
+	double q1 = yAxis->toScreen(q.q1);
+	double q3 = yAxis->toScreen(q.q3);
+	QRectF rect(fromScreen, q3, toScreen - fromScreen, q1 - q3);
+	item->setBox(rect, yAxis->toScreen(q.min), yAxis->toScreen(q.max), yAxis->toScreen(q.q2));
 }
 
 void BoxSeries::append(double lowerBound, double upperBound, const StatsQuartiles &q, const QString &binName)
 {
-	items.emplace_back(new Item(scene, this, lowerBound, upperBound, q, binName));
+	items.emplace_back(new Item(view, this, lowerBound, upperBound, q, binName));
 }
 
 void BoxSeries::updatePositions()
@@ -106,8 +82,8 @@ int BoxSeries::getItemUnderMouse(const QPointF &point)
 {
 	// Search the first item whose "end" position is greater than the cursor position.
 	auto it = std::lower_bound(items.begin(), items.end(), point.x(),
-			   [] (const std::unique_ptr<Item> &item, double x) { return item->bounding.right() < x; });
-	return it != items.end() && (*it)->bounding.contains(point) ? it - items.begin() : -1;
+			   [] (const std::unique_ptr<Item> &item, double x) { return item->item->getRect().right() < x; });
+	return it != items.end() && (*it)->item->getRect().contains(point) ? it - items.begin() : -1;
 }
 
 static QString infoItem(const QString &name, const QString &unit, int decimals, double value)

stats/boxseries.h

@@ -5,13 +5,12 @@
 #ifndef BOX_SERIES_H
 #define BOX_SERIES_H
 
+#include "chartitem.h"
 #include "statsseries.h"
 #include "statsvariables.h" // for StatsQuartiles
 
 #include <memory>
 #include <vector>
-#include <QGraphicsLineItem>
-#include <QGraphicsRectItem>
 
 struct InformationBox;
 class QGraphicsScene;
@@ -36,16 +35,12 @@ private:
 	int getItemUnderMouse(const QPointF &f);
 
 	struct Item {
-		QGraphicsRectItem box;
-		QGraphicsLineItem topWhisker, bottomWhisker;
-		QGraphicsLineItem topBar, bottomBar;
-		QGraphicsLineItem center;
-		QRectF bounding; // bounding box in screen coordinates
-		~Item();
+		std::unique_ptr<ChartBoxItem> item;
 		double lowerBound, upperBound;
 		StatsQuartiles q;
 		QString binName;
-		Item(QGraphicsScene *scene, BoxSeries *series, double lowerBound, double upperBound, const StatsQuartiles &q, const QString &binName);
+		Item(StatsView &view, BoxSeries *series, double lowerBound, double upperBound, const StatsQuartiles &q, const QString &binName);
+		~Item();
 		void updatePosition(BoxSeries *series);
 		void highlight(bool highlight);
 	};

stats/chartitem.cpp

@@ -279,3 +279,77 @@ QRectF ChartBarItem::getRect() const
 {
 	return rect;
 }
+
+ChartBoxItem::ChartBoxItem(StatsView &v, ChartZValue z, double borderWidth) :
+	ChartBarItem(v, z, borderWidth, false) // Only support for vertical boxes
+{
+}
+
+ChartBoxItem::~ChartBoxItem()
+{
+}
+
+void ChartBoxItem::render()
+{
+	// Remember old dirty values, since ChartBarItem::render() will clear them
+	bool oldPositionDirty = positionDirty;
+	bool oldColorDirty = colorDirty;
+	ChartBarItem::render();		// This will create the base node, so no need to check for that.
+	if (!whiskersNode) {
+		whiskersGeometry.reset(new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 10));
+		whiskersGeometry->setDrawingMode(QSGGeometry::DrawLines);
+		whiskersGeometry->setLineWidth(static_cast<float>(borderWidth));
+		whiskersMaterial.reset(new QSGFlatColorMaterial);
+		whiskersNode.reset(new QSGGeometryNode);
+		whiskersNode->setGeometry(whiskersGeometry.get());
+		whiskersNode->setMaterial(whiskersMaterial.get());
+
+		node->node->appendChildNode(whiskersNode.get());
+		// If this is the first time, make sure to update the geometry.
+		oldPositionDirty = oldColorDirty = true;
+	}
+
+	if (oldColorDirty) {
+		whiskersMaterial->setColor(borderColor);
+		whiskersNode->markDirty(QSGNode::DirtyMaterial);
+	}
+
+	if (oldPositionDirty) {
+		auto vertices = whiskersGeometry->vertexDataAsPoint2D();
+		double left = rect.left();
+		double right = rect.right();
+		double mid = (left + right) / 2.0;
+		// top bar
+		setPoint(vertices[0], QPointF(left, max));
+		setPoint(vertices[1], QPointF(right, max));
+		// top whisker
+		setPoint(vertices[2], QPointF(mid, max));
+		setPoint(vertices[3], QPointF(mid, rect.top()));
+		// bottom bar
+		setPoint(vertices[4], QPointF(left, min));
+		setPoint(vertices[5], QPointF(right, min));
+		// bottom whisker
+		setPoint(vertices[6], QPointF(mid, min));
+		setPoint(vertices[7], QPointF(mid, rect.bottom()));
+		// median indicator
+		setPoint(vertices[8], QPointF(left, median));
+		setPoint(vertices[9], QPointF(right, median));
+		whiskersNode->markDirty(QSGNode::DirtyGeometry);
+	}
+}
+
+void ChartBoxItem::setBox(const QRectF &rect, double minIn, double maxIn, double medianIn)
+{
+	min = minIn;
+	max = maxIn;
+	median = medianIn;
+	setRect(rect);
+}
+
+QRectF ChartBoxItem::getRect() const
+{
+	QRectF res = rect;
+	res.setTop(min);
+	res.setBottom(max);
+	return rect;
+}

stats/chartitem.h

@@ -123,7 +123,7 @@ public:
 	void setRect(const QRectF &rect);
 	QRectF getRect() const;
 	void render() override;		// Only call on render thread!
-private:
+protected:
 	QColor color, borderColor;
 	double borderWidth;
 	QRectF rect;
@@ -135,6 +135,22 @@ private:
 	std::unique_ptr<QSGGeometry> borderGeometry;
 };
 
+// A box-and-whiskers item. This is a bit lazy: derive from the bar item and add whiskers.
+class ChartBoxItem : public ChartBarItem {
+public:
+	ChartBoxItem(StatsView &v, ChartZValue z, double borderWidth);
+	~ChartBoxItem();
+	void setBox(const QRectF &rect, double min, double max, double median); // The rect describes Q1, Q3.
+	QRectF getRect() const;		// Note: this extends the center rectangle to include the whiskers.
+	void render() override;		// Only call on render thread!
+private:
+	double min, max, median;
+	std::unique_ptr<QSGGeometryNode> whiskersNode;
+	std::unique_ptr<QSGFlatColorMaterial> whiskersMaterial;
+	std::unique_ptr<QSGGeometry> whiskersGeometry;
+};
+
+
 // Implementation detail of templates - move to serparate header file
 template <typename Node>
 void HideableChartItem<Node>::setVisible(bool visibleIn)