statistics: convert chart to QQuickItem

It turns out that the wrong base class was used for the chart.
QQuickWidget can only be used on desktop, not in a mobile UI.

Therefore, turn this into a QQuickItem and move the container
QQuickWidget into desktop-only code.

Currently, this code is insane: The chart is rendered onto a
QGraphicsScene (as it was before), which is then rendered into
a QImage, which is transformed into a QSGTexture, which is then
projected onto the device. This is performed on every mouse
move event, since these events in general change the position
of the info-box.

The plan is to slowly convert elements such as the info-box into
QQuickItems. Browsing the QtQuick documentation, this will
not be much fun.

Also note that the rendering currently tears, flickers and has
antialiasing artifacts, most likely owing to integer (QImage)
to floating point (QGraphicsScene, QQuickItem) conversion
problems. The data flow is
QGraphicsScene (float) -> QImage (int) -> QQuickItem (float).

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

1 files changed, 22 insertions, 23 deletions

diff --git a/stats/statsview.h b/stats/statsview.h
index fd8ec1e2c..fbf51d46e 100644
--- a/stats/statsview.h
+++ b/stats/statsview.h
@@ -5,7 +5,10 @@
 #include "statsstate.h"
 #include <memory>
 #include <QFont>
-#include <QQuickWidget>
+#include <QGraphicsScene>
+#include <QImage>
+#include <QPainter>
+#include <QQuickItem>
 
 struct dive;
 struct StatsBinner;
@@ -13,10 +16,6 @@ struct StatsBin;
 struct StatsState;
 struct StatsVariable;
 
-namespace QtCharts {
-	class QAbstractSeries;
-	class QChart;
-}
 class QGraphicsLineItem;
 class QGraphicsSimpleTextItem;
 class StatsSeries;
@@ -26,21 +25,31 @@ class HistogramAxis;
 class StatsAxis;
 class StatsGrid;
 class Legend;
+class QSGTexture;
 
 enum class ChartSubType : int;
 enum class StatsOperation : int;
 
-class StatsView : public QQuickWidget {
+class StatsView : public QQuickItem {
 	Q_OBJECT
 public:
-	StatsView(QWidget *parent = NULL);
+	StatsView();
+	StatsView(QQuickItem *parent);
 	~StatsView();
 
 	void plot(const StatsState &state);
 private slots:
-	void plotAreaChanged(const QRectF &plotArea);
 	void replotIfVisible();
 private:
+	// QtQuick related things
+	QRectF plotRect;
+	QSGNode *updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *updatePaintNodeData) override;
+	std::unique_ptr<QImage> img;
+	std::unique_ptr<QPainter> painter;
+	QGraphicsScene scene;
+	std::unique_ptr<QSGTexture> texture;
+
+	void plotAreaChanged(const QSizeF &size);
 	void reset(); // clears all series and axes
 	void setAxes(StatsAxis *x, StatsAxis *y);
 	void plotBarChart(const std::vector<dive *> &dives,
@@ -102,7 +111,7 @@ private:
 		std::unique_ptr<QGraphicsLineItem> item;
 		StatsAxis *xAxis, *yAxis;
 		double pos, value;
-		QuartileMarker(double pos, double value, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
+		QuartileMarker(double pos, double value, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis);
 		void updatePosition();
 	};
 
@@ -112,7 +121,7 @@ private:
 		StatsAxis *xAxis, *yAxis;
 		double a, b;			// y = ax + b
 		void updatePosition();
-		RegressionLine(double a, double b, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
+		RegressionLine(double a, double b, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis);
 	};
 
 	// A line marking median or mean in histograms
@@ -122,14 +131,13 @@ private:
 		double val;
 		bool horizontal;
 		void updatePosition();
-		HistogramMarker(double val, bool horizontal, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
+		HistogramMarker(double val, bool horizontal, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis);
 	};
 
 	void addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis);
 	void addHistogramMarker(double pos, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis);
 
 	StatsState state;
-	QtCharts::QChart *chart;
 	QFont titleFont;
 	std::vector<std::unique_ptr<StatsAxis>> axes;
 	std::unique_ptr<StatsGrid> grid;
@@ -142,17 +150,8 @@ private:
 	StatsSeries *highlightedSeries;
 	StatsAxis *xAxis, *yAxis;
 
-	// This is unfortunate: we can't derive from QChart, because the chart is allocated by QML.
-	// Therefore, we have to listen to hover events using an events-filter.
-	// Probably we should try to get rid of the QML ChartView.
-	struct EventFilter : public QObject {
-		StatsView *view;
-		EventFilter(StatsView *view) : view(view) {}
-	private:
-		bool eventFilter(QObject *o, QEvent *event);
-	} eventFilter;
-	friend EventFilter;
-	void hover(QPointF pos);
+	void hoverEnterEvent(QHoverEvent *event) override;
+	void hoverMoveEvent(QHoverEvent *event) override;
 };
 
 #endif