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, 85 insertions, 87 deletions

diff --git a/stats/statsview.cpp b/stats/statsview.cpp
index f42296fc2..1533583ba 100644
--- a/stats/statsview.cpp
+++ b/stats/statsview.cpp
@@ -6,7 +6,9 @@
 #include "pieseries.h"
 #include "scatterseries.h"
 #include "statsaxis.h"
+#include "statscolors.h"
 #include "statsgrid.h"
+#include "statshelper.h"
 #include "statsstate.h"
 #include "statstranslations.h"
 #include "statsvariables.h"
@@ -15,12 +17,35 @@
 #include "core/subsurface-qt/divelistnotifier.h"
 
 #include <cmath>
-#include <QQuickItem>
-#include <QAbstractSeries>
-#include <QChart>
+#include <QGraphicsScene>
 #include <QGraphicsSceneHoverEvent>
 #include <QGraphicsSimpleTextItem>
-#include <QLocale>
+#include <QQuickItem>
+#include <QQuickWindow>
+#include <QSGImageNode>
+#include <QSGTexture>
+
+QSGNode *StatsView::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *)
+{
+	// The QtQuick drawing interface is utterly bizzare with a distinct 1980ies-style memory management.
+	// This is just a copy of what is found in Qt's documentation.
+	QSGImageNode *n = static_cast<QSGImageNode *>(oldNode);
+	if (!n)
+		n = window()->createImageNode();
+
+	QRectF rect = boundingRect();
+	if (plotRect != rect) {
+		plotRect = rect;
+		plotAreaChanged(plotRect.size());
+	}
+
+	img->fill(backgroundColor);
+	scene.render(painter.get());
+	texture.reset(window()->createTextureFromImage(*img, QQuickWindow::TextureIsOpaque));
+	n->setTexture(texture.get());
+	n->setRect(rect);
+	return n;
+}
 
 // Constants that control the graph layouts
 static const QColor quartileMarkerColor(Qt::red);
@@ -28,76 +53,45 @@ static const double quartileMarkerSize = 15.0;
 static const double sceneBorder = 5.0;			// Border between scene edges and statitistics view
 static const double titleBorder = 2.0;			// Border between title and chart
 
-static const QUrl urlStatsView = QUrl(QStringLiteral("qrc:/qml/statsview.qml"));
-
-// We use QtQuick's ChartView so that we can show the statistics on mobile.
-// However, accessing the ChartView from C++ is maliciously cumbersome and
-// the full QChart interface is not exported. Fortunately, the interface
-// leaks the QChart object: We can create a dummy-series and access the chart
-// object via the chart() accessor function. By creating a "PieSeries", the
-// ChartView does not automatically add axes.
-static QtCharts::QChart *getChart(QQuickItem *item)
-{
-	QtCharts::QAbstractSeries *abstract_series;
-	if (!item)
-		return nullptr;
-	if (!QMetaObject::invokeMethod(item, "createSeries", Qt::AutoConnection,
-				       Q_RETURN_ARG(QtCharts::QAbstractSeries *, abstract_series),
-				       Q_ARG(int, QtCharts::QAbstractSeries::SeriesTypePie),
-				       Q_ARG(QString, QString()))) {
-		qWarning("Couldn't call createSeries()");
-		return nullptr;
-	}
-	QtCharts::QChart *res = abstract_series->chart();
-	res->removeSeries(abstract_series);
-	delete abstract_series;
-	return res;
-}
-
-bool StatsView::EventFilter::eventFilter(QObject *o, QEvent *event)
-{
-	if (event->type() == QEvent::GraphicsSceneHoverMove) {
-		QGraphicsSceneHoverEvent *hover = static_cast<QGraphicsSceneHoverEvent *>(event);
-		view->hover(hover->pos());
-		return true;
-	}
-	return QObject::eventFilter(o, event);
-}
-
-StatsView::StatsView(QWidget *parent) : QQuickWidget(parent),
+StatsView::StatsView(QQuickItem *parent) : QQuickItem(parent),
 	highlightedSeries(nullptr),
 	xAxis(nullptr),
-	yAxis(nullptr),
-	eventFilter(this)
+	yAxis(nullptr)
 {
-	setResizeMode(QQuickWidget::SizeRootObjectToView);
-	// if we get a failure to load the QML file (e.g., when the QtCharts QML modules aren't found)
-	// the chart will be null
-	setSource(urlStatsView);
-	chart = getChart(rootObject());
-	if (chart) {
-		connect(chart, &QtCharts::QChart::plotAreaChanged, this, &StatsView::plotAreaChanged);
-		connect(&diveListNotifier, &DiveListNotifier::numShownChanged, this, &StatsView::replotIfVisible);
-
-		chart->installEventFilter(&eventFilter);
-		chart->setAcceptHoverEvents(true);
-		chart->legend()->setVisible(false);
-	}
+	setFlag(ItemHasContents, true);
+
+	connect(&diveListNotifier, &DiveListNotifier::numShownChanged, this, &StatsView::replotIfVisible);
+
+	setAcceptHoverEvents(true);
 
 	QFont font;
 	titleFont = QFont(font.family(), font.pointSize(), QFont::Light);	// Make configurable
 }
 
+StatsView::StatsView() : StatsView(nullptr)
+{
+}
+
 StatsView::~StatsView()
 {
 }
 
-void StatsView::plotAreaChanged(const QRectF &r)
+void StatsView::plotAreaChanged(const QSizeF &s)
 {
-	double left = r.x() + sceneBorder;
-	double top = r.y() + sceneBorder;
-	double right = r.right() - sceneBorder;
-	double bottom = r.bottom() - sceneBorder;
+	// Make sure that image is at least one pixel wide / high, otherwise
+	// the painter starts acting up.
+	int w = std::max(1, static_cast<int>(floor(s.width())));
+	int h = std::max(1, static_cast<int>(floor(s.height())));
+	scene.setSceneRect(QRectF(0, 0, static_cast<double>(w), static_cast<double>(h)));
+	painter.reset();
+	img.reset(new QImage(w, h, QImage::Format_RGB32));
+	painter.reset(new QPainter(img.get()));
+	painter->setRenderHint(QPainter::Antialiasing);
+
+	double left = sceneBorder;
+	double top = sceneBorder;
+	double right = s.width() - sceneBorder;
+	double bottom = s.height() - sceneBorder;
 	const double minSize = 30.0;
 
 	if (title)
@@ -140,8 +134,13 @@ void StatsView::replotIfVisible()
 		plot(state);
 }
 
-void StatsView::hover(QPointF pos)
+void StatsView::hoverEnterEvent(QHoverEvent *)
 {
+}
+
+void StatsView::hoverMoveEvent(QHoverEvent *event)
+{
+	QPointF pos(event->pos());
 	for (auto &series: series) {
 		if (series->hover(pos)) {
 			if (series.get() != highlightedSeries) {
@@ -149,7 +148,7 @@ void StatsView::hover(QPointF pos)
 					highlightedSeries->unhighlight();
 				highlightedSeries = series.get();
 			}
-			return;
+			return update();
 		}
 	}
 
@@ -157,13 +156,14 @@ void StatsView::hover(QPointF pos)
 	if (highlightedSeries) {
 		highlightedSeries->unhighlight();
 		highlightedSeries = nullptr;
+		update();
 	}
 }
 
 template <typename T, class... Args>
 T *StatsView::createSeries(Args&&... args)
 {
-	T *res = new T(chart, xAxis, yAxis, std::forward<Args>(args)...);
+	T *res = new T(&scene, xAxis, yAxis, std::forward<Args>(args)...);
 	series.emplace_back(res);
 	series.back()->updatePositions();
 	return res;
@@ -175,7 +175,7 @@ void StatsView::setTitle(const QString &s)
 		title.reset();
 		return;
 	}
-	title = std::make_unique<QGraphicsSimpleTextItem>(s, chart);
+	title = createItemPtr<QGraphicsSimpleTextItem>(&scene, s);
 	title->setFont(titleFont);
 }
 
@@ -183,7 +183,7 @@ void StatsView::updateTitlePos()
 {
 	if (!title)
 		return;
-	QRectF rect = chart->plotArea();
+	QRectF rect = scene.sceneRect();
 	title->setPos(sceneBorder + (rect.width() - title->boundingRect().width()) / 2.0,
 		      sceneBorder);
 }
@@ -191,7 +191,7 @@ void StatsView::updateTitlePos()
 template <typename T, class... Args>
 T *StatsView::createAxis(const QString &title, Args&&... args)
 {
-	T *res = new T(chart, title, std::forward<Args>(args)...);
+	T *res = createItem<T>(&scene, title, std::forward<Args>(args)...);
 	axes.emplace_back(res);
 	return res;
 }
@@ -201,13 +201,11 @@ void StatsView::setAxes(StatsAxis *x, StatsAxis *y)
 	xAxis = x;
 	yAxis = y;
 	if (x && y)
-		grid = std::make_unique<StatsGrid>(chart, *x, *y);
+		grid = std::make_unique<StatsGrid>(&scene, *x, *y);
 }
 
 void StatsView::reset()
 {
-	if (!chart)
-		return;
 	highlightedSeries = nullptr;
 	xAxis = yAxis = nullptr;
 	legend.reset();
@@ -215,7 +213,6 @@ void StatsView::reset()
 	quartileMarkers.clear();
 	regressionLines.clear();
 	histogramMarkers.clear();
-	chart->removeAllSeries();
 	grid.reset();
 	axes.clear();
 	title.reset();
@@ -225,12 +222,13 @@ void StatsView::plot(const StatsState &stateIn)
 {
 	state = stateIn;
 	plotChart();
-	plotAreaChanged(chart->plotArea());
+	plotAreaChanged(scene.sceneRect().size());
+	update();
 }
 
 void StatsView::plotChart()
 {
-	if (!chart || !state.var1)
+	if (!state.var1)
 		return;
 	reset();
 
@@ -402,7 +400,7 @@ void StatsView::plotBarChart(const std::vector<dive *> &dives,
 
 	// Paint legend first, because the bin-names will be moved away from.
 	if (showLegend)
-		legend = std::make_unique<Legend>(chart, data.vbinNames);
+		legend = createItemPtr<Legend>(&scene, data.vbinNames);
 
 	std::vector<BarSeries::MultiItem> items;
 	items.reserve(data.hbin_counts.size());
@@ -619,7 +617,7 @@ void StatsView::plotPieChart(const std::vector<dive *> &dives,
 	PieSeries *series = createSeries<PieSeries>(categoryVariable->name(), data, keepOrder, labels);
 
 	if (showLegend)
-		legend = std::make_unique<Legend>(chart, series->binNames());
+		legend = createItemPtr<Legend>(&scene, series->binNames());
 }
 
 void StatsView::plotDiscreteBoxChart(const std::vector<dive *> &dives,
@@ -689,17 +687,17 @@ void StatsView::plotDiscreteScatter(const std::vector<dive *> &dives,
 		if (quartiles) {
 			StatsQuartiles quartiles = StatsVariable::quartiles(array);
 			if (quartiles.isValid()) {
-				quartileMarkers.emplace_back(x, quartiles.q1, chart, catAxis, valAxis);
-				quartileMarkers.emplace_back(x, quartiles.q2, chart, catAxis, valAxis);
-				quartileMarkers.emplace_back(x, quartiles.q3, chart, catAxis, valAxis);
+				quartileMarkers.emplace_back(x, quartiles.q1, &scene, catAxis, valAxis);
+				quartileMarkers.emplace_back(x, quartiles.q2, &scene, catAxis, valAxis);
+				quartileMarkers.emplace_back(x, quartiles.q3, &scene, catAxis, valAxis);
 			}
 		}
 		x += 1.0;
 	}
 }
 
-StatsView::QuartileMarker::QuartileMarker(double pos, double value, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
-	item(new QGraphicsLineItem(chart)),
+StatsView::QuartileMarker::QuartileMarker(double pos, double value, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) :
+	item(createItemPtr<QGraphicsLineItem>(scene)),
 	xAxis(xAxis), yAxis(yAxis),
 	pos(pos),
 	value(value)
@@ -719,8 +717,8 @@ void StatsView::QuartileMarker::updatePosition()
 		      x + quartileMarkerSize / 2.0, y);
 }
 
-StatsView::RegressionLine::RegressionLine(double a, double b, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
-	item(new QGraphicsLineItem(chart)),
+StatsView::RegressionLine::RegressionLine(double a, double b, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) :
+	item(createItemPtr<QGraphicsLineItem>(scene)),
 	xAxis(xAxis), yAxis(yAxis),
 	a(a), b(b)
 {
@@ -751,8 +749,8 @@ void StatsView::RegressionLine::updatePosition()
 		      xAxis->toScreen(maxX), yAxis->toScreen(a * maxX + b));
 }
 
-StatsView::HistogramMarker::HistogramMarker(double val, bool horizontal, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
-	item(new QGraphicsLineItem(chart)),
+StatsView::HistogramMarker::HistogramMarker(double val, bool horizontal, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) :
+	item(createItemPtr<QGraphicsLineItem>(scene)),
 	xAxis(xAxis), yAxis(yAxis),
 	val(val), horizontal(horizontal)
 {
@@ -777,12 +775,12 @@ void StatsView::HistogramMarker::updatePosition()
 
 void StatsView::addHistogramMarker(double pos, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis)
 {
-	histogramMarkers.emplace_back(pos, isHorizontal, pen, chart, xAxis, yAxis);
+	histogramMarkers.emplace_back(pos, isHorizontal, pen, &scene, xAxis, yAxis);
 }
 
 void StatsView::addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis)
 {
-	regressionLines.emplace_back(a, b, QPen(Qt::red), chart, xAxis, yAxis);
+	regressionLines.emplace_back(a, b, QPen(Qt::red), &scene, xAxis, yAxis);
 }
 
 // Yikes, we get our data in different kinds of (bin, value) pairs.
@@ -942,7 +940,7 @@ void StatsView::plotHistogramStackedChart(const std::vector<dive *> &dives,
 
 	BarPlotData data(categoryBins, *valueBinner);
 	if (showLegend)
-		legend = std::make_unique<Legend>(chart, data.vbinNames);
+		legend = createItemPtr<Legend>(&scene, data.vbinNames);
 
 	CountAxis *valAxis = createCountAxis(data.maxCategoryCount, isHorizontal);