statistics: turn axes into QSGNode

Render the labels and the title into a pixmap and render
the ticks and the base line using individual QSGNodes.
Attempting to render the ticks likewise into the pixmap
gave horrible results, because (quite obviously) rendering
with QPainter and the QSG shader gives non-matching ticks
and grid lines.

The memory management had to be changed a bit: The ChartItems
were collected in the root QSGNode. However, the axes are added
before the first plotting, so this node might not exist.
Therefore, store the axes in the StatsView object.

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

4 files changed, 143 insertions, 117 deletions

diff --git a/stats/statsaxis.cpp b/stats/statsaxis.cpp
index 2c5a5d961..5c4f0403e 100644
--- a/stats/statsaxis.cpp
+++ b/stats/statsaxis.cpp
@@ -4,6 +4,7 @@
 #include "statshelper.h"
 #include "statstranslations.h"
 #include "statsvariables.h"
+#include "statsview.h"
 #include "zvalues.h"
 #include "core/pref.h"
 #include "core/subsurface-time.h"
@@ -23,23 +24,19 @@ static const double axisLabelSpaceVertical = 2.0;	// Space between axis or ticks
 static const double axisTitleSpaceHorizontal = 2.0;	// Space between labels and title
 static const double axisTitleSpaceVertical = 2.0;	// Space between labels and title
 
-StatsAxis::StatsAxis(const QString &titleIn, bool horizontal, bool labelsBetweenTicks) :
-	horizontal(horizontal), labelsBetweenTicks(labelsBetweenTicks),
+StatsAxis::StatsAxis(StatsView &view, const QString &title, bool horizontal, bool labelsBetweenTicks) :
+	ChartPixmapItem(view, ChartZValue::Axes),
+	line(view.createChartItem<ChartLineItem>(ChartZValue::Axes, axisColor, axisWidth)),
+	title(title), horizontal(horizontal), labelsBetweenTicks(labelsBetweenTicks),
 	size(1.0), zeroOnScreen(0.0), min(0.0), max(1.0), labelWidth(0.0)
 {
-	// use a Light version of the application fond for both labels and title
+	// use a Light version of the application font for both labels and title
 	labelFont = QFont();
 	labelFont.setWeight(QFont::Light);
 	titleFont = labelFont;
-	setPen(QPen(axisColor, axisWidth));
-	setZValue(ZValues::axes);
-	if (!titleIn.isEmpty()) {
-		title.reset(new QGraphicsSimpleTextItem(titleIn, this));
-		title->setFont(titleFont);
-		title->setBrush(darkLabelColor);
-		if (!horizontal)
-			title->setRotation(-90.0);
-	}
+	QFontMetrics fm(titleFont);
+	titleWidth = title.isEmpty() ? 0.0
+				     : static_cast<double>(fm.size(Qt::TextSingleLine, title).width());
 }
 
 StatsAxis::~StatsAxis()
@@ -101,7 +98,7 @@ int StatsAxis::guessNumTicks(const std::vector<QString> &strings) const
 
 double StatsAxis::titleSpace() const
 {
-	if (!title)
+	if (title.isEmpty())
 		return 0.0;
 	return horizontal ? QFontMetrics(titleFont).height() + axisTitleSpaceHorizontal
 			  : QFontMetrics(titleFont).height() + axisTitleSpaceVertical;
@@ -124,31 +121,14 @@ double StatsAxis::height() const
 	       (labelsBetweenTicks ? 0.0 : axisTickSizeHorizontal);
 }
 
-StatsAxis::Label::Label(const QString &name, double pos, QGraphicsScene *scene, const QFont &font) :
-	label(createItem<QGraphicsSimpleTextItem>(scene, name)),
-	pos(pos)
-{
-	label->setBrush(QBrush(darkLabelColor));
-	label->setFont(font);
-	label->setZValue(ZValues::axes);
-}
-
-void StatsAxis::addLabel(const QString &label, double pos)
+void StatsAxis::addLabel(const QFontMetrics &fm, const QString &label, double pos)
 {
-	labels.emplace_back(label, pos, scene(), labelFont);
-}
-
-StatsAxis::Tick::Tick(double pos, QGraphicsScene *scene) :
-	item(createItemPtr<QGraphicsLineItem>(scene)),
-	pos(pos)
-{
-	item->setPen(QPen(axisColor, axisTickWidth));
-	item->setZValue(ZValues::axes);
+	labels.push_back({ label, fm.size(Qt::TextSingleLine, label).width(), pos });
 }
 
 void StatsAxis::addTick(double pos)
 {
-	ticks.emplace_back(pos, scene());
+	ticks.push_back({ view.createChartItem<ChartLineItem>(ChartZValue::Axes, axisColor, axisTickWidth), pos });
 }
 
 std::vector<double> StatsAxis::ticksPositions() const
@@ -178,60 +158,105 @@ double StatsAxis::toValue(double pos) const
 void StatsAxis::setSize(double sizeIn)
 {
 	size = sizeIn;
+
+	labels.clear();
+	ticks.clear();
 	updateLabels();
+
 	labelWidth = 0.0;
 	for (const Label &label: labels) {
-		double w = label.label->boundingRect().width();
-		if (w > labelWidth)
-			labelWidth = w;
+		if (label.width > labelWidth)
+			labelWidth = label.width;
+	}
+
+	QFontMetrics fm(labelFont);
+	int fontHeight = fm.height();
+	if (horizontal) {
+		double pixmapWidth = size;
+		double offsetX = 0.0;
+		if (!labels.empty() && !labelsBetweenTicks) {
+			pixmapWidth += labels.front().width / 2.0 + labels.back().width / 2.0;
+			offsetX += labels.front().width / 2.0;
+		}
+
+		double pixmapHeight = fontHeight + titleSpace();
+		double offsetY = -axisWidth / 2.0 - axisLabelSpaceHorizontal -
+				 (labelsBetweenTicks ? 0.0 : axisTickSizeHorizontal);
+
+		ChartPixmapItem::resize(QSizeF(pixmapWidth, pixmapHeight)); // Note: this rounds the dimensions up
+		offset = QPointF(round(offsetX), round(offsetY));
+		img->fill(Qt::transparent);
+
+		painter->setPen(QPen(darkLabelColor));
+		painter->setFont(labelFont);
+		for (const Label &label: labels) {
+			double x = (label.pos - min) / (max - min) * size + offset.x() - round(label.width / 2.0);
+			QRectF rect(x, 0.0, label.width, fontHeight);
+			painter->drawText(rect, label.label);
+		}
+		if (!title.isEmpty()) {
+			QRectF rect(offset.x() + round((size - titleWidth) / 2.0),
+				    fontHeight + axisTitleSpaceHorizontal,
+				    titleWidth, fontHeight);
+			painter->setFont(titleFont);
+			painter->drawText(rect, title);
+		}
+	} else {
+		double pixmapWidth = labelWidth + titleSpace();
+		double offsetX = pixmapWidth + axisLabelSpaceVertical + (labelsBetweenTicks ? 0.0 : axisTickSizeVertical);
+
+		double pixmapHeight = ceil(size + axisTickWidth);
+		double offsetY = size;
+		if (!labels.empty() && !labelsBetweenTicks) {
+			pixmapHeight += fontHeight;
+			offsetY += fontHeight / 2.0;
+		}
+
+		ChartPixmapItem::resize(QSizeF(pixmapWidth, pixmapHeight)); // Note: this rounds the dimensions up
+		offset = QPointF(round(offsetX), round(offsetY));
+		img->fill(Qt::transparent);
+
+		painter->setPen(QPen(darkLabelColor));
+		painter->setFont(labelFont);
+		for (const Label &label: labels) {
+			double y = (min - label.pos) / (max - min) * size + offset.y() - round(fontHeight / 2.0);
+			QRectF rect(pixmapWidth - label.width, y, label.width, fontHeight);
+			painter->drawText(rect, label.label);
+		}
+		if (!title.isEmpty()) {
+			painter->rotate(-90.0);
+			QRectF rect(round(-(offsetY + titleWidth) / 2.0), 0.0, titleWidth, fontHeight);
+			painter->setFont(titleFont);
+			painter->drawText(rect, title);
+			painter->resetTransform();
+		}
 	}
 }
 
 void StatsAxis::setPos(QPointF pos)
 {
+	zeroOnScreen = horizontal ? pos.x() : pos.y();
+	ChartPixmapItem::setPos(pos - offset);
+
 	if (horizontal) {
-		zeroOnScreen = pos.x();
-		double labelY = pos.y() + axisLabelSpaceHorizontal +
-				(labelsBetweenTicks ? 0.0 : axisTickSizeHorizontal);
 		double y = pos.y();
-		for (Label &label: labels) {
-			double x = toScreen(label.pos) - label.label->boundingRect().width() / 2.0;
-			label.label->setPos(QPointF(x, labelY));
-		}
-		for (Tick &tick: ticks) {
+		for (const Tick &tick: ticks) {
 			double x = toScreen(tick.pos);
-			tick.item->setLine(x, y, x, y + axisTickSizeHorizontal);
+			tick.item->setLine(QPointF(x, y), QPointF(x, y + axisTickSizeHorizontal));
 		}
-		setLine(zeroOnScreen, y, zeroOnScreen + size, y);
-		if (title)
-			title->setPos(zeroOnScreen + (size - title->boundingRect().width()) / 2.0,
-				      labelY + QFontMetrics(labelFont).height() + axisTitleSpaceHorizontal);
+		line->setLine(QPointF(zeroOnScreen, y), QPointF(zeroOnScreen + size, y));
 	} else {
-		double fontHeight = QFontMetrics(labelFont).height();
-		zeroOnScreen = pos.y();
 		double x = pos.x();
-		double labelX = x - axisLabelSpaceVertical -
-				(labelsBetweenTicks ? 0.0 : axisTickSizeVertical);
-		for (Label &label: labels) {
-			double y = toScreen(label.pos) - fontHeight / 2.0;
-			label.label->setPos(QPointF(labelX - label.label->boundingRect().width(), y));
-		}
-		for (Tick &tick: ticks) {
+		for (const Tick &tick: ticks) {
 			double y = toScreen(tick.pos);
-			tick.item->setLine(x, y, x - axisTickSizeVertical, y);
+			tick.item->setLine(QPointF(x, y), QPointF(x - axisTickSizeVertical, y));
 		}
-		// This is very confusing: even though we need the height of the title, the correct
-		// size is stored in boundingRect().width(). Presumably because the item is rotated
-		// by -90°. Apparently, the boundingRect is in item-local coordinates?
-		if (title)
-			title->setPos(labelX - labelWidth - QFontMetrics(labelFont).height() - axisTitleSpaceVertical,
-				      zeroOnScreen - (size - title->boundingRect().width()) / 2.0);
-		setLine(x, zeroOnScreen, x, zeroOnScreen - size);
+		line->setLine(QPointF(x, zeroOnScreen), QPointF(x, zeroOnScreen - size));
 	}
 }
 
-ValueAxis::ValueAxis(const QString &title, double min, double max, int decimals, bool horizontal) :
-	StatsAxis(title, horizontal, false),
+ValueAxis::ValueAxis(StatsView &view, const QString &title, double min, double max, int decimals, bool horizontal) :
+	StatsAxis(view, title, horizontal, false),
 	min(min), max(max), decimals(decimals)
 {
 	// Avoid degenerate cases
@@ -251,9 +276,6 @@ std::pair<QString, QString> ValueAxis::getFirstLastLabel() const
 
 void ValueAxis::updateLabels()
 {
-	labels.clear();
-	ticks.clear();
-
 	QLocale loc;
 	auto [minString, maxString] = getFirstLastLabel();
 	int numTicks = guessNumTicks({ minString, maxString});
@@ -283,15 +305,16 @@ void ValueAxis::updateLabels()
 	double act = actMin;
 	labels.reserve(num + 1);
 	ticks.reserve(num + 1);
+	QFontMetrics fm(labelFont);
 	for (int i = 0; i <= num; ++i) {
-		addLabel(loc.toString(act, 'f', decimals), act);
+		addLabel(fm, loc.toString(act, 'f', decimals), act);
 		addTick(act);
 		act += actStep;
 	}
 }
 
-CountAxis::CountAxis(const QString &title, int count, bool horizontal) :
-	ValueAxis(title, 0.0, (double)count, 0, horizontal),
+CountAxis::CountAxis(StatsView &view, const QString &title, int count, bool horizontal) :
+	ValueAxis(view, title, 0.0, (double)count, 0, horizontal),
 	count(count)
 {
 }
@@ -306,9 +329,6 @@ std::pair<QString, QString> CountAxis::getFirstLastLabel() const
 
 void CountAxis::updateLabels()
 {
-	labels.clear();
-	ticks.clear();
-
 	QLocale loc;
 	QString countString = loc.toString(count);
 	int numTicks = guessNumTicks({ countString });
@@ -345,14 +365,15 @@ void CountAxis::updateLabels()
 
 	labels.reserve(max + 1);
 	ticks.reserve(max + 1);
+	QFontMetrics fm(labelFont);
 	for (int i = 0; i <= max; i += step) {
-		addLabel(loc.toString(i), static_cast<double>(i));
+		addLabel(fm, loc.toString(i), static_cast<double>(i));
 		addTick(static_cast<double>(i));
 	}
 }
 
-CategoryAxis::CategoryAxis(const QString &title, const std::vector<QString> &labels, bool horizontal) :
-	StatsAxis(title, horizontal, true),
+CategoryAxis::CategoryAxis(StatsView &view, const QString &title, const std::vector<QString> &labels, bool horizontal) :
+	StatsAxis(view, title, horizontal, true),
 	labelsText(labels)
 {
 	setRange(-0.5, static_cast<double>(labels.size()) + 0.5);
@@ -392,8 +413,6 @@ void CategoryAxis::updateLabels()
 
 	QString ellipsis = horizontal ? getEllipsis(fm, size_per_label) : QString();
 
-	labels.clear();
-	ticks.clear();
 	labels.reserve(labelsText.size());
 	ticks.reserve(labelsText.size() + 1);
 	double pos = 0.0;
@@ -401,18 +420,18 @@ void CategoryAxis::updateLabels()
 	for (const QString &s: labelsText) {
 		if (horizontal) {
 			double width = static_cast<double>(fm.size(Qt::TextSingleLine, s).width());
-			addLabel(width < size_per_label ? s : ellipsis, pos);
+			addLabel(fm, width < size_per_label ? s : ellipsis, pos);
 		} else {
 			if (fontHeight < size_per_label)
-				addLabel(s, pos);
+				addLabel(fm, s, pos);
 		}
 		addTick(pos + 0.5);
 		pos += 1.0;
 	}
 }
 
-HistogramAxis::HistogramAxis(const QString &title, std::vector<HistogramAxisEntry> bins, bool horizontal) :
-	StatsAxis(title, horizontal, false),
+HistogramAxis::HistogramAxis(StatsView &view, const QString &title, std::vector<HistogramAxisEntry> bins, bool horizontal) :
+	StatsAxis(view, title, horizontal, false),
 	bin_values(std::move(bins))
 {
 	if (bin_values.size() < 2) // Less than two makes no sense -> there must be at least one category
@@ -446,9 +465,6 @@ std::pair<QString, QString> HistogramAxis::getFirstLastLabel() const
 // There, we obviously want to show the years and not the quarters.
 void HistogramAxis::updateLabels()
 {
-	labels.clear();
-	ticks.clear();
-
 	if (bin_values.size() < 2) // Less than two makes no sense -> there must be at least one category
 		return;
 
@@ -488,9 +504,10 @@ void HistogramAxis::updateLabels()
 	if (first != 0)
 		addTick(bin_values.front().value);
 	int last = first;
+	QFontMetrics fm(labelFont);
 	for (int i = first; i < (int)bin_values.size(); i += step) {
 		const auto &[name, value, recommended] = bin_values[i];
-		addLabel(name, value);
+		addLabel(fm, name, value);
 		addTick(value);
 		last = i;
 	}
@@ -617,7 +634,7 @@ static std::vector<HistogramAxisEntry> timeRangeToBins(double from, double to)
 	return res;
 }
 
-DateAxis::DateAxis(const QString &title, double from, double to, bool horizontal) :
-	HistogramAxis(title, timeRangeToBins(from, to), horizontal)
+DateAxis::DateAxis(StatsView &view, const QString &title, double from, double to, bool horizontal) :
+	HistogramAxis(view, title, timeRangeToBins(from, to), horizontal)
 {
 }
diff --git a/stats/statsaxis.h b/stats/statsaxis.h
index 9d46f753a..89c9edbe2 100644
--- a/stats/statsaxis.h
+++ b/stats/statsaxis.h
@@ -2,15 +2,19 @@
 #ifndef STATS_AXIS_H
 #define STATS_AXIS_H
 
+#include "chartitem.h"
+
 #include <memory>
 #include <vector>
 #include <QFont>
-#include <QGraphicsSimpleTextItem>
-#include <QGraphicsLineItem>
 
-class QGraphicsScene;
+class StatsView;
+class ChartLineItem;
+class QFontMetrics;
 
-class StatsAxis : public QGraphicsLineItem {
+// The labels and the title of the axis are rendered into a pixmap.
+// The ticks and the baseline are realized as individual ChartLineItems.
+class StatsAxis : public ChartPixmapItem {
 public:
 	virtual ~StatsAxis();
 	// Returns minimum and maximum of shown range, not of data points.
@@ -30,22 +34,25 @@ public:
 
 	std::vector<double> ticksPositions() const; // Positions in screen coordinates
 protected:
-	StatsAxis(const QString &title, bool horizontal, bool labelsBetweenTicks);
+	StatsAxis(StatsView &view, const QString &title, bool horizontal, bool labelsBetweenTicks);
+
+	std::unique_ptr<ChartLineItem> line;
+	QString title;
+	double titleWidth;
 
 	struct Label {
-		std::unique_ptr<QGraphicsSimpleTextItem> label;
+		QString label;
+		int width;
 		double pos;
-		Label(const QString &name, double pos, QGraphicsScene *scene, const QFont &font);
 	};
 	std::vector<Label> labels;
-	void addLabel(const QString &label, double pos);
+	void addLabel(const QFontMetrics &fm, const QString &label, double pos);
 	virtual void updateLabels() = 0;
 	virtual std::pair<QString, QString> getFirstLastLabel() const = 0;
 
 	struct Tick {
-		std::unique_ptr<QGraphicsLineItem> item;
+		std::unique_ptr<ChartLineItem> item;
 		double pos;
-		Tick(double pos, QGraphicsScene *scene);
 	};
 	std::vector<Tick> ticks;
 	void addTick(double pos);
@@ -55,9 +62,9 @@ protected:
 	bool labelsBetweenTicks;	// When labels are between ticks, they can be moved closer to the axis
 
 	QFont labelFont, titleFont;
-	std::unique_ptr<QGraphicsSimpleTextItem> title;
 	double size;			// width for horizontal, height for vertical
 	double zeroOnScreen;
+	QPointF offset;			// Offset of the label and title pixmap with respect to the (0,0) position.
 	double min, max;
 	double labelWidth;		// Maximum width of labels
 private:
@@ -66,7 +73,7 @@ private:
 
 class ValueAxis : public StatsAxis {
 public:
-	ValueAxis(const QString &title, double min, double max, int decimals, bool horizontal);
+	ValueAxis(StatsView &view, const QString &title, double min, double max, int decimals, bool horizontal);
 private:
 	double min, max;
 	int decimals;
@@ -76,7 +83,7 @@ private:
 
 class CountAxis : public ValueAxis {
 public:
-	CountAxis(const QString &title, int count, bool horizontal);
+	CountAxis(StatsView &view, const QString &title, int count, bool horizontal);
 private:
 	int count;
 	void updateLabels() override;
@@ -85,7 +92,7 @@ private:
 
 class CategoryAxis : public StatsAxis {
 public:
-	CategoryAxis(const QString &title, const std::vector<QString> &labels, bool horizontal);
+	CategoryAxis(StatsView &view, const QString &title, const std::vector<QString> &labels, bool horizontal);
 private:
 	std::vector<QString> labelsText;
 	void updateLabels();
@@ -100,7 +107,7 @@ struct HistogramAxisEntry {
 
 class HistogramAxis : public StatsAxis {
 public:
-	HistogramAxis(const QString &title, std::vector<HistogramAxisEntry> bin_values, bool horizontal);
+	HistogramAxis(StatsView &view, const QString &title, std::vector<HistogramAxisEntry> bin_values, bool horizontal);
 private:
 	void updateLabels() override;
 	std::pair<QString, QString> getFirstLastLabel() const override;
@@ -110,7 +117,7 @@ private:
 
 class DateAxis : public HistogramAxis {
 public:
-	DateAxis(const QString &title, double from, double to, bool horizontal);
+	DateAxis(StatsView &view, const QString &title, double from, double to, bool horizontal);
 };
 
 #endif
diff --git a/stats/statsview.cpp b/stats/statsview.cpp
index 83a586456..e893c3ebb 100644
--- a/stats/statsview.cpp
+++ b/stats/statsview.cpp
@@ -38,6 +38,7 @@ StatsView::StatsView(QQuickItem *parent) : QQuickItem(parent),
 	draggedItem(nullptr),
 	rootNode(nullptr)
 {
+	chartItems.reset(new std::vector<ChartItem *>[(size_t)ChartZValue::Count]);
 	setFlag(ItemHasContents, true);
 
 	connect(&diveListNotifier, &DiveListNotifier::numShownChanged, this, &StatsView::replotIfVisible);
@@ -89,7 +90,6 @@ public:
 	QSGImageNode *imageNode; // imageNode to plot QGRaphicsScene on. Remove in due course.
 	// We entertain one node per Z-level.
 	std::array<QSGNode *, (size_t)ChartZValue::Count> zNodes;
-	std::array<std::vector<ChartItem *>, (size_t)ChartZValue::Count> items;
 };
 
 RootNode::RootNode(QQuickWindow *w)
@@ -124,8 +124,8 @@ QSGNode *StatsView::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNod
 		plotAreaChanged(plotRect.size());
 	}
 
-	for (auto &v: n->items) {
-		for (ChartItem *item: v) {
+	for (int i = 0; i < (int)ChartZValue::Count; ++i) {
+		for (ChartItem *item: chartItems[i]) {
 			if (item->dirty)
 				item->render();
 		}
@@ -151,7 +151,7 @@ void StatsView::addQSGNode(QSGNode *node, ChartZValue z)
 void StatsView::unregisterChartItem(const ChartItem *item)
 {
 	int idx = std::clamp((int)item->zValue, 0, (int)ChartZValue::Count - 1);
-	std::vector<ChartItem *> &v = rootNode->items[idx];
+	std::vector<ChartItem *> &v = chartItems[idx];
 	auto it = std::find(v.begin(), v.end(), item);
 	if (it != v.end())
 		v.erase(it);
@@ -160,7 +160,7 @@ void StatsView::unregisterChartItem(const ChartItem *item)
 void StatsView::registerChartItem(ChartItem *item)
 {
 	int idx = std::clamp((int)item->zValue, 0, (int)ChartZValue::Count - 1);
-	rootNode->items[idx].push_back(item);
+	chartItems[idx].push_back(item);
 }
 
 QQuickWindow *StatsView::w() const
@@ -307,8 +307,9 @@ void StatsView::updateTitlePos()
 template <typename T, class... Args>
 T *StatsView::createAxis(const QString &title, Args&&... args)
 {
-	T *res = createItem<T>(&scene, title, std::forward<Args>(args)...);
-	axes.emplace_back(res);
+	std::unique_ptr<T> ptr = createChartItem<T>(title, std::forward<Args>(args)...);
+	T *res = ptr.get();
+	axes.push_back(std::move(ptr));
 	return res;
 }
 
@@ -326,8 +327,8 @@ void StatsView::reset()
 	xAxis = yAxis = nullptr;
 	draggedItem = nullptr;
 	if (rootNode) {
-		for (auto &v: rootNode->items)
-			v.clear(); // non-owning pointers
+		for (int i = 0; i < (int)ChartZValue::Count; ++i)
+			chartItems[i].clear(); // non-owning pointers
 	}
 	legend.reset();
 	series.clear();
diff --git a/stats/statsview.h b/stats/statsview.h
index aad9ec977..c8e850d9b 100644
--- a/stats/statsview.h
+++ b/stats/statsview.h
@@ -142,6 +142,7 @@ private:
 
 	StatsState state;
 	QFont titleFont;
+	std::unique_ptr<std::vector<ChartItem *>[]> chartItems;
 	std::vector<std::unique_ptr<StatsAxis>> axes;
 	std::unique_ptr<StatsGrid> grid;
 	std::vector<std::unique_ptr<StatsSeries>> series;