statistics: convert QuartileMarkers to QSGNodes

Slowly converting the QGraphicsScene items to QSGNodes to
avoid full replot of the scene.

This adds a new abstraction for line-nodes. Since the render()
function here is fundamentally different from the pixmap-nodes
we had so far, this has to be made virtual.

Also, move the quartile markers to their own source file,
since the StatsView source file is quite huge already.

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

8 files changed, 172 insertions, 58 deletions

diff --git a/Subsurface-mobile.pro b/Subsurface-mobile.pro
index e2a724633..b113eebfe 100644
--- a/Subsurface-mobile.pro
+++ b/Subsurface-mobile.pro
@@ -136,6 +136,7 @@ SOURCES += subsurface-mobile-main.cpp \
 	stats/informationbox.cpp \
 	stats/legend.cpp \
 	stats/pieseries.cpp \
+	stats/quartilemarker.cpp \
 	stats/scatterseries.cpp \
 	stats/statsaxis.cpp \
 	stats/statscolors.cpp \
@@ -285,6 +286,7 @@ HEADERS += \
 	stats/informationbox.h \
 	stats/legend.h \
 	stats/pieseries.h \
+	stats/quartilemarker.h \
 	stats/scatterseries.h \
 	stats/statsaxis.h \
 	stats/statscolors.h \
diff --git a/stats/CMakeLists.txt b/stats/CMakeLists.txt
index c0fbe3c51..105096436 100644
--- a/stats/CMakeLists.txt
+++ b/stats/CMakeLists.txt
@@ -19,6 +19,8 @@ set(SUBSURFACE_STATS_SRCS
 	legend.cpp
 	pieseries.h
 	pieseries.cpp
+	quartilemarker.h
+	quartilemarker.cpp
 	scatterseries.h
 	scatterseries.cpp
 	statsaxis.h
diff --git a/stats/chartitem.cpp b/stats/chartitem.cpp
index 68e7fa371..6fef5e44f 100644
--- a/stats/chartitem.cpp
+++ b/stats/chartitem.cpp
@@ -4,6 +4,7 @@
 
 #include <cmath>
 #include <QQuickWindow>
+#include <QSGFlatColorMaterial>
 #include <QSGImageNode>
 #include <QSGTexture>
 
@@ -13,13 +14,12 @@ static int round_up(double f)
 }
 
 ChartItem::ChartItem(StatsView &v, ChartZValue z) :
-	dirty(false), zValue(z), view(v), positionDirty(false), textureDirty(false)
+	dirty(false), zValue(z), view(v)
 {
 }
 
 ChartItem::~ChartItem()
 {
-	painter.reset(); // Make sure to destroy painter before image that is painted on
 	view.unregisterChartItem(this);
 }
 
@@ -28,19 +28,29 @@ QSizeF ChartItem::sceneSize() const
 	return view.size();
 }
 
-void ChartItem::setTextureDirty()
+ChartPixmapItem::ChartPixmapItem(StatsView &v, ChartZValue z) : ChartItem(v, z),
+	positionDirty(false), textureDirty(false)
+{
+}
+
+ChartPixmapItem::~ChartPixmapItem()
+{
+	painter.reset(); // Make sure to destroy painter before image that is painted on
+}
+
+void ChartPixmapItem::setTextureDirty()
 {
 	textureDirty = true;
 	dirty = true;
 }
 
-void ChartItem::setPositionDirty()
+void ChartPixmapItem::setPositionDirty()
 {
 	positionDirty = true;
 	dirty = true;
 }
 
-void ChartItem::render()
+void ChartPixmapItem::render()
 {
 	if (!dirty)
 		return;
@@ -64,7 +74,7 @@ void ChartItem::render()
 	dirty = false;
 }
 
-void ChartItem::resize(QSizeF size)
+void ChartPixmapItem::resize(QSizeF size)
 {
 	painter.reset();
 	img.reset(new QImage(round_up(size.width()), round_up(size.height()), QImage::Format_ARGB32));
@@ -74,19 +84,19 @@ void ChartItem::resize(QSizeF size)
 	setTextureDirty();
 }
 
-void ChartItem::setPos(QPointF pos)
+void ChartPixmapItem::setPos(QPointF pos)
 {
 	rect.moveTopLeft(pos);
 	setPositionDirty();
 }
 
-QRectF ChartItem::getRect() const
+QRectF ChartPixmapItem::getRect() const
 {
 	return rect;
 }
 
 ChartRectItem::ChartRectItem(StatsView &v, ChartZValue z,
-			     const QPen &pen, const QBrush &brush, double radius) : ChartItem(v, z),
+			     const QPen &pen, const QBrush &brush, double radius) : ChartPixmapItem(v, z),
 	pen(pen), brush(brush), radius(radius)
 {
 }
@@ -97,7 +107,7 @@ ChartRectItem::~ChartRectItem()
 
 void ChartRectItem::resize(QSizeF size)
 {
-	ChartItem::resize(size);
+	ChartPixmapItem::resize(size);
 	img->fill(Qt::transparent);
 	painter->setPen(pen);
 	painter->setBrush(brush);
@@ -106,3 +116,50 @@ void ChartRectItem::resize(QSizeF size)
 	QRect rect(width / 2, width / 2, imgSize.width() - width, imgSize.height() - width);
 	painter->drawRoundedRect(rect, radius, radius, Qt::AbsoluteSize);
 }
+
+ChartLineItem::ChartLineItem(StatsView &v, ChartZValue z, QColor color, double width) : ChartItem(v, z),
+	color(color), width(width), positionDirty(false), materialDirty(false)
+{
+}
+
+ChartLineItem::~ChartLineItem()
+{
+}
+
+void ChartLineItem::render()
+{
+	if (!node) {
+		geometry.reset(new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 2));
+		geometry->setDrawingMode(QSGGeometry::DrawLines);
+		material.reset(new QSGFlatColorMaterial);
+		node.reset(new QSGGeometryNode);
+		node->setGeometry(geometry.get());
+		node->setMaterial(material.get());
+		view.addQSGNode(node.get(), zValue);
+		positionDirty = materialDirty = true;
+	}
+
+	if (positionDirty) {
+		// Attention: width is a geometry property and therefore handled by position dirty!
+		geometry->setLineWidth(static_cast<float>(width));
+		auto vertices = geometry->vertexDataAsPoint2D();
+		vertices[0].set(static_cast<float>(from.x()), static_cast<float>(from.y()));
+		vertices[1].set(static_cast<float>(to.x()), static_cast<float>(to.y()));
+		node->markDirty(QSGNode::DirtyGeometry);
+	}
+
+	if (materialDirty) {
+		material->setColor(color);
+		node->markDirty(QSGNode::DirtyMaterial);
+	}
+
+	positionDirty = materialDirty = false;
+}
+
+void ChartLineItem::setLine(QPointF fromIn, QPointF toIn)
+{
+	from = fromIn;
+	to = toIn;
+	positionDirty = true;
+	dirty = true;
+}
diff --git a/stats/chartitem.h b/stats/chartitem.h
index 8cb9ef3a7..5dab8d1ea 100644
--- a/stats/chartitem.h
+++ b/stats/chartitem.h
@@ -7,6 +7,9 @@
 #include <memory>
 #include <QPainter>
 
+class QSGGeometry;
+class QSGGeometryNode;
+class QSGFlatColorMaterial;
 class QSGImageNode;
 class QSGTexture;
 class StatsView;
@@ -15,31 +18,41 @@ enum class ChartZValue : int;
 class ChartItem {
 public:
 	ChartItem(StatsView &v, ChartZValue z);
-	~ChartItem();
-	// Attention: The children are responsible for updating the item. None of these calls will.
-	void resize(QSizeF size);	// Resets the canvas. Attention: image is *unitialized*.
-	void setPos(QPointF pos);
-	void render();			// Only call on render thread!
+	virtual ~ChartItem();
+	virtual void render() = 0;	// Only call on render thread!
 	QRectF getRect() const;
 	bool dirty;			// If true, call render() when rebuilding the scene
 	const ChartZValue zValue;
 protected:
+	QSizeF sceneSize() const;
+	StatsView &view;
+};
+
+// A chart item that blits a precalculated pixmap onto the scene.
+class ChartPixmapItem : public ChartItem {
+public:
+	ChartPixmapItem(StatsView &v, ChartZValue z);
+	~ChartPixmapItem();
+
+	void setPos(QPointF pos);
+	void render() override;		// Only call on render thread!
+	QRectF getRect() const;
+protected:
+	void resize(QSizeF size);	// Resets the canvas. Attention: image is *unitialized*.
 	std::unique_ptr<QPainter> painter;
 	std::unique_ptr<QImage> img;
-	QSizeF sceneSize() const;
 	void setTextureDirty();
 	void setPositionDirty();
 private:
-	StatsView &view;
 	QRectF rect;
-	bool positionDirty;
-	bool textureDirty;
+	bool positionDirty;		// true if the position changed since last render
+	bool textureDirty;		// true if the pixmap changed since last render
 	std::unique_ptr<QSGImageNode> node;
 	std::unique_ptr<QSGTexture> texture;
 };
 
 // Draw a rectangular background after resize. Children are responsible for calling update().
-class ChartRectItem : public ChartItem {
+class ChartRectItem : public ChartPixmapItem {
 public:
 	ChartRectItem(StatsView &v, ChartZValue z, const QPen &pen, const QBrush &brush, double radius);
 	~ChartRectItem();
@@ -50,4 +63,21 @@ private:
 	double radius;
 };
 
+class ChartLineItem : public ChartItem {
+public:
+	ChartLineItem(StatsView &v, ChartZValue z, QColor color, double width);
+	~ChartLineItem();
+	void setLine(QPointF from, QPointF to);
+	void render() override;		// Only call on render thread!
+private:
+	QPointF from, to;
+	QColor color;
+	double width;
+	bool positionDirty;
+	bool materialDirty;
+	std::unique_ptr<QSGGeometryNode> node;
+	std::unique_ptr<QSGFlatColorMaterial> material;
+	std::unique_ptr<QSGGeometry> geometry;
+};
+
 #endif
diff --git a/stats/quartilemarker.cpp b/stats/quartilemarker.cpp
new file mode 100644
index 000000000..ace019df5
--- /dev/null
+++ b/stats/quartilemarker.cpp
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "quartilemarker.h"
+#include "statsaxis.h"
+#include "zvalues.h"
+
+static const QColor quartileMarkerColor(Qt::red);
+static const double quartileMarkerSize = 15.0;
+
+QuartileMarker::QuartileMarker(StatsView &view, double pos, double value, StatsAxis *xAxis, StatsAxis *yAxis) :
+	ChartLineItem(view, ChartZValue::ChartFeatures, quartileMarkerColor, 2.0),
+	xAxis(xAxis), yAxis(yAxis),
+	pos(pos),
+	value(value)
+{
+	updatePosition();
+}
+
+QuartileMarker::~QuartileMarker()
+{
+}
+
+void QuartileMarker::updatePosition()
+{
+	if (!xAxis || !yAxis)
+		return;
+	double x = xAxis->toScreen(pos);
+	double y = yAxis->toScreen(value);
+	setLine(QPointF(x - quartileMarkerSize / 2.0, y),
+		QPointF(x + quartileMarkerSize / 2.0, y));
+}
diff --git a/stats/quartilemarker.h b/stats/quartilemarker.h
new file mode 100644
index 000000000..2e754248d
--- /dev/null
+++ b/stats/quartilemarker.h
@@ -0,0 +1,20 @@
+// A short line used to mark quartiles
+#ifndef QUARTILE_MARKER_H
+#define QUARTILE_MARKER_H
+
+#include "chartitem.h"
+
+class StatsAxis;
+class StatsView;
+
+class QuartileMarker : public ChartLineItem {
+public:
+	QuartileMarker(StatsView &view, double pos, double value, StatsAxis *xAxis, StatsAxis *yAxis);
+	~QuartileMarker();
+	void updatePosition();
+private:
+	StatsAxis *xAxis, *yAxis;
+	double pos, value;
+};
+
+#endif
diff --git a/stats/statsview.cpp b/stats/statsview.cpp
index f07b00896..b4b82ccfa 100644
--- a/stats/statsview.cpp
+++ b/stats/statsview.cpp
@@ -4,6 +4,7 @@
 #include "boxseries.h"
 #include "legend.h"
 #include "pieseries.h"
+#include "quartilemarker.h"
 #include "scatterseries.h"
 #include "statsaxis.h"
 #include "statscolors.h"
@@ -25,8 +26,6 @@
 #include <QSGTexture>
 
 // Constants that control the graph layouts
-static const QColor quartileMarkerColor(Qt::red);
-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
 
@@ -211,8 +210,8 @@ void StatsView::plotAreaChanged(const QSizeF &s)
 		grid->updatePositions();
 	for (auto &series: series)
 		series->updatePositions();
-	for (QuartileMarker &marker: quartileMarkers)
-		marker.updatePosition();
+	for (auto &marker: quartileMarkers)
+		marker->updatePosition();
 	for (RegressionLine &line: regressionLines)
 		line.updatePosition();
 	for (HistogramMarker &marker: histogramMarkers)
@@ -799,36 +798,18 @@ void StatsView::plotDiscreteScatter(const std::vector<dive *> &dives,
 		if (quartiles) {
 			StatsQuartiles quartiles = StatsVariable::quartiles(array);
 			if (quartiles.isValid()) {
-				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);
+				quartileMarkers.push_back(createChartItem<QuartileMarker>(
+						x, quartiles.q1, catAxis, valAxis));
+				quartileMarkers.push_back(createChartItem<QuartileMarker>(
+						x, quartiles.q2, catAxis, valAxis));
+				quartileMarkers.push_back(createChartItem<QuartileMarker>(
+						x, quartiles.q3, catAxis, valAxis));
 			}
 		}
 		x += 1.0;
 	}
 }
 
-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)
-{
-	item->setZValue(ZValues::chartFeatures);
-	item->setPen(QPen(quartileMarkerColor, 2.0));
-	updatePosition();
-}
-
-void StatsView::QuartileMarker::updatePosition()
-{
-	if (!xAxis || !yAxis)
-		return;
-	double x = xAxis->toScreen(pos);
-	double y = yAxis->toScreen(value);
-	item->setLine(x - quartileMarkerSize / 2.0, y,
-		      x + quartileMarkerSize / 2.0, y);
-}
-
 StatsView::RegressionLine::RegressionLine(const struct regression_data reg, QBrush brush, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) :
 	item(createItemPtr<QGraphicsPolygonItem>(scene)),
 	central(createItemPtr<QGraphicsPolygonItem>(scene)),
diff --git a/stats/statsview.h b/stats/statsview.h
index 1a922ac98..073a200fd 100644
--- a/stats/statsview.h
+++ b/stats/statsview.h
@@ -24,6 +24,7 @@ class CategoryAxis;
 class ChartItem;
 class CountAxis;
 class HistogramAxis;
+class QuartileMarker;
 class StatsAxis;
 class StatsGrid;
 class Legend;
@@ -125,15 +126,6 @@ private:
 	// Helper functions to add feature to the chart
 	void addLineMarker(double pos, double low, double high, const QPen &pen, bool isHorizontal);
 
-	// A short line used to mark quartiles
-	struct QuartileMarker {
-		std::unique_ptr<QGraphicsLineItem> item;
-		StatsAxis *xAxis, *yAxis;
-		double pos, value;
-		QuartileMarker(double pos, double value, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis);
-		void updatePosition();
-	};
-
 	// A regression line
 	struct RegressionLine {
 		std::unique_ptr<QGraphicsPolygonItem> item;
@@ -163,7 +155,7 @@ private:
 	std::unique_ptr<StatsGrid> grid;
 	std::vector<std::unique_ptr<StatsSeries>> series;
 	std::unique_ptr<Legend> legend;
-	std::vector<QuartileMarker> quartileMarkers;
+	std::vector<std::unique_ptr<QuartileMarker>> quartileMarkers;
 	std::vector<RegressionLine> regressionLines;
 	std::vector<HistogramMarker> histogramMarkers;
 	std::unique_ptr<QGraphicsSimpleTextItem> title;