statistics: convert scatter series to use QSG

The original plan to reuse the ChartPixmapItem for the
scatteritems was dumped, because it is unclear if the
textures are shared if generated for each item.

Instead, a new ChartScatterItem was created, where all
items share the same textures (one for highlighted,
one for non-highlighted). This means that the rendering
of the scatter items is now done in the chartitem.cpp
file, which feels like a layering violation. Not good,
but the easiest for now.

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

stats/chartitem.cpp

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "chartitem.h"
+#include "statscolors.h"
 #include "statsview.h"
 
 #include <cmath>
@@ -95,6 +96,94 @@ QRectF ChartPixmapItem::getRect() const
 	return rect;
 }
 
+static const int scatterItemDiameter = 10;
+static const int scatterItemBorder = 1;
+
+ChartScatterItem::ChartScatterItem(StatsView &v, ChartZValue z) : HideableChartItem(v, z),
+	positionDirty(false), textureDirty(false), highlighted(false)
+{
+	rect.setSize(QSizeF(static_cast<double>(scatterItemDiameter), static_cast<double>(scatterItemDiameter)));
+}
+
+ChartScatterItem::~ChartScatterItem()
+{
+}
+
+static std::unique_ptr<QSGTexture> createScatterTexture(StatsView &view, const QColor &color, const QColor &borderColor)
+{
+	QImage img(scatterItemDiameter, scatterItemDiameter, QImage::Format_ARGB32);
+	img.fill(Qt::transparent);
+	QPainter painter(&img);
+	painter.setPen(Qt::NoPen);
+	painter.setRenderHint(QPainter::Antialiasing);
+	painter.setBrush(borderColor);
+	painter.drawEllipse(0, 0, scatterItemDiameter, scatterItemDiameter);
+	painter.setBrush(color);
+	painter.drawEllipse(scatterItemBorder, scatterItemBorder,
+			    scatterItemDiameter - 2 * scatterItemBorder,
+			    scatterItemDiameter - 2 * scatterItemBorder);
+	return std::unique_ptr<QSGTexture>(
+		view.w()->createTextureFromImage(img, QQuickWindow::TextureHasAlphaChannel)
+	);
+}
+
+std::unique_ptr<QSGTexture> scatterItemTexture;
+std::unique_ptr<QSGTexture> scatterItemHighlightedTexture;
+
+void ChartScatterItem::render()
+{
+	if (!scatterItemTexture) {
+		scatterItemTexture = createScatterTexture(view, fillColor, borderColor);
+		scatterItemHighlightedTexture = createScatterTexture(view, highlightedColor, highlightedBorderColor);
+	}
+	if (!node) {
+		createNode(view.w()->createImageNode());
+		view.addQSGNode(node.get(), zValue);
+		textureDirty = positionDirty = true;
+	}
+	if (textureDirty) {
+		node->node->setTexture(highlighted ? scatterItemHighlightedTexture.get() : scatterItemTexture.get());
+		textureDirty = false;
+	}
+	if (positionDirty) {
+		node->node->setRect(rect);
+		positionDirty = false;
+	}
+}
+
+void ChartScatterItem::setPos(QPointF pos)
+{
+	pos -= QPointF(scatterItemDiameter / 2.0, scatterItemDiameter / 2.0);
+	rect.moveTopLeft(pos);
+	positionDirty = true;
+	view.registerDirtyChartItem(*this);
+}
+
+static double squareDist(const QPointF &p1, const QPointF &p2)
+{
+	QPointF diff = p1 - p2;
+	return QPointF::dotProduct(diff, diff);
+}
+
+bool ChartScatterItem::contains(QPointF point) const
+{
+	return squareDist(point, rect.center()) <= (scatterItemDiameter / 2.0) * (scatterItemDiameter / 2.0);
+}
+
+void ChartScatterItem::setHighlight(bool highlightedIn)
+{
+	if (highlighted == highlightedIn)
+		return;
+	highlighted = highlightedIn;
+	textureDirty = true;
+	view.registerDirtyChartItem(*this);
+}
+
+QRectF ChartScatterItem::getRect() const
+{
+	return rect;
+}
+
 ChartRectItem::ChartRectItem(StatsView &v, ChartZValue z,
 			     const QPen &pen, const QBrush &brush, double radius) : ChartPixmapItem(v, z),
 	pen(pen), brush(brush), radius(radius)

stats/chartitem.h

@@ -150,6 +150,26 @@ private:
 	std::unique_ptr<QSGGeometry> whiskersGeometry;
 };
 
+// An item in a scatter chart. This is not simply a normal pixmap item,
+// because we want that all items share the *same* texture for memory
+// efficiency. It is somewhat questionable to define the form of the
+// scatter item here, but so it is for now.
+class ChartScatterItem : public HideableChartProxyItem<QSGImageNode> {
+public:
+	ChartScatterItem(StatsView &v, ChartZValue z);
+	~ChartScatterItem();
+
+	void setPos(QPointF pos);		// Specifies the *center* of the item.
+	void setHighlight(bool highlight);	// In the future, support different kinds of scatter items.
+	void render() override;			// Only call on render thread!
+	QRectF getRect() const;
+	bool contains(QPointF point) const;
+private:
+	QRectF rect;
+	QSizeF textureSize;
+	bool positionDirty, textureDirty;
+	bool highlighted;
+};
 
 // Implementation detail of templates - move to serparate header file
 template <typename Node>

stats/scatterseries.cpp

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "scatterseries.h"
+#include "chartitem.h"
 #include "informationbox.h"
 #include "statscolors.h"
 #include "statshelper.h"
@@ -11,12 +12,6 @@
 #include "core/divelist.h"
 #include "core/qthelper.h"
 
-#include <QGraphicsPixmapItem>
-#include <QPainter>
-
-static const int scatterItemDiameter = 10;
-static const int scatterItemBorder = 1;
-
 ScatterSeries::ScatterSeries(QGraphicsScene *scene, StatsView &view, StatsAxis *xAxis, StatsAxis *yAxis,
 			     const StatsVariable &varX, const StatsVariable &varY) :
 	StatsSeries(scene, view, xAxis, yAxis),
@@ -28,62 +23,28 @@ ScatterSeries::~ScatterSeries()
 {
 }
 
-static QPixmap createScatterPixmap(const QColor &color, const QColor &borderColor)
-{
-	QPixmap res(scatterItemDiameter, scatterItemDiameter);
-	res.fill(Qt::transparent);
-	QPainter painter(&res);
-	painter.setPen(Qt::NoPen);
-	painter.setRenderHint(QPainter::Antialiasing);
-	painter.setBrush(borderColor);
-	painter.drawEllipse(0, 0, scatterItemDiameter, scatterItemDiameter);
-	painter.setBrush(color);
-	painter.drawEllipse(scatterItemBorder, scatterItemBorder,
-			    scatterItemDiameter - 2 * scatterItemBorder,
-			    scatterItemDiameter - 2 * scatterItemBorder);
-	return res;
-}
-
-// Annoying: we can create a QPixmap only after the application was initialized.
-// Therefore, do this as a on-demand initialized pointer. A function local static
-// variable does unnecesssary (in this case) thread synchronization.
-static std::unique_ptr<QPixmap> scatterPixmapPtr;
-static std::unique_ptr<QPixmap> scatterPixmapHighlightedPtr;
-
-static const QPixmap &scatterPixmap(bool highlight)
-{
-	if (!scatterPixmapPtr) {
-		scatterPixmapPtr.reset(new QPixmap(createScatterPixmap(fillColor, ::borderColor)));
-		scatterPixmapHighlightedPtr.reset(new QPixmap(createScatterPixmap(highlightedColor, highlightedBorderColor)));
-	}
-	return highlight ? *scatterPixmapHighlightedPtr : *scatterPixmapPtr;
-}
-
-ScatterSeries::Item::Item(QGraphicsScene *scene, ScatterSeries *series, dive *d, double pos, double value) :
-	item(createItemPtr<QGraphicsPixmapItem>(scene, scatterPixmap(false))),
+ScatterSeries::Item::Item(StatsView &view, ScatterSeries *series, dive *d, double pos, double value) :
+	item(view.createChartItem<ChartScatterItem>(ChartZValue::Series)),
 	d(d),
 	pos(pos),
 	value(value)
 {
-	item->setZValue(ZValues::series);
 	updatePosition(series);
 }
 
 void ScatterSeries::Item::updatePosition(ScatterSeries *series)
 {
-	QPointF center = series->toScreen(QPointF(pos, value));
-	item->setPos(center.x() - scatterItemDiameter / 2.0,
-		     center.y() - scatterItemDiameter / 2.0);
+	item->setPos(series->toScreen(QPointF(pos, value)));
 }
 
 void ScatterSeries::Item::highlight(bool highlight)
 {
-	item->setPixmap(scatterPixmap(highlight));
+	item->setHighlight(highlight);
 }
 
 void ScatterSeries::append(dive *d, double pos, double value)
 {
-	items.emplace_back(scene, this, d, pos, value);
+	items.emplace_back(view, this, d, pos, value);
 }
 
 void ScatterSeries::updatePositions()
@@ -92,35 +53,20 @@ void ScatterSeries::updatePositions()
 		item.updatePosition(this);
 }
 
-static double sq(double f)
-{
-	return f * f;
-}
-
-static double squareDist(const QPointF &p1, const QPointF &p2)
-{
-	QPointF diff = p1 - p2;
-	return QPointF::dotProduct(diff, diff);
-}
-
 std::vector<int> ScatterSeries::getItemsUnderMouse(const QPointF &point) const
 {
 	std::vector<int> res;
 	double x = point.x();
 
-	auto low = std::lower_bound(items.begin(), items.end(), x - scatterItemDiameter,
-				    [] (const Item &item, double x) { return item.item->pos().x() < x; });
-	auto high = std::upper_bound(low, items.end(), x + scatterItemDiameter,
-				    [] (double x, const Item &item) { return x < item.item->pos().x(); });
+	auto low = std::lower_bound(items.begin(), items.end(), x,
+				    [] (const Item &item, double x) { return item.item->getRect().right() < x; });
+	auto high = std::upper_bound(low, items.end(), x,
+				    [] (double x, const Item &item) { return x < item.item->getRect().left(); });
 	// Hopefully that narrows it down enough. For discrete scatter plots, we could also partition
 	// by equal x and do a binary search in these partitions. But that's probably not worth it.
 	res.reserve(high - low);
-	double minSquare = sq(scatterItemDiameter / 2.0 + scatterItemBorder);
 	for (auto it = low; it < high; ++it) {
-		QPointF pos = it->item->pos();
-		pos.rx() += scatterItemDiameter / 2.0 + scatterItemBorder;
-		pos.ry() += scatterItemDiameter / 2.0 + scatterItemBorder;
-		if (squareDist(pos, point) <= minSquare)
+		if (it->item->contains(point))
 			res.push_back(it - items.begin());
 	}
 	return res;

stats/scatterseries.h

@@ -8,10 +8,9 @@
 
 #include <memory>
 #include <vector>
-#include <QGraphicsRectItem>
 
-class QGraphicsPixmapItem;
 class QGraphicsScene;
+class ChartScatterItem;
 struct InformationBox;
 struct StatsVariable;
 struct dive;
@@ -34,10 +33,10 @@ private:
 	std::vector<int> getItemsUnderMouse(const QPointF &f) const;
 
 	struct Item {
-		std::unique_ptr<QGraphicsPixmapItem> item;
+		std::unique_ptr<ChartScatterItem> item;
 		dive *d;
 		double pos, value;
-		Item(QGraphicsScene *scene, ScatterSeries *series, dive *d, double pos, double value);
+		Item(StatsView &view, ScatterSeries *series, dive *d, double pos, double value);
 		void updatePosition(ScatterSeries *series);
 		void highlight(bool highlight);
 	};