stats: break out common QtQuick part of the code

Move most of the QtQuick code to its own directory, so that it
can be reused in the future for the chart.

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

qt-quick/chartview.h

@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef CHART_VIEW_H
+#define CHART_VIEW_H
+
+#include "chartitem_ptr.h"
+
+#include <QQuickItem>
+
+class ChartItem;
+class QSGTexture;
+class RootNode;	// Internal implementation detail
+
+class ChartView : public QQuickItem {
+	Q_OBJECT
+public:
+	ChartView(QQuickItem *parent, size_t maxZ);
+	~ChartView();
+
+	QQuickWindow *w() const;			// Make window available to items
+	QSizeF size() const;
+	QRectF plotArea() const;
+	void setBackgroundColor(QColor color);		// Chart must be replot for color to become effective.
+	void addQSGNode(QSGNode *node, size_t z);	// Must only be called in render thread!
+	void registerChartItem(ChartItem &item);
+	void registerDirtyChartItem(ChartItem &item);
+	void emergencyShutdown();			// Called when QQuick decides to delete our root node.
+
+	// Create a chart item and add it to the scene.
+	// The item must not be deleted by the caller, but can be
+	// scheduled for deletion using deleteChartItem() below.
+	// Most items can be made invisible, which is preferred over deletion.
+	// All items on the scene will be deleted once the chart is reset.
+	template <typename T, class... Args>
+	ChartItemPtr<T> createChartItem(Args&&... args);
+
+	template <typename T>
+	void deleteChartItem(ChartItemPtr<T> &item);
+
+protected:
+	void setLayerVisibility(size_t z, bool visible);
+	void clearItems();
+
+	// This is called when Qt decided to reset our rootNode, which invalidates all items on the chart.
+	// The base class must invalidate all pointers and references.
+	virtual void resetPointers() = 0;
+private:
+	// QtQuick related things
+	size_t maxZ;
+	bool backgroundDirty;
+	QRectF plotRect;
+	QSGNode *updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *updatePaintNodeData) override;
+	QColor backgroundColor;
+
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+	void geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry) override;
+#else
+	void geometryChanged(const QRectF &newGeometry, const QRectF &oldGeometry) override;
+#endif
+	virtual void plotAreaChanged(const QSizeF &size) = 0;
+
+	RootNode *rootNode;
+
+	// There are three double linked lists of chart items:
+	// clean items, dirty items and items to be deleted.
+	// Note that only the render thread must delete chart items,
+	// and therefore these lists are the only owning pointers
+	// to chart items. All other pointers are non-owning and
+	// can therefore become stale.
+	struct ChartItemList {
+		ChartItemList();
+		ChartItem *first, *last;
+		void append(ChartItem &item);
+		void remove(ChartItem &item);
+		void clear();
+		void splice(ChartItemList &list);
+	};
+	ChartItemList cleanItems, dirtyItems, deletedItems;
+	void deleteChartItemInternal(ChartItem &item);
+	void freeDeletedChartItems();
+};
+
+// This implementation detail must be known to users of the class.
+// Perhaps move it into a statsview_impl.h file.
+template <typename T, class... Args>
+ChartItemPtr<T> ChartView::createChartItem(Args&&... args)
+{
+	return ChartItemPtr(new T(*this, std::forward<Args>(args)...));
+}
+
+template <typename T>
+void ChartView::deleteChartItem(ChartItemPtr<T> &item)
+{
+	deleteChartItemInternal(*item);
+	item.reset();
+}
+
+#endif