statistics: add notion of Z-value to chart items

The chart items were drawn in order of creation. To control this,
add a notion of Z-value. In contrast to QGraphicsScene, make
this a small integer value.

To controll order of drawing, a plain QSGNode is created for
every possible Z-Value and items are added to these nodes.
Thus, items are rendered by Z-value and if the Z-value is equal
by order of creation.

Likewise split the list of chart-items into Z-values, so that
items can be quickly unregistered: The items that will be
removed individually will usuall be part of Z-levels with only
few items (e.g. legend, infobox). Z-levels with many items
(notably the series) will always be fully rebuilt.

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

1 files changed, 6 insertions, 5 deletions

diff --git a/stats/statsview.h b/stats/statsview.h
index 62fb246cd..1a922ac98 100644
--- a/stats/statsview.h
+++ b/stats/statsview.h
@@ -19,7 +19,6 @@ struct StatsVariable;
 
 class QGraphicsLineItem;
 class QGraphicsSimpleTextItem;
-class QSGImageNode;
 class StatsSeries;
 class CategoryAxis;
 class ChartItem;
@@ -29,8 +28,10 @@ class StatsAxis;
 class StatsGrid;
 class Legend;
 class QSGTexture;
+class RootNode;	// Internal implementation detail
 
 enum class ChartSubType : int;
+enum class ChartZValue : int;
 enum class StatsOperation : int;
 
 struct regression_data {
@@ -50,7 +51,8 @@ public:
 	void plot(const StatsState &state);
 	QQuickWindow *w() const;		// Make window available to items
 	QSizeF size() const;
-	void addQSGNode(QSGNode *node, int z);	// Must only be called in render thread!
+	void addQSGNode(QSGNode *node, ChartZValue z);	// Must only be called in render thread!
+	void registerChartItem(ChartItem *item);
 	void unregisterChartItem(const ChartItem *item);
 	template <typename T, class... Args>
 	std::unique_ptr<T> createChartItem(Args&&... args);
@@ -165,7 +167,6 @@ private:
 	std::vector<RegressionLine> regressionLines;
 	std::vector<HistogramMarker> histogramMarkers;
 	std::unique_ptr<QGraphicsSimpleTextItem> title;
-	std::vector<ChartItem *> items; // Attention: currently, items are not automatically removed on destruction!
 	StatsSeries *highlightedSeries;
 	StatsAxis *xAxis, *yAxis;
 	Legend *draggedItem;
@@ -176,7 +177,7 @@ private:
 	void mousePressEvent(QMouseEvent *event) override;
 	void mouseReleaseEvent(QMouseEvent *event) override;
 	void mouseMoveEvent(QMouseEvent *event) override;
-	QSGImageNode *rootNode;
+	RootNode *rootNode;
 };
 
 // This implementation detail must be known to users of the class.
@@ -185,7 +186,7 @@ template <typename T, class... Args>
 std::unique_ptr<T> StatsView::createChartItem(Args&&... args)
 {
 	std::unique_ptr<T> res(new T(*this, std::forward<Args>(args)...));
-	items.push_back(res.get());
+	registerChartItem(res.get());
 	return res;
 }