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, 4 insertions, 2 deletions

diff --git a/stats/chartitem.h b/stats/chartitem.h
index fb4b67dff..8cb9ef3a7 100644
--- a/stats/chartitem.h
+++ b/stats/chartitem.h
@@ -10,10 +10,11 @@
 class QSGImageNode;
 class QSGTexture;
 class StatsView;
+enum class ChartZValue : int;
 
 class ChartItem {
 public:
-	ChartItem(StatsView &v);
+	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*.
@@ -21,6 +22,7 @@ public:
 	void render();			// Only call on render thread!
 	QRectF getRect() const;
 	bool dirty;			// If true, call render() when rebuilding the scene
+	const ChartZValue zValue;
 protected:
 	std::unique_ptr<QPainter> painter;
 	std::unique_ptr<QImage> img;
@@ -39,7 +41,7 @@ private:
 // Draw a rectangular background after resize. Children are responsible for calling update().
 class ChartRectItem : public ChartItem {
 public:
-	ChartRectItem(StatsView &v, const QPen &pen, const QBrush &brush, double radius);
+	ChartRectItem(StatsView &v, ChartZValue z, const QPen &pen, const QBrush &brush, double radius);
 	~ChartRectItem();
 	void resize(QSizeF size);
 private: