statistics: convert chart to QQuickItem

It turns out that the wrong base class was used for the chart.
QQuickWidget can only be used on desktop, not in a mobile UI.

Therefore, turn this into a QQuickItem and move the container
QQuickWidget into desktop-only code.

Currently, this code is insane: The chart is rendered onto a
QGraphicsScene (as it was before), which is then rendered into
a QImage, which is transformed into a QSGTexture, which is then
projected onto the device. This is performed on every mouse
move event, since these events in general change the position
of the info-box.

The plan is to slowly convert elements such as the info-box into
QQuickItems. Browsing the QtQuick documentation, this will
not be much fun.

Also note that the rendering currently tears, flickers and has
antialiasing artifacts, most likely owing to integer (QImage)
to floating point (QGraphicsScene, QQuickItem) conversion
problems. The data flow is
QGraphicsScene (float) -> QImage (int) -> QQuickItem (float).

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

1 files changed, 2 insertions, 2 deletions

diff --git a/stats/legend.h b/stats/legend.h
index 2baf6f67b..c643a41f3 100644
--- a/stats/legend.h
+++ b/stats/legend.h
@@ -8,11 +8,12 @@
 #include <memory>
 #include <vector>
 
+class QGraphicsScene;
 class QGraphicsSceneMouseEvent;
 
 class Legend : public RoundRectItem {
 public:
-	Legend(QGraphicsWidget *chart, const std::vector<QString> &names);
+	Legend(const std::vector<QString> &names);
 	void hover(QPointF pos);
 	void resize(); // called when the chart size changes.
 private:
@@ -24,7 +25,6 @@ private:
 		double width;
 		Entry(const QString &name, int idx, int numBins, QGraphicsItem *parent);
 	};
-	QGraphicsWidget *chart;
 	int displayedItems;
 	double width;
 	double height;