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>

2 files changed, 5 insertions, 0 deletions

diff --git a/backend-shared/roundrectitem.cpp b/backend-shared/roundrectitem.cpp
index 2dbfd7b03..52200b017 100644
--- a/backend-shared/roundrectitem.cpp
+++ b/backend-shared/roundrectitem.cpp
@@ -7,6 +7,10 @@ RoundRectItem::RoundRectItem(double radius, QGraphicsItem *parent) : QGraphicsRe
 {
 }
 
+RoundRectItem::RoundRectItem(double radius) : RoundRectItem(radius, nullptr)
+{
+}
+
 void RoundRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
 {
 	painter->save();
diff --git a/backend-shared/roundrectitem.h b/backend-shared/roundrectitem.h
index d3f58782f..b8cb3f89b 100644
--- a/backend-shared/roundrectitem.h
+++ b/backend-shared/roundrectitem.h
@@ -7,6 +7,7 @@
 class RoundRectItem : public QGraphicsRectItem {
 public:
 	RoundRectItem(double radius, QGraphicsItem *parent);
+	RoundRectItem(double radius);
 private:
 	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override;
 	double radius;