From e7907c494f7f78831c2e2d523f7eb43e25ee77c0 Mon Sep 17 00:00:00 2001
From: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
Date: Thu, 7 Jan 2021 14:38:37 +0100
Subject: 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>
---
 stats/statsaxis.h | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

(limited to 'stats/statsaxis.h')

diff --git a/stats/statsaxis.h b/stats/statsaxis.h
index d9fdd6b41..dbcfb6fbd 100644
--- a/stats/statsaxis.h
+++ b/stats/statsaxis.h
@@ -11,11 +11,9 @@
 #include <QGraphicsLineItem>
 #include <QValueAxis>
 
-namespace QtCharts {
-	class QChart;
-}
+class QGraphicsScene;
 
-class StatsAxis : QGraphicsLineItem {
+class StatsAxis : public QGraphicsLineItem {
 public:
 	virtual ~StatsAxis();
 	// Returns minimum and maximum of shown range, not of data points.
@@ -34,13 +32,12 @@ public:
 
 	std::vector<double> ticksPositions() const; // Positions in screen coordinates
 protected:
-	StatsAxis(QtCharts::QChart *chart, const QString &title, bool horizontal, bool labelsBetweenTicks);
-	QtCharts::QChart *chart;
+	StatsAxis(const QString &title, bool horizontal, bool labelsBetweenTicks);
 
 	struct Label {
 		std::unique_ptr<QGraphicsSimpleTextItem> label;
 		double pos;
-		Label(const QString &name, double pos, QtCharts::QChart *chart, const QFont &font);
+		Label(const QString &name, double pos, QGraphicsScene *scene, const QFont &font);
 	};
 	std::vector<Label> labels;
 	void addLabel(const QString &label, double pos);
@@ -49,7 +46,7 @@ protected:
 	struct Tick {
 		std::unique_ptr<QGraphicsLineItem> item;
 		double pos;
-		Tick(double pos, QtCharts::QChart *chart);
+		Tick(double pos, QGraphicsScene *scene);
 	};
 	std::vector<Tick> ticks;
 	void addTick(double pos);
@@ -70,7 +67,7 @@ private:
 
 class ValueAxis : public StatsAxis {
 public:
-	ValueAxis(QtCharts::QChart *chart, const QString &title, double min, double max, int decimals, bool horizontal);
+	ValueAxis(const QString &title, double min, double max, int decimals, bool horizontal);
 private:
 	double min, max;
 	int decimals;
@@ -79,7 +76,7 @@ private:
 
 class CountAxis : public ValueAxis {
 public:
-	CountAxis(QtCharts::QChart *chart, const QString &title, int count, bool horizontal);
+	CountAxis(const QString &title, int count, bool horizontal);
 private:
 	int count;
 	void updateLabels() override;
@@ -87,8 +84,9 @@ private:
 
 class CategoryAxis : public StatsAxis {
 public:
-	CategoryAxis(QtCharts::QChart *chart, const QString &title, const std::vector<QString> &labels, bool horizontal);
+	CategoryAxis(const QString &title, const std::vector<QString> &labels, bool horizontal);
 private:
+	std::vector<QString> labelsText;
 	void updateLabels();
 };
 
@@ -100,7 +98,7 @@ struct HistogramAxisEntry {
 
 class HistogramAxis : public StatsAxis {
 public:
-	HistogramAxis(QtCharts::QChart *chart, const QString &title, std::vector<HistogramAxisEntry> bin_values, bool horizontal);
+	HistogramAxis(const QString &title, std::vector<HistogramAxisEntry> bin_values, bool horizontal);
 private:
 	void updateLabels() override;
 	std::vector<HistogramAxisEntry> bin_values;
@@ -109,7 +107,7 @@ private:
 
 class DateAxis : public HistogramAxis {
 public:
-	DateAxis(QtCharts::QChart *chart, const QString &title, double from, double to, bool horizontal);
+	DateAxis(const QString &title, double from, double to, bool horizontal);
 };
 
 #endif
-- 
cgit v1.2.3-70-g09d2