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, 32 insertions, 28 deletions

diff --git a/stats/statsaxis.cpp b/stats/statsaxis.cpp
index 019a16256..4d70488da 100644
--- a/stats/statsaxis.cpp
+++ b/stats/statsaxis.cpp
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "statsaxis.h"
 #include "statscolors.h"
+#include "statshelper.h"
 #include "statstranslations.h"
 #include "statsvariables.h"
 #include "zvalues.h"
@@ -23,9 +24,8 @@ static const double axisLabelSpaceVertical = 2.0;	// Space between axis or ticks
 static const double axisTitleSpaceHorizontal = 2.0;	// Space between labels and title
 static const double axisTitleSpaceVertical = 2.0;	// Space between labels and title
 
-StatsAxis::StatsAxis(QtCharts::QChart *chart, const QString &titleIn, bool horizontal, bool labelsBetweenTicks) :
-	QGraphicsLineItem(chart),
-	chart(chart), horizontal(horizontal), labelsBetweenTicks(labelsBetweenTicks),
+StatsAxis::StatsAxis(const QString &titleIn, bool horizontal, bool labelsBetweenTicks) :
+	horizontal(horizontal), labelsBetweenTicks(labelsBetweenTicks),
 	size(1.0), zeroOnScreen(0.0), min(0.0), max(1.0), labelWidth(0.0)
 {
 	// use a Light version of the application fond for both labels and title
@@ -35,7 +35,7 @@ StatsAxis::StatsAxis(QtCharts::QChart *chart, const QString &titleIn, bool horiz
 	setPen(QPen(axisColor, axisWidth));
 	setZValue(ZValues::axes);
 	if (!titleIn.isEmpty()) {
-		title = std::make_unique<QGraphicsSimpleTextItem>(titleIn, chart);
+		title.reset(new QGraphicsSimpleTextItem(titleIn, this));
 		title->setFont(titleFont);
 		title->setBrush(darkLabelColor);
 		if (!horizontal)
@@ -114,8 +114,8 @@ double StatsAxis::height() const
 	       (labelsBetweenTicks ? 0.0 : axisTickSizeHorizontal);
 }
 
-StatsAxis::Label::Label(const QString &name, double pos, QtCharts::QChart *chart, const QFont &font) :
-	label(new QGraphicsSimpleTextItem(name, chart)),
+StatsAxis::Label::Label(const QString &name, double pos, QGraphicsScene *scene, const QFont &font) :
+	label(createItem<QGraphicsSimpleTextItem>(scene, name)),
 	pos(pos)
 {
 	label->setBrush(QBrush(darkLabelColor));
@@ -125,11 +125,11 @@ StatsAxis::Label::Label(const QString &name, double pos, QtCharts::QChart *chart
 
 void StatsAxis::addLabel(const QString &label, double pos)
 {
-	labels.emplace_back(label, pos, chart, labelFont);
+	labels.emplace_back(label, pos, scene(), labelFont);
 }
 
-StatsAxis::Tick::Tick(double pos, QtCharts::QChart *chart) :
-	item(new QGraphicsLineItem(chart)),
+StatsAxis::Tick::Tick(double pos, QGraphicsScene *scene) :
+	item(createItemPtr<QGraphicsLineItem>(scene)),
 	pos(pos)
 {
 	item->setPen(QPen(axisColor, axisTickWidth));
@@ -138,7 +138,7 @@ StatsAxis::Tick::Tick(double pos, QtCharts::QChart *chart) :
 
 void StatsAxis::addTick(double pos)
 {
-	ticks.emplace_back(pos, chart);
+	ticks.emplace_back(pos, scene());
 }
 
 std::vector<double> StatsAxis::ticksPositions() const
@@ -220,8 +220,8 @@ void StatsAxis::setPos(QPointF pos)
 	}
 }
 
-ValueAxis::ValueAxis(QtCharts::QChart *chart, const QString &title, double min, double max, int decimals, bool horizontal) :
-	StatsAxis(chart, title, horizontal, false),
+ValueAxis::ValueAxis(const QString &title, double min, double max, int decimals, bool horizontal) :
+	StatsAxis(title, horizontal, false),
 	min(min), max(max), decimals(decimals)
 {
 }
@@ -275,8 +275,8 @@ void ValueAxis::updateLabels()
 	}
 }
 
-CountAxis::CountAxis(QtCharts::QChart *chart, const QString &title, int count, bool horizontal) :
-	ValueAxis(chart, title, 0.0, (double)count, 0, horizontal),
+CountAxis::CountAxis(const QString &title, int count, bool horizontal) :
+	ValueAxis(title, 0.0, (double)count, 0, horizontal),
 	count(count)
 {
 }
@@ -328,27 +328,31 @@ void CountAxis::updateLabels()
 	}
 }
 
-CategoryAxis::CategoryAxis(QtCharts::QChart *chart, const QString &title, const std::vector<QString> &labelsIn, bool horizontal) :
-	StatsAxis(chart, title, horizontal, true)
+CategoryAxis::CategoryAxis(const QString &title, const std::vector<QString> &labels, bool horizontal) :
+	StatsAxis(title, horizontal, true),
+	labelsText(labels)
 {
-	labels.reserve(labelsIn.size());
-	ticks.reserve(labelsIn.size() + 1);
+	setRange(-0.5, static_cast<double>(labels.size()) + 0.5);
+}
+
+void CategoryAxis::updateLabels()
+{
+	// TODO: paint ellipses if space too small
+	labels.clear();
+	ticks.clear();
+	labels.reserve(labelsText.size());
+	ticks.reserve(labelsText.size() + 1);
 	double pos = 0.0;
 	addTick(-0.5);
-	for (const QString &s: labelsIn) {
+	for (const QString &s: labelsText) {
 		addLabel(s, pos);
 		addTick(pos + 0.5);
 		pos += 1.0;
 	}
-	setRange(-0.5, static_cast<double>(labelsIn.size()) - 0.5);
-}
-
-void CategoryAxis::updateLabels()
-{
 }
 
-HistogramAxis::HistogramAxis(QtCharts::QChart *chart, const QString &title, std::vector<HistogramAxisEntry> bins, bool horizontal) :
-	StatsAxis(chart, title, horizontal, false),
+HistogramAxis::HistogramAxis(const QString &title, std::vector<HistogramAxisEntry> bins, bool horizontal) :
+	StatsAxis(title, horizontal, false),
 	bin_values(std::move(bins))
 {
 	if (bin_values.size() < 2) // Less than two makes no sense -> there must be at least one category
@@ -545,7 +549,7 @@ static std::vector<HistogramAxisEntry> timeRangeToBins(double from, double to)
 	return res;
 }
 
-DateAxis::DateAxis(QtCharts::QChart *chart, const QString &title, double from, double to, bool horizontal) :
-	HistogramAxis(chart, title, timeRangeToBins(from, to), horizontal)
+DateAxis::DateAxis(const QString &title, double from, double to, bool horizontal) :
+	HistogramAxis(title, timeRangeToBins(from, to), horizontal)
 {
 }