statistics: fix chart features: regression line and median/mean

The coordinates of these were calculated when creating the feature.
This is wrong, because the min/max values of the axes can change
on resize to get "nice" number. Therefore, recalculate after resizing.
This means that the general "LineMarker" class has to be split into
two classes, one for regression lines and one for median/mean
markers.

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

stats/statsaxis.cpp

@@ -52,6 +52,12 @@ std::pair<double, double> StatsAxis::minMax() const
 	return { min, max };
 }
 
+std::pair<double, double> StatsAxis::minMaxScreen() const
+{
+	return horizontal ? std::make_pair(zeroOnScreen, zeroOnScreen + size)
+			  : std::make_pair(zeroOnScreen, zeroOnScreen - size);
+}
+
 void StatsAxis::setRange(double minIn, double maxIn)
 {
 	min = minIn;

stats/statsaxis.h

@@ -20,6 +20,7 @@ public:
 	virtual ~StatsAxis();
 	// Returns minimum and maximum of shown range, not of data points.
 	std::pair<double, double> minMax() const;
+	std::pair<double, double> minMaxScreen() const; // minimum and maximum in screen coordinates
 
 	double width() const;		// Only supported by vertical axes. Only valid after setSize().
 	double height() const;		// Only supported for horizontal axes. Always valid.

stats/statsview.cpp

@@ -125,7 +125,9 @@ void StatsView::plotAreaChanged(const QRectF &r)
 		series->updatePositions();
 	for (QuartileMarker &marker: quartileMarkers)
 		marker.updatePosition();
-	for (LineMarker &marker: lineMarkers)
+	for (RegressionLine &line: regressionLines)
+		line.updatePosition();
+	for (HistogramMarker &marker: histogramMarkers)
 		marker.updatePosition();
 	if (legend)
 		legend->resize();
@@ -211,7 +213,8 @@ void StatsView::reset()
 	legend.reset();
 	series.clear();
 	quartileMarkers.clear();
-	lineMarkers.clear();
+	regressionLines.clear();
+	histogramMarkers.clear();
 	chart->removeAllSeries();
 	grid.reset();
 	axes.clear();
@@ -716,37 +719,25 @@ void StatsView::QuartileMarker::updatePosition()
 		      x + quartileMarkerSize / 2.0, y);
 }
 
-StatsView::LineMarker::LineMarker(QPointF from, QPointF to, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
+StatsView::RegressionLine::RegressionLine(double a, double b, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
 	item(new QGraphicsLineItem(chart)),
 	xAxis(xAxis), yAxis(yAxis),
-	from(from), to(to)
+	a(a), b(b)
 {
 	item->setZValue(ZValues::chartFeatures);
 	item->setPen(pen);
-	updatePosition();
 }
 
-void StatsView::LineMarker::updatePosition()
+void StatsView::RegressionLine::updatePosition()
 {
 	if (!xAxis || !yAxis)
 		return;
-	double x1 = xAxis->toScreen(from.x());
+	auto [minX, maxX] = xAxis->minMax();
-	double y1 = yAxis->toScreen(from.y());
+	auto [minY, maxY] = yAxis->minMax();
-	double x2 = xAxis->toScreen(to.x());
-	double y2 = yAxis->toScreen(to.y());
-	item->setLine(x1, y1, x2, y2);
-}
-
-void StatsView::addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis)
-{
-	// Sanity check: line above or below chart
 	double y1 = a * minX + b;
 	double y2 = a * maxX + b;
-	if ((y1 <= minY && y2 <= minY) || (y1 >= maxY && y2 >= maxY))
-		return;
 
-	// If not fully inside drawing region, do clipping. With the check above this guarantees that a != 0,
+	// If not fully inside drawing region, do clipping.
-	// but owing to floating point imprecision, let's test again.
 	if ((y1 < minY || y1 > maxY || y2 < minY || y2 > maxY) && fabs(a) > 0.0001) {
 		// Intersections with y = minY and y = maxY lines
 		double intersect_x1 = (minY - b) / a;
@@ -756,14 +747,42 @@ void StatsView::addLinearRegression(double a, double b, double minX, double maxX
 		minX = std::max(minX, intersect_x1);
 		maxX = std::min(maxX, intersect_x2);
 	}
-	lineMarkers.emplace_back(QPointF(minX, a * minX + b), QPointF(maxX, a * maxX + b), QPen(Qt::red), chart, xAxis, yAxis);
+	item->setLine(xAxis->toScreen(minX), yAxis->toScreen(a * minX + b),
+		      xAxis->toScreen(maxX), yAxis->toScreen(a * maxX + b));
 }
 
-void StatsView::addHistogramMarker(double pos, double low, double high, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis)
+StatsView::HistogramMarker::HistogramMarker(double val, bool horizontal, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis) :
+	item(new QGraphicsLineItem(chart)),
+	xAxis(xAxis), yAxis(yAxis),
+	val(val), horizontal(horizontal)
 {
-	QPointF from = isHorizontal ? QPointF(low, pos) : QPointF(pos, low);
+	item->setZValue(ZValues::chartFeatures);
-	QPointF to = isHorizontal ? QPointF(high, pos) : QPointF(pos, high);
+	item->setPen(pen);
-	lineMarkers.emplace_back(from, to, pen, chart, xAxis, yAxis);
+}
+
+void StatsView::HistogramMarker::updatePosition()
+{
+	if (!xAxis || !yAxis)
+		return;
+	if (horizontal) {
+		double y = yAxis->toScreen(val);
+		auto [x1, x2] = xAxis->minMaxScreen();
+		item->setLine(x1, y, x2, y);
+	} else {
+		double x = xAxis->toScreen(val);
+		auto [y1, y2] = yAxis->minMaxScreen();
+		item->setLine(x, y1, x, y2);
+	}
+}
+
+void StatsView::addHistogramMarker(double pos, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis)
+{
+	histogramMarkers.emplace_back(pos, isHorizontal, pen, chart, xAxis, yAxis);
+}
+
+void StatsView::addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis)
+{
+	regressionLines.emplace_back(a, b, QPen(Qt::red), chart, xAxis, yAxis);
 }
 
 // Yikes, we get our data in different kinds of (bin, value) pairs.
@@ -812,7 +831,6 @@ void StatsView::plotHistogramCountChart(const std::vector<dive *> &dives,
 	int total = getTotalCount(categoryBins);
 
 	StatsAxis *valAxis = createCountAxis(maxCategoryCount, isHorizontal);
-	double chartHeight = valAxis->minMax().second;
 
 	if (isHorizontal)
 		setAxes(valAxis, catAxis);
@@ -840,14 +858,14 @@ void StatsView::plotHistogramCountChart(const std::vector<dive *> &dives,
 			QPen meanPen(Qt::green);
 			meanPen.setWidth(2);
 			if (!std::isnan(mean))
-				addHistogramMarker(mean, 0.0, chartHeight, meanPen, isHorizontal, xAxis, yAxis);
+				addHistogramMarker(mean, meanPen, isHorizontal, xAxis, yAxis);
 		}
 		if (showMedian) {
 			double median = categoryVariable->quartiles(dives).q2;
 			QPen medianPen(Qt::red);
 			medianPen.setWidth(2);
 			if (!std::isnan(median))
-				addHistogramMarker(median, 0.0, chartHeight, medianPen, isHorizontal, xAxis, yAxis);
+				addHistogramMarker(median, medianPen, isHorizontal, xAxis, yAxis);
 		}
 	}
 }

stats/statsview.h

@@ -106,17 +106,27 @@ private:
 		void updatePosition();
 	};
 
-	// A general line marker
+	// A regression line
-	struct LineMarker {
+	struct RegressionLine {
 		std::unique_ptr<QGraphicsLineItem> item;
 		StatsAxis *xAxis, *yAxis;
-		QPointF from, to; // In local coordinates
+		double a, b;			// y = ax + b
 		void updatePosition();
-		LineMarker(QPointF from, QPointF to, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
+		RegressionLine(double a, double b, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
+	};
+
+	// A line marking median or mean in histograms
+	struct HistogramMarker {
+		std::unique_ptr<QGraphicsLineItem> item;
+		StatsAxis *xAxis, *yAxis;
+		double val;
+		bool horizontal;
+		void updatePosition();
+		HistogramMarker(double val, bool horizontal, QPen pen, QtCharts::QChart *chart, StatsAxis *xAxis, StatsAxis *yAxis);
 	};
 
 	void addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis);
-	void addHistogramMarker(double pos, double low, double high, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis);
+	void addHistogramMarker(double pos, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis);
 
 	StatsState state;
 	QtCharts::QChart *chart;
@@ -126,7 +136,8 @@ private:
 	std::vector<std::unique_ptr<StatsSeries>> series;
 	std::unique_ptr<Legend> legend;
 	std::vector<QuartileMarker> quartileMarkers;
-	std::vector<LineMarker> lineMarkers;
+	std::vector<RegressionLine> regressionLines;
+	std::vector<HistogramMarker> histogramMarkers;
 	std::unique_ptr<QGraphicsSimpleTextItem> title;
 	StatsSeries *highlightedSeries;
 	StatsAxis *xAxis, *yAxis;