statistics: paint custom grid

With removal of QtCharts' axes, the grid was lost. Readd it.

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

stats/CMakeLists.txt

@@ -23,6 +23,8 @@ set(SUBSURFACE_STATS_SRCS
 	statsaxis.cpp
 	statscolors.h
 	statscolors.cpp
+	statsgrid.h
+	statsgrid.cpp
 	statsseries.h
 	statsseries.cpp
 	statsstate.h

stats/statsaxis.cpp

@@ -135,6 +135,15 @@ void StatsAxis::addTick(double pos)
 	ticks.emplace_back(pos, chart);
 }
 
+std::vector<double> StatsAxis::ticksPositions() const
+{
+	std::vector<double> res;
+	res.reserve(ticks.size());
+	for (const Tick &tick: ticks)
+		res.push_back(toScreen(tick.pos));
+	return res;
+}
+
 // Map x (horizontal) or y (vertical) coordinate to or from screen coordinate
 double StatsAxis::toScreen(double pos) const
 {

stats/statsaxis.h

@@ -30,6 +30,8 @@ public:
 	// Map x (horizontal) or y (vertical) coordinate to or from screen coordinate
 	double toScreen(double) const;
 	double toValue(double) const;
+
+	std::vector<double> ticksPositions() const; // Positions in screen coordinates
 protected:
 	StatsAxis(QtCharts::QChart *chart, const QString &title, bool horizontal, bool labelsBetweenTicks);
 	QtCharts::QChart *chart;

stats/statscolors.h

@@ -12,6 +12,7 @@ inline const QColor highlightedBorderColor(0xaa, 0xaa, 0x22);
 inline const QColor darkLabelColor(Qt::black);
 inline const QColor lightLabelColor(Qt::white);
 inline const QColor axisColor(Qt::black);
+inline const QColor gridColor(0xcc, 0xcc, 0xcc);
 
 QColor binColor(int bin, int numBins);
 QColor labelColor(int bin, size_t numBins);

stats/statsgrid.cpp

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "statsgrid.h"
+#include "statsaxis.h"
+#include "statscolors.h"
+#include "zvalues.h"
+
+#include <QChart>
+#include <QGraphicsLineItem>
+
+static const double gridWidth = 1.0;
+static const Qt::PenStyle gridStyle = Qt::SolidLine;
+
+StatsGrid::StatsGrid(QtCharts::QChart *chart, const StatsAxis &xAxis, const StatsAxis &yAxis)
+	: chart(chart), xAxis(xAxis), yAxis(yAxis)
+{
+}
+
+void StatsGrid::updatePositions()
+{
+	std::vector<double> xtics = xAxis.ticksPositions();
+	std::vector<double> ytics = yAxis.ticksPositions();
+	lines.clear();
+	if (xtics.empty() || ytics.empty())
+		return;
+
+	for (double x: xtics) {
+		lines.emplace_back(new QGraphicsLineItem(x, ytics.front(), x, ytics.back(), chart));
+		lines.back()->setPen(QPen(gridColor, gridWidth, gridStyle));
+		lines.back()->setZValue(ZValues::grid);
+	}
+	for (double y: ytics) {
+		lines.emplace_back(new QGraphicsLineItem(xtics.front(), y, xtics.back(), y, chart));
+		lines.back()->setPen(QPen(gridColor, gridWidth, gridStyle));
+		lines.back()->setZValue(ZValues::grid);
+	}
+}

stats/statsgrid.h

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// The background grid of a chart
+
+#include <memory>
+#include <vector>
+#include <QVector>
+#include <QGraphicsLineItem>
+
+class StatsAxis;
+namespace QtCharts {
+	class QChart;
+};
+
+class StatsGrid  {
+public:
+	StatsGrid(QtCharts::QChart *chart, const StatsAxis &xAxis, const StatsAxis &yAxis);
+	void updatePositions();
+private:
+	QtCharts::QChart *chart;
+	const StatsAxis &xAxis, &yAxis;
+	std::vector<std::unique_ptr<QGraphicsLineItem>> lines;
+};

stats/statsview.cpp

@@ -6,6 +6,7 @@
 #include "pieseries.h"
 #include "scatterseries.h"
 #include "statsaxis.h"
+#include "statsgrid.h"
 #include "statsstate.h"
 #include "statstranslations.h"
 #include "statsvariables.h"
@@ -118,6 +119,8 @@ void StatsView::plotAreaChanged(const QRectF &r)
 		xAxis->setPos(QPointF(left, bottom));
 	}
 
+	if (grid)
+		grid->updatePositions();
 	for (auto &series: series)
 		series->updatePositions();
 	for (QuartileMarker &marker: quartileMarkers)
@@ -195,6 +198,8 @@ void StatsView::setAxes(StatsAxis *x, StatsAxis *y)
 {
 	xAxis = x;
 	yAxis = y;
+	if (x && y)
+		grid = std::make_unique<StatsGrid>(chart, *x, *y);
 }
 
 void StatsView::reset()
@@ -208,6 +213,7 @@ void StatsView::reset()
 	quartileMarkers.clear();
 	lineMarkers.clear();
 	chart->removeAllSeries();
+	grid.reset();
 	axes.clear();
 	title.reset();
 }

stats/statsview.h

@@ -24,6 +24,7 @@ class CategoryAxis;
 class CountAxis;
 class HistogramAxis;
 class StatsAxis;
+class StatsGrid;
 class Legend;
 
 enum class ChartSubType : int;
@@ -121,6 +122,7 @@ private:
 	QtCharts::QChart *chart;
 	QFont titleFont;
 	std::vector<std::unique_ptr<StatsAxis>> axes;
+	std::unique_ptr<StatsGrid> grid;
 	std::vector<std::unique_ptr<StatsSeries>> series;
 	std::unique_ptr<Legend> legend;
 	std::vector<QuartileMarker> quartileMarkers;

stats/zvalues.h

@@ -6,6 +6,7 @@
 #ifndef ZVALUES_H
 
 struct ZValues {
+	static constexpr double grid = -1.0;
 	static constexpr double series = 0.0;
 	static constexpr double axes = 1.0;
 	static constexpr double seriesLabels = 2.0;