statistics: turn ChartGrid into QSGNodes

Turn the background grid into QSGNodes. Each grid line is
represented by a QSG line item. An alternative would be
drawing the grid into a QImage and blasting that onto the
screen. It is unclear which one is preferred.

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

3 files changed, 17 insertions, 19 deletions

diff --git a/stats/statsgrid.cpp b/stats/statsgrid.cpp
index 66c720c33..f8ad22c14 100644
--- a/stats/statsgrid.cpp
+++ b/stats/statsgrid.cpp
@@ -1,17 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "statsgrid.h"
+#include "chartitem.h"
 #include "statsaxis.h"
 #include "statscolors.h"
-#include "statshelper.h"
+#include "statsview.h"
 #include "zvalues.h"
 
-#include <QGraphicsLineItem>
-
 static const double gridWidth = 1.0;
-static const Qt::PenStyle gridStyle = Qt::SolidLine;
 
-StatsGrid::StatsGrid(QGraphicsScene *scene, const StatsAxis &xAxis, const StatsAxis &yAxis)
-	: scene(scene), xAxis(xAxis), yAxis(yAxis)
+StatsGrid::StatsGrid(StatsView &view, const StatsAxis &xAxis, const StatsAxis &yAxis)
+	: view(view), xAxis(xAxis), yAxis(yAxis)
 {
 }
 
@@ -19,18 +17,19 @@ void StatsGrid::updatePositions()
 {
 	std::vector<double> xtics = xAxis.ticksPositions();
 	std::vector<double> ytics = yAxis.ticksPositions();
+
+	// We probably should be smarter and reuse existing lines.
+	// For now, this does it.
 	lines.clear();
 	if (xtics.empty() || ytics.empty())
 		return;
 
 	for (double x: xtics) {
-		lines.emplace_back(createItem<QGraphicsLineItem>(scene, x, ytics.front(), x, ytics.back()));
-		lines.back()->setPen(QPen(gridColor, gridWidth, gridStyle));
-		lines.back()->setZValue(ZValues::grid);
+		lines.push_back(view.createChartItem<ChartLineItem>(ChartZValue::Grid, gridColor, gridWidth));
+		lines.back()->setLine(QPointF(x, ytics.front()), QPointF(x, ytics.back()));
 	}
 	for (double y: ytics) {
-		lines.emplace_back(createItem<QGraphicsLineItem>(scene, xtics.front(), y, xtics.back(), y));
-		lines.back()->setPen(QPen(gridColor, gridWidth, gridStyle));
-		lines.back()->setZValue(ZValues::grid);
+		lines.push_back(view.createChartItem<ChartLineItem>(ChartZValue::Grid, gridColor, gridWidth));
+		lines.back()->setLine(QPointF(xtics.front(), y), QPointF(xtics.back(), y));
 	}
 }
diff --git a/stats/statsgrid.h b/stats/statsgrid.h
index 47b48b3ac..ab1b0a513 100644
--- a/stats/statsgrid.h
+++ b/stats/statsgrid.h
@@ -3,18 +3,17 @@
 
 #include <memory>
 #include <vector>
-#include <QVector>
-#include <QGraphicsLineItem>
 
 class StatsAxis;
-class QGraphicsScene;
+class StatsView;
+class ChartLineItem;
 
 class StatsGrid  {
 public:
-	StatsGrid(QGraphicsScene *scene, const StatsAxis &xAxis, const StatsAxis &yAxis);
+	StatsGrid(StatsView &view, const StatsAxis &xAxis, const StatsAxis &yAxis);
 	void updatePositions();
 private:
-	QGraphicsScene *scene;
+	StatsView &view;
 	const StatsAxis &xAxis, &yAxis;
-	std::vector<std::unique_ptr<QGraphicsLineItem>> lines;
+	std::vector<std::unique_ptr<ChartLineItem>> lines;
 };
diff --git a/stats/statsview.cpp b/stats/statsview.cpp
index 29ee2d990..83a586456 100644
--- a/stats/statsview.cpp
+++ b/stats/statsview.cpp
@@ -317,7 +317,7 @@ void StatsView::setAxes(StatsAxis *x, StatsAxis *y)
 	xAxis = x;
 	yAxis = y;
 	if (x && y)
-		grid = std::make_unique<StatsGrid>(&scene, *x, *y);
+		grid = std::make_unique<StatsGrid>(*this, *x, *y);
 }
 
 void StatsView::reset()