statistics: draw background using a QSGRectangle node

Currently, the background was drawn as solid color onto
the chart-scene. This is of course incompatible with doing
the grid as QSGNodes. Therefore, make the scene image
transparent and use a QSGRectangle as background color.

We could also simply omit the background and show the
widget's background. However, that would mean setting
the background color in two seperate code paths
(desktop and mobile). I found no way of directly setting
the background of the QQuickItem.

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

1 files changed, 19 insertions, 10 deletions

diff --git a/stats/statsview.cpp b/stats/statsview.cpp
index 1e09a8cc5..29ee2d990 100644
--- a/stats/statsview.cpp
+++ b/stats/statsview.cpp
@@ -24,6 +24,7 @@
 #include <QQuickItem>
 #include <QQuickWindow>
 #include <QSGImageNode>
+#include <QSGRectangleNode>
 #include <QSGTexture>
 
 // Constants that control the graph layouts
@@ -83,19 +84,29 @@ void StatsView::mouseReleaseEvent(QMouseEvent *)
 class RootNode : public QSGNode
 {
 public:
-	RootNode();
+	RootNode(QQuickWindow *w);
+	QSGRectangleNode *backgroundNode; // solid background
 	QSGImageNode *imageNode; // imageNode to plot QGRaphicsScene on. Remove in due course.
 	// We entertain one node per Z-level.
 	std::array<QSGNode *, (size_t)ChartZValue::Count> zNodes;
 	std::array<std::vector<ChartItem *>, (size_t)ChartZValue::Count> items;
 };
 
-RootNode::RootNode()
+RootNode::RootNode(QQuickWindow *w)
 {
+	// Add a background rectangle with a solid color. This could
+	// also be done on the widget level, but would have to be done
+	// separately for desktop and mobile, so do it here.
+	backgroundNode = w->createRectangleNode();
+	backgroundNode->setColor(backgroundColor);
+	appendChildNode(backgroundNode);
+
 	for (QSGNode *&zNode: zNodes) {
 		zNode = new QSGNode;
 		appendChildNode(zNode);
 	}
+	imageNode = w->createImageNode();
+	zNodes[(int)ChartZValue::Series]->appendChildNode(imageNode);
 }
 
 QSGNode *StatsView::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *)
@@ -103,15 +114,13 @@ QSGNode *StatsView::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNod
 	// The QtQuick drawing interface is utterly bizzare with a distinct 1980ies-style memory management.
 	// This is just a copy of what is found in Qt's documentation.
 	RootNode *n = static_cast<RootNode *>(oldNode);
-	if (!n) {
-		n = rootNode = new RootNode;
-		n->imageNode = window()->createImageNode();
-		n->zNodes[(int)ChartZValue::Series]->appendChildNode(n->imageNode);
-	}
+	if (!n)
+		n = rootNode = new RootNode(window());
 
 	QRectF rect = boundingRect();
 	if (plotRect != rect) {
 		plotRect = rect;
+		rootNode->backgroundNode->setRect(rect);
 		plotAreaChanged(plotRect.size());
 	}
 
@@ -122,9 +131,9 @@ QSGNode *StatsView::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNod
 		}
 	}
 
-	img->fill(backgroundColor);
+	img->fill(Qt::transparent);
 	scene.render(painter.get());
-	texture.reset(window()->createTextureFromImage(*img, QQuickWindow::TextureIsOpaque));
+	texture.reset(window()->createTextureFromImage(*img, QQuickWindow::TextureHasAlphaChannel));
 	n->imageNode->setTexture(texture.get());
 	n->imageNode->setRect(rect);
 	return n;
@@ -172,7 +181,7 @@ void StatsView::plotAreaChanged(const QSizeF &s)
 	int h = std::max(1, static_cast<int>(floor(s.height())));
 	scene.setSceneRect(QRectF(0, 0, static_cast<double>(w), static_cast<double>(h)));
 	painter.reset();
-	img.reset(new QImage(w, h, QImage::Format_RGB32));
+	img.reset(new QImage(w, h, QImage::Format_ARGB32));
 	painter.reset(new QPainter(img.get()));
 	painter->setRenderHint(QPainter::Antialiasing);