ui: Fixed exporting images from the graph resulted in too large images (issue #511)

* Fixed style issue in save dialog on Linux
* Fixed wrong dialog used on Mac and Windows
* Improved image quality

bug id = 511

src/lib_gui/qt/graphics/QtGraphicsView.cpp

@@ -92,6 +92,13 @@ void QtGraphicsView::setAppZoomFactor(float appZoomFactor)
 	updateTransform();
 }
 
+void QtGraphicsView::setSceneRect(const QRectF& rect)
+{
+	QGraphicsView::setSceneRect(rect);
+
+	scene()->setSceneRect(rect);
+}
+
 QtGraphNode* QtGraphicsView::getNodeAtCursorPosition() const
 {
 	QtGraphNode* node = nullptr;
@@ -409,11 +416,11 @@ void QtGraphicsView::stopTimer()
 void QtGraphicsView::exportGraph()
 {
 	QString fileName = QtFileDialog::showSaveFileDialog(
-		this, "Save image", QDir::homePath(), "PNG (*.png);;JPEG (*.JPEG);;BMP Files (*.bmp)");
+		nullptr, "Save image", QDir::homePath(), "PNG (*.png);;JPEG (*.JPEG);;BMP Files (*.bmp)");
 
 	if (!fileName.isNull())
 	{
-		QImage image(scene()->sceneRect().size().toSize(), QImage::Format_ARGB32);
+		QImage image(scene()->sceneRect().size().toSize() * 2, QImage::Format_ARGB32);
 		image.fill(Qt::transparent);
 
 		QPainter painter(&image);
@@ -421,7 +428,7 @@ void QtGraphicsView::exportGraph()
 		scene()->render(&painter);
 		image.save(fileName);
 
-		// different approach
+		// different approach: only currently visible part
 		// QPixmap pixMap = grab();
 		// pixMap.save(fileName);
 	}

src/lib_gui/qt/graphics/QtGraphicsView.h

@@ -22,6 +22,8 @@ public:
 	float getZoomFactor() const;
 	void setAppZoomFactor(float appZoomFactor);
 
+	void setSceneRect(const QRectF& rect);
+
 	QtGraphNode* getNodeAtCursorPosition() const;
 
 	void ensureVisibleAnimated(const QRectF& rect, int xmargin = 50, int ymargin = 50);

src/lib_gui/qt/utility/QtFileDialog.cpp

@@ -51,7 +51,7 @@ QString QtFileDialog::getOpenFileName(QWidget* parent, const QString& caption, c
 QString QtFileDialog::showSaveFileDialog(
 	QWidget *parent, const QString& title, const QString& directory, const QString& filter)
 {
-#if defined(Q_WS_WIN) || defined(Q_WS_MAC)
+#if defined(Q_OS_WIN) || defined(Q_OS_MAC)
 
 	return QFileDialog::getSaveFileName(parent, title, directory, filter);
 
@@ -92,7 +92,7 @@ QString QtFileDialog::showSaveFileDialog(
 	{
 		return QString();
 	}
-#endif  // Q_WS_MAC || Q_WS_WIN
+#endif  // Q_OS_MAC || Q_OS_WIN
 }
 
 QString QtFileDialog::getDir(QString dir)