Avoid showing a separate-window tooltip

data/gui/normalStyle.css

@@ -32,11 +32,13 @@ QFrame[frameShape="5"] { /* QFrame::VLine == 0x0005 */
         border: 1px solid rgb(31, 31, 31);
 }
 
+#StelToolTip,
 QToolTip {
 	color: rgb(4, 5, 9);
 	font-size: 100%;
 	padding: 2px;
 	background: rgb(143, 143, 143);
+	border: 1px solid rgb(0, 0, 0);
 }
 
 *[nightMode="true"] QToolTip {

src/StelMainView.cpp

@@ -41,6 +41,7 @@
 #include <QGuiApplication>
 #include <QGraphicsSceneMouseEvent>
 #include <QGraphicsAnchorLayout>
+#include <QGraphicsProxyWidget>
 #include <QGraphicsWidget>
 #include <QGraphicsEffect>
 #include <QFileInfo>
@@ -349,6 +350,47 @@ class StelGraphicsScene : public QGraphicsScene
 		//pass event on to items otherwise
 		QGraphicsScene::keyPressEvent(event);
 	}
+	void helpEvent(QGraphicsSceneHelpEvent* event) override
+	{
+		const QPoint pos(parent->mapFromGlobal(event->screenPos()));
+		QList<QGraphicsItem*> itemsToCheck;
+		if (parent->isTransformed())
+		{
+			const auto xform = parent->viewportTransform();
+			itemsToCheck = items(xform.inverted().map(pos), Qt::IntersectsItemShape,
+			                     Qt::DescendingOrder, xform);
+		}
+		else
+		{
+			itemsToCheck = items(pos, Qt::IntersectsItemShape, Qt::DescendingOrder);
+		}
+		QString text;
+		QPoint point;
+		for (auto*const item : itemsToCheck)
+		{
+			if (const auto proxy = dynamic_cast<QGraphicsProxyWidget*>(item))
+			{
+				const auto itemWidget = proxy->widget();
+				if (!itemWidget) continue;
+				const auto child = itemWidget->childAt(pos);
+				if (child && !child->toolTip().isEmpty())
+				{
+					text = child->toolTip();
+					point = pos;
+					break;
+				}
+			}
+			if (!item->toolTip().isEmpty())
+			{
+				text = item->toolTip();
+				point = pos;
+				break;
+			}
+		}
+
+		parent->showToolTip(point, text);
+		event->setAccepted(!text.isEmpty());
+	}
 
 private:
 	StelMainView* parent;
@@ -1990,6 +2032,11 @@ Vec3f StelMainView::getSkyBackgroundColor() const
 	return rootItem->getSkyBackgroundColor();
 }
 
+void StelMainView::showToolTip(const QPoint& scenePos, const QString& text)
+{
+	gui->showToolTip(scenePos, text);
+}
+
 QRectF StelMainView::setWindowSize(int width, int height)
 {
 	// Make sure to leave fullscreen if necessary.

src/StelMainView.hpp

@@ -232,6 +232,8 @@ public slots:
 	//! Get the sky background color. (Actually retrieves from the StelRootItem.)  Everything else than black creates a work of art!
 	Vec3f getSkyBackgroundColor() const;
 
+	void showToolTip(const QPoint& scenePos, const QString& text);
+
 protected:
 	//! Hack to determine current monitor pixel ratio
 	//! @todo Find a better way to handle this

src/core/StelGuiBase.hpp

@@ -35,6 +35,8 @@ class StelGuiBase
 
 	virtual void init(QGraphicsWidget *atopLevelGraphicsWidget);
 
+	virtual void showToolTip(const QPoint& scenePos, const QString& text) = 0;
+
 	//! Load color scheme matching the section name.
 	virtual void setStelStyle(const QString& section) =0;
 

src/gui/StelGui.cpp

@@ -238,6 +238,8 @@ void StelGui::init(QGraphicsWidget *atopLevelGraphicsWidget)
 	astroCalcDialog = new AstroCalcDialog(atopLevelGraphicsWidget);
 	obsListDialog = new ObsListDialog(atopLevelGraphicsWidget);
 
+	toolTip = new StelToolTip(atopLevelGraphicsWidget);
+
 	///////////////////////////////////////////////////////////////////////
 	// Create all the main actions of the program, associated with shortcuts
 
@@ -646,6 +648,11 @@ void StelGui::update()
 	}
 }
 
+void StelGui::showToolTip(const QPoint& scenePos, const QString& text)
+{
+	toolTip->showToolTip(scenePos, text);
+}
+
 void StelGui::displayAllInfo()
 {
 	setInfoTextFilters(StelObject::InfoStringGroup(StelObject::AllInfo));

src/gui/StelGui.hpp

@@ -32,6 +32,7 @@
 class QGraphicsSceneMouseEvent;
 class QTimeLine;
 class StelButton;
+class StelToolTip;
 class BottomStelBar;
 class InfoPanel;
 class ConfigurationDialog;
@@ -90,6 +91,8 @@ class StelGui : public QObject, public StelGuiBase
 	void init(QGraphicsWidget* topLevelGraphicsWidget) override;
 	void update();
 
+	void showToolTip(const QPoint& scenePos, const QString& text) override;
+
 	StelStyle getStelStyle() const {return currentStelStyle;}
 
 	///////////////////////////////////////////////////////////////////////////
@@ -379,6 +382,8 @@ private slots:
 	AstroCalcDialog* astroCalcDialog;
 	ObsListDialog* obsListDialog;
 
+	StelToolTip* toolTip;
+
 	bool flagShowFlipButtons;
 	StelButton* flipVert;
 	StelButton* flipHoriz;

src/gui/StelGuiItems.cpp

@@ -42,6 +42,7 @@
 #include <QGraphicsLineItem>
 #include <QRectF>
 #include <QDebug>
+#include <QLabel>
 #include <QScreen>
 #include <QGraphicsSceneMouseEvent>
 #include <QGraphicsTextItem>
@@ -55,6 +56,52 @@
 #include <QSettings>
 #include <QGuiApplication>
 
+StelToolTip::StelToolTip(QGraphicsItem* parent)
+	: QGraphicsProxyWidget(parent)
+	, label(new QLabel(""))
+{
+	setZValue(1e38); // Show on top
+	label->setObjectName("StelToolTip");
+	setWidget(label);
+	setVisible(false);
+
+	setSizePolicy({QSizePolicy::Minimum, QSizePolicy::Fixed});
+	connect(dynamic_cast<StelGui*>(StelApp::getInstance().getGui()),
+	        &StelGui::guiStyleChanged, this,
+	        [this](const QString &style){ label->setStyleSheet(style); });
+
+	connect(&StelApp::getInstance(), &StelApp::guiFontSizeChanged,
+	        this, &StelToolTip::setFontSizeFromApp);
+	setFontSizeFromApp(StelApp::getInstance().getGuiFontSize());
+}
+
+void StelToolTip::setFontSizeFromApp(const int size)
+{
+	auto font = QGuiApplication::font();
+	font.setPixelSize(size);
+	setFont(font);
+}
+
+void StelToolTip::showToolTip(const QPoint& scenePos, const QString& text)
+{
+	if (isVisible() && label->text() == text)
+	{
+		// Avoid moving the tooltip when the text doesn't change
+		return;
+	}
+
+	label->setText(text);
+	// The shift avoids clicking the tooltip instead of the control it's annotating
+	const QPoint shift(2, 2);
+	setPos(scenePos + shift);
+	updateGeometry();
+	setVisible(!text.isEmpty());
+}
+
+void StelToolTip::mousePressEvent(QGraphicsSceneMouseEvent*)
+{
+	showToolTip({}, "");
+}
 
 void StelButton::brightenImage(QImage &img, float factor)
 {

src/gui/StelGuiItems.hpp

@@ -20,6 +20,7 @@
 #ifndef STELGUIITEMS_HPP
 #define STELGUIITEMS_HPP
 
+#include <QGraphicsProxyWidget>
 #include <QGraphicsPixmapItem>
 #include <QGraphicsWidget>
 #include <QDebug>
@@ -29,9 +30,23 @@ class QGraphicsSceneMouseEvent;
 class QTimeLine;
 class QGraphicsTextItem;
 class QTimer;
+class QLabel;
 class StelProgressController;
 class QProgressBar;
 
+class StelToolTip : public QGraphicsProxyWidget
+{
+public:
+	StelToolTip(QGraphicsItem* parent);
+	void showToolTip(const QPoint& scenePos, const QString& text);
+protected:
+	void mousePressEvent(QGraphicsSceneMouseEvent* event) override;
+private:
+	void setFontSizeFromApp(int size);
+
+	QLabel* label = nullptr;
+};
+
 // Progress bars in the lower right corner
 class StelProgressBarMgr : public QGraphicsWidget
 {