panel: Propagate "focus-in" event to browser host

The CEF instance is wrapped in another QWindow instance for Windows
and Linux and thus consumes any focus events that are propagated through
the application.

To ensure that a wrapped CEF instance regains focus after its wrapping
window receives focus, the event needs to be explicitly sent to the
browser host instance it wraps.

Author: PatTheMav

panel/browser-panel-internal.hpp

@@ -24,6 +24,9 @@ extern std::vector<PopupWhitelistInfo> forced_popups;
 class QCefWidgetInternal : public QCefWidget {
 	Q_OBJECT
 
+private:
+	virtual bool eventFilter(QObject *object, QEvent *event) override;
+
 public:
 	QCefWidgetInternal(QWidget *parent, const std::string &url, CefRefPtr<CefRequestContext> rqc);
 	~QCefWidgetInternal();

panel/browser-panel.cpp

@@ -178,6 +178,8 @@ QCefWidgetInternal::QCefWidgetInternal(QWidget *parent, const std::string &url_,
 #ifndef __APPLE__
 	window = new QWindow();
 	window->setFlags(Qt::FramelessWindowHint);
+	window->setObjectName("QCefWidgetInternalWindow");
+	window->installEventFilter(this);
 #endif
 }
 
@@ -186,6 +188,34 @@ QCefWidgetInternal::~QCefWidgetInternal()
 	closeBrowser();
 }
 
+bool QCefWidgetInternal::eventFilter(QObject *object, QEvent *event)
+{
+#ifdef __APPLE__
+	UNUSED_PARAMETER(object);
+	UNUSED_PARAMETER(event);
+
+	return true;
+#else
+	// Return early event does not target the window wrapper or no browser instance is present
+	if (object != window_ || !cefBrowser) {
+		return true;
+	}
+
+	// Also return early if the event is not a "FocusIn" event, only necessary to check if the wrapper is targeted
+	if (event->type() != QEvent::FocusIn) {
+		return true;
+	}
+
+	CefRefPtr<CefBrowserHost> host{cefBrowser->GetHost()};
+
+	if (host) {
+		host->SetFocus(hasFocus);
+	}
+
+	return true;
+#endif
+}
+
 void QCefWidgetInternal::closeBrowser()
 {
 	if (!cefBrowser) {

panel/browser-panel.hpp

@@ -36,6 +36,9 @@ class QCefWidget : public QWidget {
 protected:
 	inline QCefWidget(QWidget *parent) : QWidget(parent) {}
 
+private:
+	virtual bool eventFilter(QObject *object, QEvent *event) = 0;
+
 public:
 	virtual void setURL(const std::string &url) = 0;
 	virtual void setStartupScript(const std::string &script) = 0;