qcam: main_window: Introduce initial hotplug support

Hook up various QCam UI bits with hotplug support introduced
in previous commits. This looks good-enough as first steps
to see how the hotplugging functionality is turning out to be
from application point-of-view.

One can still think of few edge case nuances not yet covered
under this implementation especially around having only one
camera in the system and hotplugging/hot-unplugging it.
Hence, those are intentionally kept out of scope for now. It
might require some thinking on how to handle it on application
level having additional time on hand.

Signed-off-by: Umang Jain <email@uajain.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/qcam/main_window.cpp

@@ -59,6 +59,36 @@ public:
 	}
 };
 
+/**
+ * \brief Custom QEvent to signal hotplug or unplug
+ */
+class HotplugEvent : public QEvent
+{
+public:
+	enum PlugEvent {
+		HotPlug,
+		HotUnplug
+	};
+
+	HotplugEvent(std::shared_ptr<Camera> camera, PlugEvent event)
+		: QEvent(type()), camera_(std::move(camera)), plugEvent_(event)
+	{
+	}
+
+	static Type type()
+	{
+		static int type = QEvent::registerEventType();
+		return static_cast<Type>(type);
+	}
+
+	PlugEvent hotplugEvent() const { return plugEvent_; }
+	Camera *camera() const { return camera_.get(); }
+
+private:
+	std::shared_ptr<Camera> camera_;
+	PlugEvent plugEvent_;
+};
+
 MainWindow::MainWindow(CameraManager *cm, const OptionsParser::Options &options)
 	: saveRaw_(nullptr), options_(options), cm_(cm), allocator_(nullptr),
 	  isCapturing_(false), captureRaw_(false)
@@ -81,6 +111,10 @@ MainWindow::MainWindow(CameraManager *cm, const OptionsParser::Options &options)
 	setCentralWidget(viewfinder_);
 	adjustSize();
 
+	/* Hotplug/unplug support */
+	cm_->cameraAdded.connect(this, &MainWindow::addCamera);
+	cm_->cameraRemoved.connect(this, &MainWindow::removeCamera);
+
 	/* Open the camera and start capture. */
 	ret = openCamera();
 	if (ret < 0) {
@@ -105,6 +139,9 @@ bool MainWindow::event(QEvent *e)
 	if (e->type() == CaptureEvent::type()) {
 		processCapture();
 		return true;
+	} else if (e->type() == HotplugEvent::type()) {
+		processHotplug(static_cast<HotplugEvent *>(e));
+		return true;
 	}
 
 	return QMainWindow::event(e);
@@ -535,6 +572,45 @@ void MainWindow::stopCapture()
 	setWindowTitle(title_);
 }
 
+/* -----------------------------------------------------------------------------
+ * Camera hotplugging support
+ */
+
+void MainWindow::processHotplug(HotplugEvent *e)
+{
+	Camera *camera = e->camera();
+	HotplugEvent::PlugEvent event = e->hotplugEvent();
+
+	if (event == HotplugEvent::HotPlug) {
+		cameraCombo_->addItem(QString::fromStdString(camera->name()));
+	} else if (event == HotplugEvent::HotUnplug) {
+		/* Check if the currently-streaming camera is removed. */
+		if (camera == camera_.get()) {
+			toggleCapture(false);
+			cameraCombo_->setCurrentIndex(0);
+		}
+
+		int camIndex = cameraCombo_->findText(QString::fromStdString(camera->name()));
+		cameraCombo_->removeItem(camIndex);
+	}
+}
+
+void MainWindow::addCamera(std::shared_ptr<Camera> camera)
+{
+	qInfo() << "Adding new camera:" << camera->name().c_str();
+	QCoreApplication::postEvent(this,
+				    new HotplugEvent(std::move(camera),
+						     HotplugEvent::HotPlug));
+}
+
+void MainWindow::removeCamera(std::shared_ptr<Camera> camera)
+{
+	qInfo() << "Removing camera:" << camera->name().c_str();
+	QCoreApplication::postEvent(this,
+				    new HotplugEvent(std::move(camera),
+						     HotplugEvent::HotUnplug));
+}
+
 /* -----------------------------------------------------------------------------
  * Image Save
  */

src/qcam/main_window.h

@@ -32,6 +32,8 @@ using namespace libcamera;
 class QAction;
 class QComboBox;
 
+class HotplugEvent;
+
 enum {
 	OptCamera = 'c',
 	OptHelp = 'h',
@@ -87,8 +89,12 @@ private:
 	int startCapture();
 	void stopCapture();
 
+	void addCamera(std::shared_ptr<Camera> camera);
+	void removeCamera(std::shared_ptr<Camera> camera);
+
 	void requestComplete(Request *request);
 	void processCapture();
+	void processHotplug(HotplugEvent *e);
 	void processViewfinder(FrameBuffer *buffer);
 
 	/* UI elements */