qcam: Add Qt-based GUI application

qcam is a sample camera GUI application based on Qt. It demonstrates
integration of the Qt event loop with libcamera.

The application lets the user select a camera through the GUI, and then
captures a single stream from the camera and displays it in a window.
Only streams in YUYV formats are supported for now.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/qcam/main.cpp

@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * main.cpp - cam - The libcamera swiss army knife
+ */
+
+#include <iostream>
+#include <signal.h>
+#include <string.h>
+
+#include <QApplication>
+
+#include <libcamera/camera_manager.h>
+
+#include "main_window.h"
+#include "../cam/options.h"
+#include "qt_event_dispatcher.h"
+
+void signalHandler(int signal)
+{
+	std::cout << "Exiting" << std::endl;
+	qApp->quit();
+}
+
+OptionsParser::Options parseOptions(int argc, char *argv[])
+{
+	OptionsParser parser;
+	parser.addOption(OptCamera, OptionString,
+			 "Specify which camera to operate on", "camera",
+			 ArgumentRequired, "camera");
+	parser.addOption(OptHelp, OptionNone, "Display this help message",
+			 "help");
+
+	OptionsParser::Options options = parser.parse(argc, argv);
+	if (options.isSet(OptHelp))
+		parser.usage();
+
+	return options;
+}
+
+int main(int argc, char **argv)
+{
+	QApplication app(argc, argv);
+	int ret;
+
+	OptionsParser::Options options = parseOptions(argc, argv);
+	if (!options.valid())
+		return EXIT_FAILURE;
+	if (options.isSet(OptHelp))
+		return 0;
+
+	struct sigaction sa = {};
+	sa.sa_handler = &signalHandler;
+	sigaction(SIGINT, &sa, nullptr);
+
+	std::unique_ptr<EventDispatcher> dispatcher(new QtEventDispatcher());
+	CameraManager *cm = CameraManager::instance();
+	cm->setEventDispatcher(std::move(dispatcher));
+
+	ret = cm->start();
+	if (ret) {
+		std::cout << "Failed to start camera manager: "
+			  << strerror(-ret) << std::endl;
+		return EXIT_FAILURE;
+	}
+
+	MainWindow *mainWindow = new MainWindow(options);
+	mainWindow->show();
+	ret = app.exec();
+	delete mainWindow;
+
+	cm->stop();
+	return ret;
+}