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/viewfinder.cpp

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * viewfinder.cpp - qcam - Viewfinder
+ */
+
+#include <QImage>
+#include <QPixmap>
+
+#include "format_converter.h"
+#include "viewfinder.h"
+
+ViewFinder::ViewFinder(QWidget *parent)
+	: QLabel(parent), format_(0), width_(0), height_(0), image_(nullptr)
+{
+}
+
+void ViewFinder::display(const unsigned char *raw)
+{
+	converter_.convert(raw, image_->bits());
+
+	QPixmap pixmap = QPixmap::fromImage(*image_);
+	setPixmap(pixmap);
+}
+
+int ViewFinder::setFormat(unsigned int format, unsigned int width,
+			  unsigned int height)
+{
+	int ret;
+
+	ret = converter_.configure(format, width, height);
+	if (ret < 0)
+		return ret;
+
+	format_ = format;
+	width_ = width;
+	height_ = height;
+
+	setFixedSize(width, height);
+
+	delete image_;
+	image_ = new QImage(width, height, QImage::Format_RGB32);
+
+	return 0;
+}