qcam: viewfinder: Display icon when stopping capture

When stopping capture, display an icon instead of the last frame. This
is required to be able to release the last buffer when the viewfinder
operators in zero-copy mode.

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

src/qcam/assets/feathericons/feathericons.qrc

@@ -1,5 +1,6 @@
 <!DOCTYPE RCC><RCC version="1.0">
 <qresource>
+<file>./camera-off.svg</file>
 <file>./play-circle.svg</file>
 <file>./save.svg</file>
 <file>./stop-circle.svg</file>

src/qcam/viewfinder.cpp

@@ -20,6 +20,7 @@
 ViewFinder::ViewFinder(QWidget *parent)
 	: QWidget(parent), buffer_(nullptr)
 {
+	icon_ = QIcon(":camera-off.svg");
 }
 
 ViewFinder::~ViewFinder()
@@ -114,7 +115,36 @@ QImage ViewFinder::getCurrentImage()
 void ViewFinder::paintEvent(QPaintEvent *)
 {
 	QPainter painter(this);
+
+	/* If we have an image, draw it. */
+	if (!image_.isNull()) {
 		painter.drawImage(rect(), image_, image_.rect());
+		return;
+	}
+
+	/*
+	 * Otherwise, draw the camera stopped icon. Render it to the pixmap if
+	 * the size has changed.
+	 */
+	constexpr int margin = 20;
+
+	if (vfSize_ != size() || pixmap_.isNull()) {
+		QSize vfSize = size() - QSize{ 2 * margin, 2 * margin };
+		QSize pixmapSize{ 1, 1 };
+		pixmapSize.scale(vfSize, Qt::KeepAspectRatio);
+		pixmap_ = icon_.pixmap(pixmapSize);
+
+		vfSize_ = size();
+	}
+
+	QPoint point{ margin, margin };
+	if (pixmap_.width() < width() - 2 * margin)
+		point.setX((width() - pixmap_.width()) / 2);
+	else
+		point.setY((height() - pixmap_.height()) / 2);
+
+	painter.setBackgroundMode(Qt::OpaqueMode);
+	painter.drawPixmap(point, pixmap_);
 }
 
 QSize ViewFinder::sizeHint() const

src/qcam/viewfinder.h

@@ -9,6 +9,7 @@
 
 #include <stddef.h>
 
+#include <QIcon>
 #include <QImage>
 #include <QMutex>
 #include <QSize>
@@ -53,6 +54,12 @@ private:
 	libcamera::PixelFormat format_;
 	QSize size_;
 
+	/* Camera stopped icon */
+	QSize vfSize_;
+	QIcon icon_;
+	QPixmap pixmap_;
+
+	/* Buffer and render image */
 	libcamera::FrameBuffer *buffer_;
 	QImage image_;
 	QMutex mutex_; /* Prevent concurrent access to image_ */