[libcamera-devel] [PATCH] qcam: viewfinder: Maintain aspect ratio

[Laurent Pinchart]

Hi Kieran,

Thank you for the patch.

On Fri, Mar 26, 2021 at 10:05:40PM +0000, Kieran Bingham wrote:
> Keep the image aspect ratio when displaying in the viewfinder.
> 
> When the window is adjusted to a size that differs in aspect ratio to
> the image, keep the image centered in the main viewpoint while
> maintaining the image's aspect ratio.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
> It's been really annoying me that the QCam viewfinder can scale to fit
> the window, but that it breaks the aspect ratio of the image it
> contains.
> 
> I can't imagine why we would want to viewfind with an incorrect aspect
> ratio, but if we do we can add that as an option later. For now -
> enforce aspect ratio on the QT viewfinder.
> 
> Of course I'm aware that this doesn't cover the GL viewfinder. That can
> either be handled on top, or independently if this is deemed a worthy
> feature.
> 
> 
>  src/qcam/viewfinder_qt.cpp | 19 +++++++++++++++++--
>  src/qcam/viewfinder_qt.h   |  2 ++
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qcam/viewfinder_qt.cpp b/src/qcam/viewfinder_qt.cpp
> index e436714c6bdb..f6ca6793b4e4 100644
> --- a/src/qcam/viewfinder_qt.cpp
> +++ b/src/qcam/viewfinder_qt.cpp
> @@ -15,6 +15,7 @@
>  #include <QMap>
>  #include <QMutexLocker>
>  #include <QPainter>
> +#include <QResizeEvent>
>  #include <QtDebug>
>  
>  #include <libcamera/formats.h>
> @@ -34,7 +35,7 @@ static const QMap<libcamera::PixelFormat, QImage::Format> nativeFormats
>  };
>  
>  ViewFinderQt::ViewFinderQt(QWidget *parent)
> -	: QWidget(parent), buffer_(nullptr)
> +	: QWidget(parent), place_(rect()), buffer_(nullptr)
>  {
>  	icon_ = QIcon(":camera-off.svg");
>  }
> @@ -146,7 +147,7 @@ void ViewFinderQt::paintEvent(QPaintEvent *)
>  
>  	/* If we have an image, draw it. */
>  	if (!image_.isNull()) {
> -		painter.drawImage(rect(), image_, image_.rect());
> +		painter.drawImage(place_, image_, image_.rect());
>  		return;

I'm tempted by a black background ;-)

>  	}
>  
> @@ -179,3 +180,17 @@ QSize ViewFinderQt::sizeHint() const
>  {
>  	return size_.isValid() ? size_ : QSize(640, 480);
>  }
> +
> +void ViewFinderQt::resizeEvent(QResizeEvent *event)
> +{
> +	if (!size_.isValid()) {
> +		event->accept();

I don't think there's a need to accept the event.

> +		return;
> +	}
> +
> +	QPoint zero(0, 0);
> +	place_ = QRect(zero, size_.scaled(event->size(), Qt::KeepAspectRatio));
> +	place_.moveCenter(QRect(zero, size()).center());

This can be simplified:

	place_.setSize(size_.scaled(event->size(), Qt::KeepAspectRatio));
	place_.moveCenter(rect().center());

> +
> +	event->accept();
> +}
> diff --git a/src/qcam/viewfinder_qt.h b/src/qcam/viewfinder_qt.h
> index d755428887c0..bf31b81b3437 100644
> --- a/src/qcam/viewfinder_qt.h
> +++ b/src/qcam/viewfinder_qt.h
> @@ -42,6 +42,7 @@ Q_SIGNALS:
>  
>  protected:
>  	void paintEvent(QPaintEvent *) override;
> +	void resizeEvent(QResizeEvent *) override;
>  	QSize sizeHint() const override;
>  
>  private:
> @@ -49,6 +50,7 @@ private:
>  
>  	libcamera::PixelFormat format_;
>  	QSize size_;
> +	QRect place_;
>  
>  	/* Camera stopped icon */
>  	QSize vfSize_;

-- 
Regards,

Laurent Pinchart