[PATCH 1/2] qcam: viewfinder_qt: Draw the letterbox background black

[Kieran Bingham]

Quoting Laurent Pinchart (2024-09-05 17:25:07)
> When the widget's aspect ratio doesn't match the camera aspect ratio,
> the viewfinder is rendered letter-boxed. The side rectangles are not
> painted by the viewfinder, and Qt thus renders the parent widget
> background to fill that space.
> 
> To make it black, we have two options:
> 
> - The simplest option is to set the widget's autoFillBackground property
>   to true. This causes Qt to paint the whole widget with its background
>   colour before calling paintEvent(). As the camera image typically
>   covers most (if not all) of the viewfinder widget, this is less
>   efficient.
> 
> - The more complicated option is to pain the letterbox rectangles

s/pain/paint/

>   manually. We can additionally set the widget's WA_OpaquePaintEvent
>   attribute to instruct Qt to skip painting the parent widget. This
>   reduces CPU usage by about 1% (and may reduce GPU usage as well).
> 
> Note that the WA_OpaquePaintEvent attribute has to be disabled when we
> render the stopped icon, as the icon has a transparent background.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/apps/qcam/viewfinder_qt.cpp | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/src/apps/qcam/viewfinder_qt.cpp b/src/apps/qcam/viewfinder_qt.cpp
> index 492648cfa2ff..62b6f27fa23e 100644
> --- a/src/apps/qcam/viewfinder_qt.cpp
> +++ b/src/apps/qcam/viewfinder_qt.cpp
> @@ -44,6 +44,10 @@ ViewFinderQt::ViewFinderQt(QWidget *parent)
>         : QWidget(parent), place_(rect()), buffer_(nullptr)
>  {
>         icon_ = QIcon(":camera-off.svg");
> +
> +       QPalette pal = palette();
> +       pal.setColor(QPalette::Window, Qt::black);
> +       setPalette(pal);
>  }
>  
>  ViewFinderQt::~ViewFinderQt()
> @@ -118,6 +122,7 @@ void ViewFinderQt::render(libcamera::FrameBuffer *buffer, Image *image)
>                 }
>         }
>  

I would probably have a comment here ...

> +       setAttribute(Qt::WA_OpaquePaintEvent, true);
>         update();
>  
>         if (buffer)
> @@ -133,6 +138,7 @@ void ViewFinderQt::stop()
>                 buffer_ = nullptr;
>         }
>  

and here ...

to say why we are starting and sotpping the paint attributes.

> +       setAttribute(Qt::WA_OpaquePaintEvent, false);
>         update();
>  }
>  
> @@ -147,8 +153,22 @@ void ViewFinderQt::paintEvent(QPaintEvent *)
>  {
>         QPainter painter(this);
>  
> -       /* If we have an image, draw it. */
> +       painter.setBrush(palette().window());
> +
> +       /* If we have an image, draw it, with black letterbox rectangles. */
>         if (!image_.isNull()) {
> +               if (place_.width() < width()) {
> +                       QRect rect{ 0, 0, (width() - place_.width()) / 2, height() };
> +                       painter.drawRect(rect);
> +                       rect.moveLeft(place_.right());
> +                       painter.drawRect(rect);
> +               } else {
> +                       QRect rect{ 0, 0, width(), (height() - place_.height()) / 2 };
> +                       painter.drawRect(rect);
> +                       rect.moveTop(place_.bottom());
> +                       painter.drawRect(rect);
> +               }

Seems easy enough.


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

And tested on my X13s

However, I can't currently test qcam -r gles it seems which is crashing
but that's on mainline too so not this series.

> +
>                 painter.drawImage(place_, image_, image_.rect());
>                 return;
>         }
> @@ -174,7 +194,6 @@ void ViewFinderQt::paintEvent(QPaintEvent *)
>         else
>                 point.setY((height() - pixmap_.height()) / 2);
>  
> -       painter.setBackgroundMode(Qt::OpaqueMode);
>         painter.drawPixmap(point, pixmap_);
>  }
>  
> -- 
> Regards,
> 
> Laurent Pinchart
>