Layering UI elements in Qt Designer

Question

I have a QLabel that I'm constantly setting it's pixmap (video playback). In my application the user needs to be able to draw (boxes) above the video. How can I layer one of the QPaintDevice classes (QWidget, QPixmap, QImage, etc.) directly above and with the same size as the QLabel for painting. This element will need to have a transparent background so shapes drawn on it will appear over the video.

Answer 1

Add the widget you want to draw shapes on as a child widget of the video label. Add a layout first so the child widget will match the size of the parent widget. The code would be something like this:

QHBoxLayout *layout = new QHBoxLayout(videoWidget);
QLabel *overlayWidget = new QLabel();
overlayWidget->setAlignment(Qt::AlignCenter);
overlayWidget->setText("Overlaid Text");
layout->addWidget(overlayWidget);

You should see the text overlaid on the video and it should remain centered over the video widget if it is resized. For your final code, you would use some widget subclass of your own that allowed you to intercept mouse actions and draw rectangles but that's the basic idea.