Fine. Our filter classes are implemented, and we can now create our custom widget. This widget will take in input, a source, and a thumbnail picture. Then the thumbnail is immediately processed to display a preview of the filter. If the user clicks on the widget, it will process the source picture and trigger a signal with the filtered picture. Keep in mind that this widget will later be dragged and dropped in the Form Editor of Qt Creator. That's why we will provide properties with getters and setters to select a filter from Qt Creator. Please create a new widget called FilterWidget using the Qt Designer Form Class template. The FilterWidget.ui is really simple:

The titleLabel is a QLabel on top of the QWidget. Below, thumbnailLabel will display the filtered picture thumbnail. Let's switch to FilterWidget.h:

class FILTERPLUGINDESIGNERSHARED_EXPORT FilterWidget : public QWidget 
{ 
    Q_OBJECT 
 
    Q_ENUMS(FilterType) 
    Q_PROPERTY(QString title READ...