Relative to the top left of the parent container
Relative to the top left of the screen
Manages the widgets on the display
UpdateArgs provides access to the widget and UI state during
a call to Widget::update_state
The WidgetId
uniquely describes an instance of a widget.
Creating a new WidgetId
generates a new unique identifier which can
be safely copied and moved around; each copy refers to the same widget.
The intent is that you set up the identifiers once and re-use them,
rather than generating new ids on each iteration of the UI loop so that
the widget state is maintained correctly by the Ui.