This function is only for use in widget implementations. Obtains widget->requisition, unless someone has forced a particular geometry on the widget (e.g. with Widget.setSizeRequest), in which case it returns that geometry instead of the widget's requisition.
This function differs from Widget.sizeRequest in that it retrieves the last size request value from widget->requisition, while Widget.sizeRequest actually calls the "size_request" method on widget to compute the size request and fill in widget->requisition, and only then returns widget->requisition.
Because this function does not call the “size_request” method, it can only be used when you know that widget->requisition is up-to-date, that is, Widget.sizeRequest has been called since the last time a resize was queued. In general, only container implementations have this information; applications should use Widget.sizeRequest.