calculate

Returns the absolute position and placement that a popup should be placed at.

The absolute position is very important, as it is used to position the popup on screen.

Specifying the placement is optional. Some widgets may use it to decorate themselves, like tooltips using it to add an appropriate arrow (e.g. left placements result in an arrow on the right), but it is not always required.

This method will always be called after init and is expected to use the two elements provided to it as part of this calculation.