Extracts the position of a DOM MouseEvent and normalises it. Useful for
implementing mouse input.
Parameters
event: MouseEvent
domElem: HTMLElement
Returns [number, number]
Returns a 2-tuple containing the normalised coordinates; the first
element contains the normalised x axis, and the second element contains the
normalised y axis
Extracts the position of a DOM MouseEvent and normalises it. Useful for implementing mouse input.