Succeed if the point (X, Y) — in the ellipse's graphical<-device
coordinate system — lies inside the ellipse inscribed in the bounding
box
graphical<-area.
Uses the standard ellipse equation
((X - cx) / rx)² + ((Y - cy) / ry)² ≤ 1
where (cx, cy) is the centre and (rx, ry) the semi-axes. Bbox corners
just miss the shape.
This is the same test used by graphical->in_event_area
to accept a click: that method additionally inflates the ellipse by
event_tolerance pixels on each side so hits within
tolerance of the outline still count.
