A Frame2d has an origin point and a pair of X and Y directions (which are
always perpendicular to each other). It can be thought of as:
relativeTo
and placeIn functions that convert values of that type from global
coordinates to local coordinates in a particular frame, and vice versa.Frame2d could be
used to define the position and orientation of a spaceship in a 2D game.
Movement of the ship would then be done by translating and rotating the
frame.