The Rectangle Protocol

The following generic functions comprise the rectangle API. Only rectangle-edges* is in the
rectangle protocol, that is, all classes that are subclasses of rectangle must implement methods
for rectangle-edges*, but need not implement methods for the remaining functions.

=> rectangle-edges* rectangle [Generic Function]
Returns the coordinates of the minimum x and y and maximum x and y of the rectangle rectangle
as four values, min-x, min-y, max-x, and max-y.

=> rectangle-min-point rectangle [Generic Function]
=> rectangle-max-point rectangle [Generic Function]
Returns the min point and max point of the rectangle rectangle, respectively. The position of a
rectangle is specified by its min point.

CLIM will supply default methods for rectangle-min-point and rectangle-max-point on the
protocol class rectangle that are implemented by calling rectangle-edges*.

=> rectangle-min-x rectangle [Generic Function]
=> rectangle-min-y rectangle [Generic Function]
=> rectangle-max-x rectangle [Generic Function]
=> rectangle-max-y rectangle [Generic Function]
Returns (respectively) the minimum x and y coordinate and maximum x and y coordinate of
the rectangle rectangle.

CLIM will supply default methods for these four generic functions on the protocol class rectangle
that are implemented by calling rectangle-edges*.

=> rectangle-width rectangle [Generic Function]
=> rectangle-height rectangle [Generic Function]
=> rectangle-size rectangle [Generic Function]
rectangle-width returns the width of the rectangle rectangle, which is the difference between the
maximum x and its minimum x. rectangle-height returns the height, which is the difference
between the maximum y and its minimum y. rectangle-size returns two values, the width
and the height.

CLIM will supply default methods for these four generic functions on the protocol class rectangle
that are implemented by calling rectangle-edges*.