CLIM 2 User Guide

3.6.3 CLIM point objects
A point is a mathematical point in the drawing plane, which is identified by its coordinates, a pair of real
numbers. Points have neither area nor length. Note that a point is not the same thing as a pixel; CLIM's
model of the drawing plane has continuous coordinates.
You can create point objects and use them as arguments to the drawing functions. Alternatively, you can
use the spread versions of the drawing functions, that is the drawing functions with stars appended to their
names. For example, instead of draw-point, use draw-point* which take two arguments specifying
a point by its coordinates. (Note that we generally recommend the use of the spread versions, since the
CLIM implementation is optimized for those functions.)
The operations for creating and dealing with points are:
point
[Class]
■ The protocol class that corresponds to a mathematical point. If you want to create a new class that
obeys the point protocol, it must be a subclass of point.
standard-point
■ A class that implements a point. This is the class that make-point instantiates.
[Class]
make-point
Arguments: x y
[Function]
■ Creates and returns a point object whose coordinates are x and y. The point object is an instance
of standard-point.
point-position
Arguments: point
■ Returns two values, the x and y coordinates of point.
point-x
Arguments: point
■ Returns the x coordinate of point.
point-y
Arguments: point
■ Returns the y coordinate of point.
[Generic function]
[Generic function]
[Generic function]
3.6.4 Polygons and polylines in CLIM
A polyline is a path that consists of one or more line segments joined consecutively at their end-points. A
line is a polyline that has only a single segment.
Polylines that have the end-point of their last line segment coincident with the start-point of their first line
segment are called closed; this use of the term ‘closed’ should not be confused with closed sets of points.
A polygon is an area bounded by a closed polyline.
If the boundary of a polygon intersects itself, the odd-even winding-rule defines the polygon: a point is
inside the polygon if a ray from the point to infinity crosses the boundary an odd number of times.
46 CLIM 2.2 User Guide