Page 12 Table of Contents Index Page 14
Chapters
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30
A, B, C, D, E




Chapter 3

Regions

CLIM provides definitions for a variety of geometric objects, including points, lines, elliptical
arcs, regions, and transformations. Both the graphics and windowing modules use the same set
of geometric objects and functions. In this section, we describe regions, points, and the basic
region classes. Transformations will be described in Chapter 5.

Most of these objects are described as if they are implemented using standard classes. However,
this need not be the case. In particular, they may be implemented using structure classes, and
some classes may exist only to name a place in the hierarchy|all members of such a class will
be instances of that class's subclasses. The most important concern is that these classes must
allow specializing generic functions.

The coordinate system in which the geometric objects reside is an abstract, continuous coordinate
system. This abstract coordinate system is converted into "real world" coordinates only during
operations such as rendering one of the objects on a display device.

Angles are measured in radians. Following standard conventions, when an angle is measured
relative to a given line, a positive angle indicates an angle counter-clockwise from the line in the
plane. When the angle from the positive x axis to the positive y axis is positive (that is, the
positive y axis is counter-clockwise from the positive x axis), the coordinate system is said to
be right-handed. When this angle is negative, the coordinate system is said to be left-handed.
Thus, the cartesian coordinate system with x increasing to the right and y increasing upward is
right-handed. A coordinate system with y increasing down is left-handed. (By default, CLIM
streams are left handed, but no such default exists for sheets in general.)

3.1 General Regions

A region is an object that denotes a set of mathematical points in the plane. Regions include
their boundaries, that is, they are closed. Regions have infinite resolution.

Page 12 Table of Contents Index Page 14
Chapters
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30
A, B, C, D, E