fig, a drawing editor, mostly stolen from Gargoyle.

A picture is constructed of objects (polygons and circles).
Objects are constructed by placing the `current point' at
each of a sequence of points that define the object.

There is a collection of alignment objects toward which the
current point gravitates when dragged.

Each object in the scene is an alignment object.
Additionally, the user can specify a set of points and lines on the
screen (hot spots) and a set of rules by which alignment
objects should be created, e.g.:
	circles of a given radius around each hot point
	lines of a given slope from each hot point
	lines a given distance away from each hot line
	lines of at given angle at the endpoints of each hot line
	midpoint of each hot line

The user can specify that appropriate pieces (points and lines of a polygon,
center of a circle) of the current selection be
made hot if it is being edited, (but not if it's being transformed).

File commands:
	read/write a file
	start over
Selection commands:
	select a circle/point/line/polygon
Object creation commands:
	start a new circle/polygon (selects an empty polygon)
Object editing commands:
	change center/radius of selected circle
	break the selected edge
	move the selected point
	close the selected polygon
	delete the selected object
Transformation commands:
	drop anchor
	translate/rotate/scale the selected object
Measurement commands:
	measure/type an angle/distance/slope
Alignment construction commands:
	circles of a given radius around each hot point
	lines of a given slope from each hot point
	lines a given distance away from each hot line
	lines at a given angle at the endpoints of each hot line
	midpoints of hot lines
Hot spot selection commands:
	heat/cool the selected object
	cool everything
	always/never heat the selection being edited

Global definitions:
struct object{
	char type;			/* CIRCLE/POLYGON/CLOSED/POINT/LINE */
	Point c;			/* center of circle */
	int r;				/* radius of circle */
	int nv;				/* number of vertices in polygon */
	Point *v;			/* polygon/line/point vertices */
	struct object *container;	/* polygon containing the point or line */
	struct object *next;		/* next member of list */
};
/*
 * object types
 */
#define	CIRCLE	1	/* a circle */
#define	POLYGON	2	/* an open polygon: first and last vertices unconnected */
#define	CLOSED	3	/* a closed polygon: last vertex connected to first */
#define	POINT	4	/* a single point, possibly part of some polygon */
#define	LINE	5	/* a single line, possibly part of some polygon */
struct object *scene;	/* the thing being drawn (type in CIRCLE, POLYGON) */
struct object *align;	/* list of gravitating objects (CIRCLE, POINT, LINE) */
struct object *hotspot;	/* list of hot spots (POINT, LINE) */
struct object *select;	/* selected objects (CIRCLE, POLYGON, POINT, LINE) */
Point current;		/* the current point */
char hotsel;		/* make selection hot when editing */
Point anchor;		/* reference point for transformations */
struct alignrule{
	char type;	/* PTCIRC/PTANG/LNDIST/LNANG/MIDPT */
	int v;		/* rule parameter */
	struct alignrule *next;
}*rule;
/*
 * alignment rule types
 */
#define	PTCIRC	1	/* a circle of radius v at each hot point */
#define	PTANG	2	/* a line at angle v at each hot point */
#define	LNDIST	3	/* a line at distance v from each hot line */
#define	LNANG	4	/* a line at angle v from each end of each hot line */
#define	MIDPT	5	/* the midpoint of each hot line */