```ADD(3G)                                                                ADD(3G)

NAME
eqpt, eqrect, ptinrect, rectinrect, rectXrect, rectclip, Dx, Dy, Pt,
Rect, Rpt - arithmetic on points and rectangles

SYNOPSIS
#include <libc.h>
#include <libg.h>

Point       sub(Point p, Point q)

Point       mul(Point p, int a)

Point       divpt(Point p, int a)

Rectangle   rsubp(Rectangle r, Point p)

Rectangle   rmul(Rectangle r, int a)

Rectangle   rdiv(Rectangle r, int a)

Rectangle   rshift(Rectangle r, int a)

Rectangle   inset(Rectangle r, int n)

Rectangle   rcanon(Rectangle r)

int         eqpt(Point p, Point q)

int         eqrect(Rectangle r, Rectangle s)

int         ptinrect(Point p, Rectangle r)

int         rectinrect(Rectangle r, Rectangle s)

int         rectXrect(Rectangle r, Rectangle s)

int         rectclip(Rectangle *rp, Rectangle b)

int         Dx(Rectangle r);

int         Dy(Rectangle r);

Point       Pt(int x, int y)

Rectangle   Rect(int x0, int y0, int x1, int y1)

Rectangle   Rpt(Point p, Point q)

DESCRIPTION
The functions Pt, Rect and Rpt construct geometrical data types from
their components.  These are implemented as functions.  (Under Plan 9
these are implemented as macros.)

Add returns the Point sum of its arguments: Pt(p.x+q.x, p.y+q.y).  Sub
returns the Point difference of its arguments: Pt(p.x-q.x, p.y-q.y).
Mul returns the Point Pt(p.x*a, p.y*a).  Divpt returns the Point
Pt(p.x/a, p.y/a).

returns the Rectangle Rpt(sub(r.min, p), sub(r.max, p)).  Rmul returns
the Rectangle Rpt(mul(r.min,a), mul(r.max,a)); Rdiv returns the
Rectangle Rpt(div(r.min,a), div(r.max,a)).

Rshift returns the rectangle r with all coordinates either left-shifted
or right-shifted by a, depending on whether a is positive or negative,
respectively.

Inset returns the Rectangle Rect(r.min.x+n, r.min.y+n, r.max.x-n,
r.max.y-n).

Rcanon returns a rectangle with the same extent as r, canonicalized so
that min.x <= max.x, and min.y <= max.y.

Eqpt compares its argument Points and returns 0 if unequal, 1 if equal.
Eqrect does the same for its argument Rectangles.

Ptinrect returns 1 if p is a point within r, and 0 otherwise.

Rectinrect returns 1 if all the pixels in r are also in s, and 0
otherwise.

RectXrect returns 1 if r and s share any point, and 0 otherwise.

Rectclip clips in place the Rectangle pointed to by rp so that it is
completely contained within b.  The return value is 1 if any part of
*rp is within b.  Otherwise, the return value is 0 and *rp is
unchanged.

The functions Dx and Dy give the width (delta x) and height (delta y)
of a Rectangle.  They are implemented as macros.