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researchv10 Dan Cross

.ds ZZ DEVELOPMENT PACKAGE
.TH POLYGON 3L "630 MTG"
.XE "polyf()"
.XE "ptinpoly()"
.SH NAME
polygon: polyf, ptinpoly \- polygon routines
.SH SYNOPSIS
.ft B
#include <dmd.h>
.sp
int polyf (bp, poly, np, t, f)
.sp
int ptinpoly (pt, poly, np)
.sp
Bitmap \(**bp;
.br
Point poly[ ];
.br
short np;
.br
Texture16 \(**t;
.br
Code f;	
.br
Point pt;
.SH DESCRIPTION
The
.I polyf
function
is used to fill a closed polygon defined by the
.I np
Points in the array of Points
.IR poly .
The Points are absolute with respect to the Bitmap
.I bp.
The polygon is filled with the Texture16
.I t
using Code
.I f.
The
.I polyf
call
returns 0 if the polygon is filled and -1 if a memory allocation
error occurred during processing, in which case the polygon
is not filled.
.PP
The
.I ptinpoly
call
determines whether the Point
.I pt
is contained in the polygon defined by
.I poly
and
.I np.
The
.I ptinpoly
function
returns 1 if the Point is inside the polygon,
0 if the Point is not inside the polygon,
and -1 if a memory allocation error occurs.
.PP
The polygon can consist of an arbitrary number of filled and unfilled
regions.
For example, a doughnut shape could be formed
without filling
the portion of the Bitmap corresponding to the hole of the doughnut.
This permits a preservation of any background information previously
placed in the Bitmap.
Each region, filled or unfilled, is delimited
by a Point whose x-coordinate has a value of
.I \s-1POLY_F\s+1
(defined in \f3dmd.h\f1).
This Point in
.I poly
is ignored and merely serves as a flag indicating
the start of a new region.
There is always an assumed line connecting the first and last Point
of each region.
.SH EXAMPLE
The following code permits interactive drawing of
a polygon with interior regions, fills it, and then
uses \f2ptinpoly\f1 to determine if the mouse is inside the polygon.
Button 1 is used to draw the points, and button 2 sets a point to \f2POLY_F\f1.  After the polygon fills, clicking button 1 with the mouse inside the polygon will ring the terminal bell.  Clicking button 3 will exit
the drawing and exit the program.
.bp
.PP
.RS 3
.nf
\s-1
.ft CM
#include <dmd.h>

Point npoly[1000];

main()
{
	register int i, j;
	register char c;

	request (MOUSE|KBD);

	i = 0;
	for (;;)
	{
		while (i < 1000){
			wait (MOUSE);
			if( button1 () ){
				npoly[i++] = mouse.xy;
				point (&display, mouse.xy,
				    F_STORE);
				sleep (10);
				continue;
			}
			if( button2 () ){
				npoly[i++].x = POLY_F;
				continue;
			}
			if( button3 () ) break;
		}
		polyf (&display, npoly, i, &T_black,
		    F_STORE);

		wait(MOUSE);

		while( !button3() ){
			wait (MOUSE);
			if( button1() && ptinpoly
			    (mouse.xy, npoly, i) )
				ringbell();

		}
		break;
	}
}
\fR
.fi
.RE
\s+1

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