// Globals which should be set before calling these functions:
//
// int polySides = how many corners the polygon has
// float polyX[] = horizontal coordinates of corners
// float polyY[] = vertical coordinates of corners
// float x, y = point to be tested
//
// The following global arrays should be allocated before calling these functions:
//
// float constant[] = storage for precalculated constants (same size as polyX)
// float multiple[] = storage for precalculated multipliers (same size as polyX)
//
// (Globals are used in this example for purposes of speed. Change as
// desired.)
//
// USAGE:
// Call precalc_values() to initialize the constant[] and multiple[] arrays,
// then call pointInPolygon(x, y) to determine if the point is in the polygon.
//
// The function will return YES if the point x,y is inside the polygon, or
// NO if it is not. If the point is exactly on the edge of the polygon,
// then the function may return YES or NO.
//
// Note that division by zero is avoided because the division is protected
// by the "if" clause which surrounds it.
void precalc_values() {
int i, j=polySides1 ;
for(i=0; i<polySides; i++) {
if(polyY[j]==polyY[i]) {
constant[i]=polyX[i];
multiple[i]=0; }
else {
constant[i]=polyX[i](polyY[i]*polyX[j])/(polyY[j]polyY[i])+(polyY[i]*polyX[i])/(polyY[j]polyY[i]);
multiple[i]=(polyX[j]polyX[i])/(polyY[j]polyY[i]); }
j=i; }}
bool pointInPolygon() {
int i, j=polySides1 ;
bool oddNodes=NO ;
for (i=0; i<polySides; i++) {
if ((polyY[i]< y && polyY[j]>=y
 polyY[j]< y && polyY[i]>=y)) {
oddNodes^=(y*multiple[i]+constant[i]<x); }
j=i; }
return oddNodes; }
