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point_in_poly

```#include "sflmath.h"
int
point_in_poly (const FPOINT *point, const FPOINT *pgon, int nbpoints)
```

Synopsis

Checks if the requested FPOINT is within the specified polygon. Returns TRUE or FALSE.

Source Code - (sflmath.c)

```{
int
inside_flag,
xflag0,
crossings;
const double
*stop;
double
*p,
tx,
ty,
y;

crossings = 0;

tx = point-> x;
ty = point-> y;
y  = pgon [nbpoints - 1].y;

p = (double *) pgon + 1;
if ((y >= ty) != (*p >= ty))
{
if ((xflag0 = (pgon [nbpoints - 1].x >= tx)) ==
(*(double *) pgon >= tx))
{
if (xflag0)
crossings++;
}
else
crossings += (pgon [nbpoints - 1].x - (y - ty) *
(*(double *) pgon - pgon [nbpoints - 1].x) /
(*p - y)) >= tx;
}
stop = &pgon [nbpoints].y;
for (y = *p, p += 2; p <= stop; y = *p, p += 2)
{
if (y >= ty)
{
while ((p < stop) && (*p >= ty))
p += 2;
if (p >= stop)
break;
if ((xflag0 = (*(p - 3) >= tx)) == (*(p - 1) >= tx))
{
if (xflag0)
crossings++;
}
else
crossings += (*(p - 3) - (*(p - 2) - ty) *
(*(p - 1) - *(p - 3)) /
(*p - *(p - 2))) >= tx;
}
else
{
while ((p < stop) && (*p < ty))
p += 2;
if (p >= stop)
break;
if ((xflag0 = (*(p - 3) >= tx)) == (*(p - 1) >= tx))
{
if (xflag0)
crossings++;
}
else
crossings += (*(p - 3) - (*(p - 2) - ty) *
(*(p - 1) -  *(p - 3)) /
(*p - *(p - 2))) >= tx;
}
}
inside_flag = crossings & 0x01;
return (inside_flag);
}
```

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