On Apr 4, 2008, at 5:54 PM, Eric Cooper wrote:
FWIW, I decided to write my own hit test using dot products for
concave polygons. I will
need to do something a bit more involved for convex polygons, but I
don't need that
immediately.
Give this a shot. This is from my AS3 boolean library I'm working on.
I originally wrote the library for AS2 but recently decided to
revisit it for a possible project.
- jon
/**
* Point inside polygon using winding number method
* q Point2d A point 2d structure with x,y properties
* p Polygon A polygon as an array of points in
clockwise order
* returns Boolean Point is inside polygon if winding (w) number
is != 0
*/
private function pointInsidePolygon(q:Point2d, p:Polygon):Boolean
{
var n:int = p.length;
var w:int = 0;
for (i=0; i<n; i++) {
var ip:int = (i+1)%n;
if ( ( p[i].y < q.y ) != ( p[ip].y < q.y ) ) {
if ( p[i].x >= q.x ) {
if ( p[ip].x > q.x ) {
w += 2 * ( p[ip].y > p[i].y ) - 1;
}
else {
if ( ( (p[i].x-q.x)*(p[ip].y-q.y) -
(p[ip].x-q.x)*(p[i].y-q.y) > 0 ) ==
( p[ip].y > p[i].y ) )
{
w += 2 * ( p[ip].y > p[i].y ) -
1;
}
}
}
else {
if ( p[ip].x > q.x ) {
if ( ( (p[i].x-q.x)*(p[ip].y-q.y) -
(p[ip].x-q.x)*(p[i].y-q.y) > 0 ) ==
( p[ip].y > p[i].y ) )
{
w += 2 * ( p[ip].y > p[i].y ) -
1;
}
}
}
}
}
return (w!=0) ? true:false;
}
