Re: [pygame] Re: Hexagonal collision detection?

[Chris McCormick <chris@xxxxxxxxxxxx>]

Here is what I use to do [I think] the same thing:

        def PointIn(self, pos):
                """
                This code is patterned after [Franklin, 2000]
                http://www.geometryalgorithms.com/Archive/algorithm_0103/algorithm_0103.htm
                Tells us if the point is in this polygon
                """
                cn = 0  # the crossing number counter
                pts = self.points[:]
                pts.append(self.points[0])
                for i in range(len(pts) - 1):
                        if (((pts[i][1] <= pos[1]) and (pts[i+1][1] > pos[1])) or ((pts[i][1] > pos[1]) and (pts[i+1][1] <= pos[1]))):
                                if (pos[0] < pts[i][0] + float(pos[1] - pts[i][1]) / (pts[i+1][1] - pts[i][1]) * (pts[i+1][0] - pts[i][0])):
                                        cn += 1
                return bool(cn % 2)

This is the method of a class which has a member called 'points' - e.g. a class
which represents a polygon.

Chris.

On Wed, Sep 16, 2009 at 02:55:37PM -0700, Ian Mallett wrote:
> Hi,
> 
> I actually don't remember where the function came from...it would have been
> several years ago now.  I presented it simply, as I though it would be
> useful.  At the time I wrote the original code, I had no idea how it worked,
> and now . . . I still don't :P
> 
> I can tell you it basically tests the point against every line segment on
> the polygon.  Naturally, if it falls on the "inside side" of every line,
> then the point is in the polygon.  Googling "point polygon collision" brings
> up this method.  Still not sure how that the code actually does that though.
> 
> Ian
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