Is a point inside regular hexagon

Question

I'm looking for advice on the best way to proceed. I'm trying to find whether a given point A:(a, b) is inside a regular hexagon, defined with center O:(x, y) and diameter of circumscribing circle.

It seems like overkill to use Ray-casting, or Winding-number to determine this, for such a simple case, and I'm currently looking at the option of finding the angle (from horizontal) of the line OA, and "normalising" (probably not the right word) it into one of the 6 equilateral triangles and seeing if this new point lies within this triangle.

I get the feeling I'm missing something simple, and there's an easy way (or if I'm really lucky, a Java API) to do this simply and efficiently.

Thanks for your help.

Edit: The hexagon is oriented such that one of the sides is flat with the horizontal.

Answer 1

You can use the equations for each of the sides of the hexagon; with them you can find out if a given point is in the same half-plane as the center of the hexagon.

For example, the top-right side has the equation:

-sqrt(3)x - y + sqrt(3)/2 = 0

You plug in this the coordinates of the point and then the coordinates of the center. If the results have the same sign, then the point is in the bottom-left half-plane (so it may be inside the hexagon).

You then repeat by using the equations of the others sides.
Note that this algorithm will work for any convex polygon.