tetrees/Plugins/Wwise/Source/AkAudio/Classes/GTE/Mathematics/ContPointInPolygon2.h

// David Eberly, Geometric Tools, Redmond WA 98052
// Copyright (c) 1998-2020
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
// https://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
// Version: 4.0.2019.08.13

#pragma once

#include <Mathematics/Vector2.h>

// Given a polygon as an order list of vertices (x[i],y[i]) for 0 <= i < N
// and a test point (xt,yt), return 'true' if (xt,yt) is in the polygon and
// 'false' if it is not.  All queries require that the number of vertices
// satisfies N >= 3.

namespace WwiseGTE
{
    template <typename Real>
    class PointInPolygon2
    {
    public:
        // The class object stores a copy of 'points', so be careful about
        // the persistence of 'points' when you have created a
        // PointInPolygon2 object.
        PointInPolygon2(int numPoints, Vector2<Real> const* points)
            :
            mNumPoints(numPoints),
            mPoints(points)
        {
        }

        // Simple polygons (ray-intersection counting).
        bool Contains(Vector2<Real> const& p) const
        {
            bool inside = false;
            for (int i = 0, j = mNumPoints - 1; i < mNumPoints; j = i++)
            {
                Vector2<Real> const& U0 = mPoints[i];
                Vector2<Real> const& U1 = mPoints[j];
                Real rhs, lhs;

                if (p[1] < U1[1])  // U1 above ray
                {
                    if (U0[1] <= p[1])  // U0 on or below ray
                    {
                        lhs = (p[1] - U0[1]) * (U1[0] - U0[0]);
                        rhs = (p[0] - U0[0]) * (U1[1] - U0[1]);
                        if (lhs > rhs)
                        {
                            inside = !inside;
                        }
                    }
                }
                else if (p[1] < U0[1])  // U1 on or below ray, U0 above ray
                {
                    lhs = (p[1] - U0[1]) * (U1[0] - U0[0]);
                    rhs = (p[0] - U0[0]) * (U1[1] - U0[1]);
                    if (lhs < rhs)
                    {
                        inside = !inside;
                    }
                }
            }
            return inside;
        }

        // Algorithms for convex polygons.  The input polygons must have
        // vertices in counterclockwise order.

        // O(N) algorithm (which-side-of-edge tests)
        bool ContainsConvexOrderN(Vector2<Real> const& p) const
        {
            for (int i1 = 0, i0 = mNumPoints - 1; i1 < mNumPoints; i0 = i1++)
            {
                Real nx = mPoints[i1][1] - mPoints[i0][1];
                Real ny = mPoints[i0][0] - mPoints[i1][0];
                Real dx = p[0] - mPoints[i0][0];
                Real dy = p[1] - mPoints[i0][1];
                if (nx * dx + ny * dy > (Real)0)
                {
                    return false;
                }
            }
            return true;
        }

        // O(log N) algorithm (bisection and recursion, like BSP tree)
        bool ContainsConvexOrderLogN(Vector2<Real> const& p) const
        {
            return SubContainsPoint(p, 0, 0);
        }

        // The polygon must have exactly four vertices.  This method is like
        // the O(log N) and uses three which-side-of-segment test instead of
        // four which-side-of-edge tests.  If the polygon does not have four
        // vertices, the function returns false.
        bool ContainsQuadrilateral(Vector2<Real> const& p) const
        {
            if (mNumPoints != 4)
            {
                return false;
            }

            Real nx = mPoints[2][1] - mPoints[0][1];
            Real ny = mPoints[0][0] - mPoints[2][0];
            Real dx = p[0] - mPoints[0][0];
            Real dy = p[1] - mPoints[0][1];

            if (nx * dx + ny * dy > (Real)0)
            {
                // P potentially in <V0,V1,V2>
                nx = mPoints[1][1] - mPoints[0][1];
                ny = mPoints[0][0] - mPoints[1][0];
                if (nx * dx + ny * dy > (Real)0.0)
                {
                    return false;
                }

                nx = mPoints[2][1] - mPoints[1][1];
                ny = mPoints[1][0] - mPoints[2][0];
                dx = p[0] - mPoints[1][0];
                dy = p[1] - mPoints[1][1];
                if (nx * dx + ny * dy > (Real)0)
                {
                    return false;
                }
            }
            else
            {
                // P potentially in <V0,V2,V3>
                nx = mPoints[0][1] - mPoints[3][1];
                ny = mPoints[3][0] - mPoints[0][0];
                if (nx * dx + ny * dy > (Real)0)
                {
                    return false;
                }

                nx = mPoints[3][1] - mPoints[2][1];
                ny = mPoints[2][0] - mPoints[3][0];
                dx = p[0] - mPoints[3][0];
                dy = p[1] - mPoints[3][1];
                if (nx * dx + ny * dy > (Real)0)
                {
                    return false;
                }
            }
            return true;
        }

    private:
        // For recursion in ContainsConvexOrderLogN.
        bool SubContainsPoint(Vector2<Real> const& p, int i0, int i1) const
        {
            Real nx, ny, dx, dy;

            int diff = i1 - i0;
            if (diff == 1 || (diff < 0 && diff + mNumPoints == 1))
            {
                nx = mPoints[i1][1] - mPoints[i0][1];
                ny = mPoints[i0][0] - mPoints[i1][0];
                dx = p[0] - mPoints[i0][0];
                dy = p[1] - mPoints[i0][1];
                return nx * dx + ny * dy <= (Real)0;
            }

            // Bisect the index range.
            int mid;
            if (i0 < i1)
            {
                mid = (i0 + i1) >> 1;
            }
            else
            {
                mid = (i0 + i1 + mNumPoints) >> 1;
                if (mid >= mNumPoints)
                {
                    mid -= mNumPoints;
                }
            }

            // Determine which side of the splitting line contains the point.
            nx = mPoints[mid][1] - mPoints[i0][1];
            ny = mPoints[i0][0] - mPoints[mid][0];
            dx = p[0] - mPoints[i0][0];
            dy = p[1] - mPoints[i0][1];
            if (nx * dx + ny * dy > (Real)0)
            {
                // P potentially in <V(i0),V(i0+1),...,V(mid-1),V(mid)>
                return SubContainsPoint(p, i0, mid);
            }
            else
            {
                // P potentially in <V(mid),V(mid+1),...,V(i1-1),V(i1)>
                return SubContainsPoint(p, mid, i1);
            }
        }

        int mNumPoints;
        Vector2<Real> const* mPoints;
    };
}