tetrees/Plugins/Wwise/Source/AkAudio/Classes/GTE/Mathematics/IntrOrientedBox2OrientedBox2.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/FIQuery.h>
#include <Mathematics/TIQuery.h>
#include <Mathematics/OrientedBox.h>
#include <Mathematics/Vector2.h>
#include <vector>

// The queries consider the box to be a solid.
//
// The test-intersection query uses the method of separating axes.
// https://www.geometrictools.com/Documentation/MethodOfSeparatingAxes.pdf
// The set of potential separating directions includes the 2 edge normals of
// box0 and the 2 edge normals of box1.  The integer 'separating' identifies
// the axis that reported separation; there may be more than one but only one
// is reported.  The value is 0 when box0.axis[0] separates, 1 when
// box0.axis[1] separates, 2 when box1.axis[0] separates or 3 when
// box1.axis[1] separates.

namespace WwiseGTE
{
    template <typename Real>
    class TIQuery<Real, OrientedBox2<Real>, OrientedBox2<Real>>
    {
    public:
        struct Result
        {
            bool intersect;
            int separating;
        };

        Result operator()(OrientedBox2<Real> const& box0, OrientedBox2<Real> const& box1)
        {
            Result result;

            // Convenience variables.
            Vector2<Real> const* A0 = &box0.axis[0];
            Vector2<Real> const* A1 = &box1.axis[0];
            Vector2<Real> const& E0 = box0.extent;
            Vector2<Real> const& E1 = box1.extent;

            // Compute difference of box centers, D = C1-C0.
            Vector2<Real> D = box1.center - box0.center;

            Real absA0dA1[2][2], rSum;

            // Test box0.axis[0].
            absA0dA1[0][0] = std::fabs(Dot(A0[0], A1[0]));
            absA0dA1[0][1] = std::fabs(Dot(A0[0], A1[1]));
            rSum = E0[0] + E1[0] * absA0dA1[0][0] + E1[1] * absA0dA1[0][1];
            if (std::fabs(Dot(A0[0], D)) > rSum)
            {
                result.intersect = false;
                result.separating = 0;
                return result;
            }

            // Test axis box0.axis[1].
            absA0dA1[1][0] = std::fabs(Dot(A0[1], A1[0]));
            absA0dA1[1][1] = std::fabs(Dot(A0[1], A1[1]));
            rSum = E0[1] + E1[0] * absA0dA1[1][0] + E1[1] * absA0dA1[1][1];
            if (std::fabs(Dot(A0[1], D)) > rSum)
            {
                result.intersect = false;
                result.separating = 1;
                return result;
            }

            // Test axis box1.axis[0].
            rSum = E1[0] + E0[0] * absA0dA1[0][0] + E0[1] * absA0dA1[1][0];
            if (std::fabs(Dot(A1[0], D)) > rSum)
            {
                result.intersect = false;
                result.separating = 2;
                return result;
            }

            // Test axis box1.axis[1].
            rSum = E1[1] + E0[0] * absA0dA1[0][1] + E0[1] * absA0dA1[1][1];
            if (std::fabs(Dot(A1[1], D)) > rSum)
            {
                result.intersect = false;
                result.separating = 3;
                return result;
            }

            result.intersect = true;
            return result;
        }
    };

    template <typename Real>
    class FIQuery<Real, OrientedBox2<Real>, OrientedBox2<Real>>
    {
    public:
        struct Result
        {
            bool intersect;

            // If 'intersect' is true, the boxes intersect in a convex
            // 'polygon'.
            std::vector<Vector2<Real>> polygon;
        };

        Result operator()(OrientedBox2<Real> const& box0, OrientedBox2<Real> const& box1)
        {
            Result result;
            result.intersect = true;

            // Initialize the intersection polygon to box0, listing the
            // vertices in counterclockwise order.
            std::array<Vector2<Real>, 4> vertex;
            box0.GetVertices(vertex);
            result.polygon.push_back(vertex[0]);  // C - e0 * U0 - e1 * U1
            result.polygon.push_back(vertex[1]);  // C + e0 * U0 - e1 * U1
            result.polygon.push_back(vertex[3]);  // C + e0 * U0 + e1 * U1
            result.polygon.push_back(vertex[2]);  // C - e0 * U0 + e1 * U1

            // Clip the polygon using the lines defining edges of box1.  The
            // line normal points inside box1.  The line origin is the first
            // vertex of the edge when traversing box1 counterclockwise.
            box1.GetVertices(vertex);
            std::array<Vector2<Real>, 4> normal =
            {
                box1.axis[1], -box1.axis[0], box1.axis[0], -box1.axis[1]
            };

            for (int i = 0; i < 4; ++i)
            {
                if (Outside(vertex[i], normal[i], result.polygon))
                {
                    // The boxes are separated.
                    result.intersect = false;
                    result.polygon.clear();
                    break;
                }
            }

            return result;
        }

    private:
        // The line normals are inner pointing.  The function returns true
        // when the incoming polygon is outside the line, in which case the
        // boxes do not intersect.  If the function returns false, the
        // outgoing polygon is the incoming polygon intersected with the
        // closed halfspacedefined by the line.
        bool Outside(Vector2<Real> const& origin, Vector2<Real> const& normal,
            std::vector<Vector2<Real>>& polygon)
        {
            // Determine whether the polygon vertices are outside the polygon,
            // inside the polygon, or on the polygon boundary.
            int const numVertices = static_cast<int>(polygon.size());
            std::vector<Real> distance(numVertices);
            int positive = 0, negative = 0, positiveIndex = -1;
            for (int i = 0; i < numVertices; ++i)
            {
                distance[i] = Dot(normal, polygon[i] - origin);
                if (distance[i] > (Real)0)
                {
                    ++positive;
                    if (positiveIndex == -1)
                    {
                        positiveIndex = i;
                    }
                }
                else if (distance[i] < (Real)0)
                {
                    ++negative;
                }
            }

            if (positive == 0)
            {
                // The polygon is strictly outside the line.
                return true;
            }

            if (negative == 0)
            {
                // The polygon is contained in the closed halfspace whose
                // boundary is the line.  It is fully visible and no clipping
                // is necessary.
                return false;
            }

            // The line transversely intersects the polygon. Clip the polygon.
            std::vector<Vector2<Real>> clipPolygon;
            Vector2<Real> vertex;
            int curr, prev;
            Real t;

            if (positiveIndex > 0)
            {
                // Compute the first clip vertex on the line.
                curr = positiveIndex;
                prev = curr - 1;
                t = distance[curr] / (distance[curr] - distance[prev]);
                vertex = polygon[curr] + t * (polygon[prev] - polygon[curr]);
                clipPolygon.push_back(vertex);

                // Include the vertices on the positive side of line.
                while (curr < numVertices && distance[curr] >(Real)0)
                {
                    clipPolygon.push_back(polygon[curr++]);
                }

                // Compute the kast clip vertex on the line.
                if (curr < numVertices)
                {
                    prev = curr - 1;
                }
                else
                {
                    curr = 0;
                    prev = numVertices - 1;
                }
                t = distance[curr] / (distance[curr] - distance[prev]);
                vertex = polygon[curr] + t * (polygon[prev] - polygon[curr]);
                clipPolygon.push_back(vertex);
            }
            else  // positiveIndex is 0
            {
                // Include the vertices on the positive side of line.
                curr = 0;
                while (curr < numVertices && distance[curr] >(Real)0)
                {
                    clipPolygon.push_back(polygon[curr++]);
                }

                // Compute the last clip vertex on the line.
                prev = curr - 1;
                t = distance[curr] / (distance[curr] - distance[prev]);
                vertex = polygon[curr] + t * (polygon[prev] - polygon[curr]);
                clipPolygon.push_back(vertex);

                // Skip the vertices on the negative side of the line.
                while (curr < numVertices && distance[curr] <= (Real)0)
                {
                    curr++;
                }

                // Compute the first clip vertex on the line.
                if (curr < numVertices)
                {
                    prev = curr - 1;
                    t = distance[curr] / (distance[curr] - distance[prev]);
                    vertex = polygon[curr] + t * (polygon[prev] - polygon[curr]);
                    clipPolygon.push_back(vertex);

                    // Keep the vertices on the positive side of the line.
                    while (curr < numVertices && distance[curr] >(Real)0)
                    {
                        clipPolygon.push_back(polygon[curr++]);
                    }
                }
                else
                {
                    curr = 0;
                    prev = numVertices - 1;
                    t = distance[curr] / (distance[curr] - distance[prev]);
                    vertex = polygon[curr] + t * (polygon[prev] - polygon[curr]);
                    clipPolygon.push_back(vertex);
                }
            }

            polygon = clipPolygon;
            return false;
        }
    };
}