ClosestPoint.h

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//   Copyright 2024 Jaroslav Pevno, JPLSpatial is offered under the terms of the ISC license:
//
//   Permission to use, copy, modify, and/or distribute this software for any purpose with or
//   without fee is hereby granted, provided that the above copyright notice and this permission
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//   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
#pragma once
 
#include "JPLSpatial/Math/Vec3Traits.h"
 
#include <limits>
 
namespace JPL
{
    template<CVec3 Vec3>
    inline bool GetBaryCentricCoordinates(const Vec3& inA, const Vec3& inB, float& outU, float& outV)
    {
        static constexpr float epsSqr = std::numeric_limits<float>::epsilon() * std::numeric_limits<float>::epsilon();
 
        const Vec3 ab = inB - inA;
        const float denominator = LengthSquared(ab);
        if (denominator < (epsSqr))
        {
            // Degenerate line segment, fallback to points
            if (LengthSquared(inA) < LengthSquared(inB))
            {
                // A closest
                outU = 1.0f;
                outV = 0.0f;
            }
            else
            {
                // B closest
                outU = 0.0f;
                outV = 1.0f;
            }
            return false;
        }
        else
        {
            outV = -DotProduct(inA, ab) / denominator;
            outU = 1.0f - outV;
        }
        return true;
    }
 
    template<CVec3 Vec3>
    inline Vec3 GetClosestPointOnLine(const Vec3& inA, const Vec3& inB, uint32_t& outSet)
    {
        float u, v;
        GetBaryCentricCoordinates(inA, inB, u, v);
        if (v <= 0.0f)
        {
            // inA is closest point
            outSet = 0b0001;
            return inA;
        }
        else if (u <= 0.0f)
        {
            // inB is closest point
            outSet = 0b0010;
            return inB;
        }
        else
        {
            // Closest point lies on line inA inB
            outSet = 0b0011;
            return u * inA + v * inB;
        }
    }
} // namespace JPL