RaySphere.h

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// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <Jolt/Math/FindRoot.h>
 
JPH_NAMESPACE_BEGIN
 
JPH_INLINE float RaySphere(Vec3Arg inRayOrigin, Vec3Arg inRayDirection, Vec3Arg inSphereCenter, float inSphereRadius)
{
    // Solve: |RayOrigin + fraction * RayDirection - SphereCenter|^2 = SphereRadius^2 for fraction
    Vec3 center_origin = inRayOrigin - inSphereCenter;
    float a = inRayDirection.LengthSq();
    float b = 2.0f * inRayDirection.Dot(center_origin);
    float c = center_origin.LengthSq() - inSphereRadius * inSphereRadius;
    float fraction1, fraction2;
    if (FindRoot(a, b, c, fraction1, fraction2) == 0)
        return c <= 0.0f? 0.0f : FLT_MAX; // Return if origin is inside the sphere
 
    // Sort so that the smallest is first
    if (fraction1 > fraction2)
        std::swap(fraction1, fraction2);
 
    // Test solution with lowest fraction, this will be the ray entering the sphere
    if (fraction1 >= 0.0f)
        return fraction1; // Sphere is before the ray start
 
    // Test solution with highest fraction, this will be the ray leaving the sphere
    if (fraction2 >= 0.0f)
        return 0.0f; // We start inside the sphere
 
    // No solution
    return FLT_MAX;
}
 
JPH_INLINE int RaySphere(Vec3Arg inRayOrigin, Vec3Arg inRayDirection, Vec3Arg inSphereCenter, float inSphereRadius, float &outMinFraction, float &outMaxFraction)
{
    // Solve: |RayOrigin + fraction * RayDirection - SphereCenter|^2 = SphereRadius^2 for fraction
    Vec3 center_origin = inRayOrigin - inSphereCenter;
    float a = inRayDirection.LengthSq();
    float b = 2.0f * inRayDirection.Dot(center_origin);
    float c = center_origin.LengthSq() - inSphereRadius * inSphereRadius;
    float fraction1, fraction2;
    switch (FindRoot(a, b, c, fraction1, fraction2))
    {
    case 0:
        if (c <= 0.0f)
        {
            // Origin inside sphere
            outMinFraction = outMaxFraction = 0.0f;
            return 1;
        }
        else
        {
            // Origin outside of the sphere
            return 0;
        }
        break;
 
    case 1:
        // Ray is touching the sphere
        outMinFraction = outMaxFraction = fraction1;
        return 1;
 
    default:
        // Ray enters and exits the sphere
 
        // Sort so that the smallest is first
        if (fraction1 > fraction2)
            std::swap(fraction1, fraction2);
 
        outMinFraction = fraction1;
        outMaxFraction = fraction2;
        return 2;
    }
}
 
JPH_NAMESPACE_END