BoxShape.cpp

/********************************************************************************
* ReactPhysics3D physics library, http://www.reactphysics3d.com                 *
* Copyright (c) 2010-2024 Daniel Chappuis                                       *
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// Libraries
#include <reactphysics3d/collision/shapes/BoxShape.h>
#include <reactphysics3d/collision/Collider.h>
#include <reactphysics3d/configuration.h>
#include <reactphysics3d/engine/PhysicsCommon.h>
#include <reactphysics3d/memory/MemoryManager.h>
#include <reactphysics3d/collision/RaycastInfo.h>
#include <cassert>

using namespace reactphysics3d;

// Constructor
/**
 * @param halfExtents The vector with the three half-extents of the box
 */
BoxShape::BoxShape(const Vector3& halfExtents, MemoryAllocator& allocator, PhysicsCommon& physicsCommon)
         : ConvexPolyhedronShape(CollisionShapeName::BOX, allocator), mHalfExtents(halfExtents), mPhysicsCommon(physicsCommon) {

    assert(halfExtents.x > decimal(0.0));
    assert(halfExtents.y > decimal(0.0));
    assert(halfExtents.z > decimal(0.0));
}

// Return the local inertia tensor of the collision shape
/**
 * @param mass Mass to use to compute the inertia tensor of the collision shape
 */
Vector3 BoxShape::getLocalInertiaTensor(decimal mass) const {
    const decimal factor = (decimal(1.0) / decimal(3.0)) * mass;
    const decimal xSquare = mHalfExtents.x * mHalfExtents.x;
    const decimal ySquare = mHalfExtents.y * mHalfExtents.y;
    const decimal zSquare = mHalfExtents.z * mHalfExtents.z;
    return Vector3(factor * (ySquare + zSquare), factor * (xSquare + zSquare), factor * (xSquare + ySquare));
}

// Raycast method with feedback information
bool BoxShape::raycast(const Ray& ray, RaycastInfo& raycastInfo, Collider* collider, MemoryAllocator& /*allocator*/) const {

    Vector3 rayDirection = ray.point2 - ray.point1;
    decimal tMin = DECIMAL_SMALLEST;
    decimal tMax = DECIMAL_LARGEST;
    Vector3 normalDirection(decimal(0), decimal(0), decimal(0));
    Vector3 currentNormal;

    // For each of the three slabs
    for (int i=0; i<3; i++) {

        // Account for ray radius
        decimal expandedHalfExtent = mHalfExtents[i] + ray.radius;
        
        // If ray is parallel to the slab
        if (std::abs(rayDirection[i]) < MACHINE_EPSILON) {

            // If the ray's origin is not inside the slab, there is no hit
            if (ray.point1[i] > expandedHalfExtent || ray.point1[i] < -expandedHalfExtent) return false;
        }
        else {

            // Compute the intersection of the ray with the near and far plane of the slab
            decimal oneOverD = decimal(1.0) / rayDirection[i];
            decimal t1 = (-expandedHalfExtent - ray.point1[i]) * oneOverD;
            decimal t2 = (expandedHalfExtent - ray.point1[i]) * oneOverD;
            currentNormal[0] = (i == 0) ? -expandedHalfExtent : decimal(0.0);
            currentNormal[1] = (i == 1) ? -expandedHalfExtent : decimal(0.0);
            currentNormal[2] = (i == 2) ? -expandedHalfExtent : decimal(0.0);

            // Swap t1 and t2 if need so that t1 is intersection with near plane and
            // t2 with far plane
            if (t1 > t2) {
                std::swap(t1, t2);
                currentNormal = -currentNormal;
            }

            // Compute the intersection of the of slab intersection interval with previous slabs
            if (t1 > tMin) {
                tMin = t1;
                normalDirection = currentNormal;
            }
            tMax = std::min(tMax, t2);

            // If tMin is larger than the maximum raycasting fraction, we return no hit
            if (tMin > ray.maxFraction) return false;

            // If the slabs intersection is empty, there is no hit
            if (tMin > tMax) return false;
        }
    }

    // If tMin is negative, we return no hit
    if (tMin < decimal(0.0) || tMin > ray.maxFraction) return false;

    // The ray intersects the three slabs, we compute the hit point
    Vector3 localHitPoint = ray.point1 + tMin * rayDirection;

    // Adjust hit point for sweep radius
    if (ray.radius > decimal(0.0))
    {
        // Clamp point to box
        Vector3 contactPointOnBox;
        contactPointOnBox.x = std::clamp(localHitPoint.x, -mHalfExtents.x, mHalfExtents.x);
        contactPointOnBox.y = std::clamp(localHitPoint.y, -mHalfExtents.y, mHalfExtents.y);
        contactPointOnBox.z = std::clamp(localHitPoint.z, -mHalfExtents.z, mHalfExtents.z);

        // Solve hit point for box
        Vector3 oc = ray.point1 - contactPointOnBox;
        decimal a = rayDirection.lengthSquare(); // a = D.D
        decimal b = 2.0 * rayDirection.dot(oc);  // b = 2 * (D . OC)
        decimal c = oc.lengthSquare() - ray.radius * ray.radius; // c = OC.OC - r^2

        // If origin is inside sphere (c < 0)
        if (c < 0.0) {
            if (b >= 0.0) return false; // Already overlapping and moving away
            tMin = 0.0;
        } else {
            decimal discriminant = b * b - 4.0 * a * c;
            if (discriminant < 0.0) return false; // No real solution, so no hit
            decimal t = (-b - std::sqrt(discriminant)) / (2.0 * a);
            if (t < 0.0 || t > ray.maxFraction) return false; // Hit is behind or too far
            tMin = t;
        }
        
        // From sphere to box
        Vector3 sphereHitPoint = ray.point1 + tMin * rayDirection;
        normalDirection = (sphereHitPoint - contactPointOnBox).getUnit();
        localHitPoint = contactPointOnBox;
    }
    
    raycastInfo.body = collider->getBody();
    raycastInfo.collider = collider;
    raycastInfo.hitFraction = tMin;
    raycastInfo.worldPoint = localHitPoint;
    raycastInfo.worldNormal = normalDirection;

    return true;
}

// Return a given face of the polyhedron
const HalfEdgeStructure::Face& BoxShape::getFace(uint32 faceIndex) const {
    assert(faceIndex < mPhysicsCommon.mBoxShapeHalfEdgeStructure.getNbFaces());
    return mPhysicsCommon.mBoxShapeHalfEdgeStructure.getFace(faceIndex);
}

// Return a given vertex of the polyhedron
const HalfEdgeStructure::Vertex& BoxShape::getVertex(uint32 vertexIndex) const {
    assert(vertexIndex < getNbVertices());
    return mPhysicsCommon.mBoxShapeHalfEdgeStructure.getVertex(vertexIndex);
}

// Return a given half-edge of the polyhedron
const HalfEdgeStructure::Edge& BoxShape::getHalfEdge(uint32 edgeIndex) const {
    assert(edgeIndex < getNbHalfEdges());
    return mPhysicsCommon.mBoxShapeHalfEdgeStructure.getHalfEdge(edgeIndex);
}

// Return the local bounds of the shape in x, y and z directions
/// This method is used to compute the AABB of the box
/**
 * @return The AABB of the shape
 */
AABB BoxShape::getLocalBounds() const {
    return AABB(-mHalfExtents, mHalfExtents);
}