Line box intersection

Cplusc (457)
I am casting a line from any arbitrary point in a 3D space and I want to check if the line intersect with the box or not. I found the code for this here https://3dkingdoms.com/weekly/weekly.php?a=3 and added the necessary parts to check if the code works correctly. here is the code I have 

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#include <iostream>

struct CVec3 {
    float x, y, z;

    CVec3 operator+(const CVec3& other) const {
        return { x + other.x, y + other.y, z + other.z };
    }

    CVec3 operator-(const CVec3& other) const {
        return { x - other.x, y - other.y, z - other.z };
    }

    CVec3 operator*(float scalar) const {
        return { x * scalar, y * scalar, z * scalar };
    }
};

int inline GetIntersection(float fDst1, float fDst2, CVec3 P1, CVec3 P2, CVec3& Hit) {
    if ((fDst1 * fDst2) >= 0.0f) return 0;
    if (fDst1 == fDst2) return 0;
    Hit = P1 + (P2 - P1) * (-fDst1 / (fDst2 - fDst1));
    return 1;
}

int inline InBox(CVec3 Hit, CVec3 B1, CVec3 B2, const int Axis) {
    if (Axis == 1 && Hit.z > B1.z && Hit.z < B2.z && Hit.y > B1.y && Hit.y < B2.y) return 1;
    if (Axis == 2 && Hit.z > B1.z && Hit.z < B2.z && Hit.x > B1.x && Hit.x < B2.x) return 1;
    if (Axis == 3 && Hit.x > B1.x && Hit.x < B2.x && Hit.y > B1.y && Hit.y < B2.y) return 1;
    return 0;
}

int CheckLineBox(CVec3 B1, CVec3 B2, CVec3 L1, CVec3 L2, CVec3& Hit) {
    if (L2.x < B1.x && L1.x < B1.x) return false;
    if (L2.x > B2.x && L1.x > B2.x) return false;
    if (L2.y < B1.y && L1.y < B1.y) return false;
    if (L2.y > B2.y && L1.y > B2.y) return false;
    if (L2.z < B1.z && L1.z < B1.z) return false;
    if (L2.z > B2.z && L1.z > B2.z) return false;
    if (L1.x > B1.x && L1.x < B2.x &&
        L1.y > B1.y && L1.y < B2.y &&
        L1.z > B1.z && L1.z < B2.z) {
        Hit = L1;
        return true;
    }
    if ((GetIntersection(L1.x - B1.x, L2.x - B1.x, L1, L2, Hit) && InBox(Hit, B1, B2, 1))
        || (GetIntersection(L1.y - B1.y, L2.y - B1.y, L1, L2, Hit) && InBox(Hit, B1, B2, 2))
        || (GetIntersection(L1.z - B1.z, L2.z - B1.z, L1, L2, Hit) && InBox(Hit, B1, B2, 3))
        || (GetIntersection(L1.x - B2.x, L2.x - B2.x, L1, L2, Hit) && InBox(Hit, B1, B2, 1))
        || (GetIntersection(L1.y - B2.y, L2.y - B2.y, L1, L2, Hit) && InBox(Hit, B1, B2, 2))
        || (GetIntersection(L1.z - B2.z, L2.z - B2.z, L1, L2, Hit) && InBox(Hit, B1, B2, 3)))
        return true;

    return false;
}

int main() {
    CVec3 B1{ 0.0f, 0.0f, 0.0f };
    CVec3 B2{ 1.0f, 1.0f, 1.0f };
    CVec3 L1{ -1.0f, -1.0f, -1.0f };
    CVec3 L2{ 1.0f, 1.0f, 1.0f };
    CVec3 Hit;

    int result = CheckLineBox(B1, B2, L1, L2, Hit);

    if (result) {
        std::cout << "Line intersects with the box. Intersection point: (" << Hit.x << ", " << Hit.y << ", " << Hit.z << ")\n";
    }
    else {
        std::cout << "Line does not intersect with the box.\n";
    }

    return 0;
}


B1 - the smallest values of X, Y, Z
B2 - the largest values of X, Y, Z


For the given example the line must intersect with the box, but the code detect no intersection. any idea on why I am not getting the correct answer.
Last edited on
TheIdeasMan (6817)
Now is a great time to do some debugging, with a debugger :+)

Actually, does it compile? I wonder, it seems you are missing an operator. In another location, you have the operator, but it is in the wrong order.
Last edited on
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