objects.cpp

// Homepage: https://github.com/ananthvk/cpp-raytracer
#include "objects.hpp"

Sphere::Sphere() : center(vec3(0, 0, 0)), radius(0), material_id(0) {}

Sphere::Sphere(vec3 center, double radius, int material_id)
    : center(center), radius(radius), material_id(material_id)
{
}

Intersection Sphere::intersect(const RayParams &params) const
{
    Intersection details;
    // No intersections are expected, so by default occured is set to false
    details.occured = false;
    auto ray = params.ray;
    // Solving sphere-ray quadratic equation
    vec3 AC = ray.origin() - center;
    double a = linalg::dot(ray.direction(), ray.direction());
    double b = 2.0 * linalg::dot(ray.direction(), AC);
    double c = linalg::dot(AC, AC) - radius * radius;
    double discriminant = b * b - 4 * a * c;
    if (discriminant < 0)
    {
        // There is no solution, the ray does not intersect the sphere
        return details;
    }
    double sqd = std::sqrt(discriminant);
    double root = (-b - sqd) / (2.0 * a);
    // Check if the root does not lie within the given range
    if (root < params.t_min || root > params.t_max)
    {
        root = (-b + sqd) / (2.0 * a);
        // Check if the other root does not lie in the range
        if (root < params.t_min || root > params.t_max)
        {
            // Both roots do not lie in range, there is no solution
            return details;
        }
    }
    details.occured = true;
    details.parametric = root;
    details.point = ray.at(root);
    // Find the outward normal or the normal which always points out of the sphere
    details.o_normal = (details.point - center) / radius;
    details.material_id = material_id;
    details.ray = params.ray;
    // Find the local normal, or the normal on the side of the ray
    if (linalg::dot(details.o_normal, ray.direction()) > 0.0)
    {
        // The ray is inside the sphere
        details.front = false;
        details.local_normal = -details.o_normal;
    }
    else
    {
        // The ray is outside the sphere
        details.front = true;
        details.local_normal = details.o_normal;
    }
    return details;
}

void Sphere::set_material_id(int id) { material_id = id; }