#include "sphere.h"

RayIntersect Sphere::CalcRayIntersect(Ray ray)
{
	RayIntersect ri;
	ri.E = 0;
	ri.param_t = -1.0;

	vector3d o_c = ray.o - c;
	double A = ray.d * ray.d;
	double B_2 = ray.d * o_c;
	double C = o_c * o_c - r * r;
	double D = B_2 * B_2 - A * C;

	if(D <= 0.0) return ri;	// Does not intersect

	D = sqrt(D);

	double t = -B_2 - D;

	if(t <= 0) // Behind ray
	{
		t = B_2 - D;
		if(t <= 0) return ri; // This one is behind the ray too.
	}

	ri.E = this;
	ri.param_t = t / A;
	return ri;
}

vector3d Sphere::CalcNormal(Ray ray, RayIntersect&ri)
{
	return (ray.o + ray.d * ri.param_t - c).ret_unit();
}

int Sphere::IntersectionTest(Ray ray)
{
	vector3d o_c = ray.o - c;
	double A = ray.d * ray.d;
	double B_2 = ray.d * o_c;
	double C = o_c * o_c - r * r;
	double D = B_2 * B_2 - A * C;

	// no intersection
	if(D <= 0) return 0;

	// intersects behind me
	if(B_2 > 0 || B_2*B_2 < D + 1e-10) return 0;

	return 1;
}