#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>
#include <geometry.h>

#include "scene.h"

Bbox
spherebb(Point3 pos, double r)
{
	Bbox b;

	b.min.x = pos.x - r;
	b.min.y = pos.y - r;
	b.min.z = pos.z - r;
	b.min.w = 1;

	b.max.x = pos.x + r;
	b.max.y = pos.y + r;
	b.max.z = pos.z + r;
	b.max.w = 1;

	return b;
}

Obj *
newsphere(Point3 pos, double r)
{
	Obj *sphere;

	sphere = malloc(sizeof(Obj));
	if(sphere == nil)
		exits("malloc");

	sphere->type = SPHERE;
	sphere->p = pos;
	sphere->n = (Point3){0, 0, 0, 1};
	sphere->r = r;
	sphere->next = nil;
	sphere->chld = nil;
	sphere->Bbox = spherebb(pos, r);

	return sphere;
}

Hit
spherehit(Obj *sphere, Point3 e, Point3 d)
{
	Point3 ec;
	Hit hit;
	double discrim;
	double smallterm;
	double root;
	double dd;
	double numerator;

	ec = sub3(e, sphere->p);
	smallterm = -dot3(d, ec);

	dd = dot3(d, d);
	discrim = pow(dot3(d, ec), 2) - dd * (dot3(ec, ec) - pow(sphere->r, 2));

	if(discrim < 0)
		goto nohit;

	root = sqrt(discrim);

	numerator = smallterm + root;
	if(smallterm - root < numerator && smallterm - root > 0)
		numerator = smallterm - root;

	hit.d = numerator / dd;
	hit.p = add3(e, mul3(d, hit.d));
	hit.n = mul3(sub3(hit.p, sphere->p), 2);
	hit.ie = e;
	hit.id = mul3(d, hit.d);
	hit.o = sphere;
	hit.c = (Colour){0, 1, 0};

	return hit;
nohit:
	hit.d = 0;
	return hit;
}