From a85c25262e717be7247d1969c515940b17955d8b Mon Sep 17 00:00:00 2001
From: Lukas Jiriste <ljiriste@student.42prague.com>
Date: Sat, 23 Nov 2024 11:49:27 +0100
Subject: [PATCH] Implement cylinder-ray intersection detection

This commit makes the project compilable.
---
 inc/miniRT.h |  6 ++++
 src/scene.c  | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/inc/miniRT.h b/inc/miniRT.h
index b836d35..f40ed49 100644
--- a/inc/miniRT.h
+++ b/inc/miniRT.h
@@ -14,6 +14,12 @@ typedef struct s_color_sRGB
 	unsigned char	b;
 }					t_color_sRGB;
 
+typedef struct s_pair
+{
+	double	first;
+	double	second;
+}			t_pair;
+
 typedef struct s_sphere
 {
 	t_color	color;
diff --git a/src/scene.c b/src/scene.c
index e7aa5cc..196ef43 100644
--- a/src/scene.c
+++ b/src/scene.c
@@ -86,6 +86,83 @@ double	get_intersection_arg_nonbounded(const t_ray *ray, const t_object *object)
 		return (NAN);
 }
 
+t_vec3	ray_point(const t_ray *ray, double arg)
+{
+	return (vec_add(ray->start, vec_real_mul(ray->direction, arg)));
+}
+
+double	get_intersection_arg_cylinder_base
+			(const t_ray *ray, const t_cylinder *cylinder)
+{
+	double	res;
+	t_plane	base;
+
+	base.point = vec_add(cylinder->center, vec_real_mul(cylinder->rot_axis, cylinder->height / 2));
+	base.normal = cylinder->rot_axis;
+	res = get_intersection_arg_plane(ray, &base);
+	if (vec_norm(vec_diff(base.point, ray_point(ray, res))) <= cylinder->radius
+			&& vec_scalar_mul(ray->direction, vec_diff(cylinder->center, base.point)) > 0)
+		return (res);
+	base.point = vec_diff(cylinder->center, vec_real_mul(cylinder->rot_axis, cylinder->height / 2));
+	res = get_intersection_arg_plane(ray, &base);
+	if (vec_norm(vec_diff(base.point, ray_point(ray, res))) <= cylinder->radius
+			&& vec_scalar_mul(ray->direction, vec_diff(cylinder->center, base.point)) > 0)
+		return (res);
+	return (NAN);
+}
+
+t_pair	solve_quadratic(double a, double b, double c)
+{
+	t_pair	res;
+	double	det;
+
+	det = b * b - 4 * a * c;
+	if (det < 0)
+	{
+		res.first = NAN;
+		res.second = NAN;
+		return (res);
+	}
+	det = sqrt(det);
+	res.first = (-b - det) / (2 * a);
+	res.second = (-b + det) / (2 * a);
+	return (res);
+}
+
+double	get_intersection_arg_cylinder_around
+			(const t_ray *ray, const t_cylinder *cylinder)
+{
+	t_pair	args;
+	t_vec3	v;
+	t_vec3	u;
+	t_vec3	intersect;
+
+	v = vec_vec_mul(cylinder->rot_axis, ray->direction);
+	u = vec_vec_mul(cylinder->rot_axis, vec_diff(ray->start, cylinder->center));
+	args = solve_quadratic(vec_scalar_mul(v, v), 2 * vec_scalar_mul(v, u),
+			vec_scalar_mul(u, u) - cylinder->radius * cylinder->radius);
+	intersect = ray_point(ray, args.first);
+	if (fabs(vec_scalar_mul(cylinder->rot_axis, intersect)) < cylinder->height / 2
+		&& vec_scalar_mul(ray->direction, vec_diff(cylinder->center, intersect)) > 0)
+		return (args.first);
+	intersect = ray_point(ray, args.second);
+	if (fabs(vec_scalar_mul(cylinder->rot_axis, intersect)) < cylinder->height / 2
+		&& vec_scalar_mul(ray->direction, vec_diff(cylinder->center, intersect)) > 0)
+		return (args.second);
+	return (NAN);
+}
+
+double	get_intersection_arg_cylinder
+			(const t_ray *ray, const t_cylinder *cylinder)
+{
+	double	res;
+
+	res = get_intersection_arg_cylinder_base(ray, cylinder);
+	if (res == NAN)
+		res = get_intersection_arg_cylinder_around(ray, cylinder);
+	return (res);
+}
+
 double	get_intersection_arg_sphere(const t_ray *ray, const t_sphere *sphere)
 {
 	t_vec3	start;
-- 
2.30.2