From c0d7f106ee8f8a6378f0f0470cfc3ace597c5210 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cobrien@witekio.com>
Date: Sun, 21 Sep 2025 19:00:34 +0100
Subject: [PATCH] Add reflective material

---
 demo.c             |  3 +++
 include/material.h | 14 ++++++++++++++
 src/material.c     | 14 ++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/demo.c b/demo.c
index fbb9dff..271d2ed 100644
--- a/demo.c
+++ b/demo.c
@@ -18,6 +18,9 @@ static const obj_t scene[] = {
 	SPHERE(1.0, 0.0, -3.0, 1.0, LAMBERTIAN(0.6, 0.2, 0.8)),
 	SPHERE(-0.8, 0.0, -3.8, 1.0, LAMBERTIAN(1.0, 1.0, 1.0)),
 	SPHERE(-1.0, -0.8, -2.6, 0.2, LAMBERTIAN(0.9, 0.6, 0.2)),
+	SPHERE(0.3, -0.7, -1.8, 0.3, LAMBERTIAN(1.0, 0.3, 0.1)),
+	SPHERE(-1.6, -0.8, -2.0, 0.2, REFLECTIVE(0.9, 0.9, 0.9)),
+	SPHERE(-6.0, 5.0, -5.0, 6.0, REFLECTIVE(0.9, 0.9, 0.9)),
 	SPHERE(0.0, -1001.0, 0.0, 1000.0, LAMBERTIAN(0.3, 0.3, 0.3)),
 };
 
diff --git a/include/material.h b/include/material.h
index c14475e..c45e7d9 100644
--- a/include/material.h
+++ b/include/material.h
@@ -10,6 +10,12 @@
 		.params = { .lambertian = { .albedo = { r, g, b } } }, \
 	}
 
+#define REFLECTIVE(r, g, b) \
+	{ \
+		.scatter = scatter_reflective, \
+		.params = { .reflective = { .tint = { r, g, b } } }, \
+	}
+
 typedef struct {
 	vec3_t point, normal;
 	double t;
@@ -20,8 +26,13 @@ typedef struct {
 	vec3_t albedo;
 } lambertian_params_t;
 
+typedef struct {
+	vec3_t tint;
+} reflective_params_t;
+
 typedef union {
 	lambertian_params_t lambertian;
+	reflective_params_t reflective;
 } material_params_t;
 
 typedef bool scatter_fn_t(
@@ -36,5 +47,8 @@ typedef struct {
 bool scatter_lambertian(
     material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
     vec3_t *atten_out);
+bool scatter_reflective(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out);
 
 #endif
diff --git a/src/material.c b/src/material.c
index d66a441..978df01 100644
--- a/src/material.c
+++ b/src/material.c
@@ -10,3 +10,17 @@ bool scatter_lambertian(
 	*atten_out = params.lambertian.albedo;
 	return true;
 }
+
+bool scatter_reflective(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out)
+{
+	(void)rng;
+
+	const vec3_t dn
+	    = vec3_scale(hit.normal, -2 * vec3_dot(hit.normal, ray->dir));
+	ray->orig = hit.point;
+	ray->dir = vec3_unit(vec3_add(ray->dir, dn));
+	*atten_out = params.reflective.tint;
+	return true;
+}