From ce45c57662237f8dcfe0352fa10be1bb57edb26b Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Tue, 23 Sep 2025 15:36:08 +0100
Subject: [PATCH] Create material abstraction

---
 CMakeLists.txt     |  1 +
 demo.c             |  7 ++++---
 include/material.h | 40 ++++++++++++++++++++++++++++++++++++++++
 include/obj.h      | 11 ++++-------
 include/vec3.h     |  1 +
 src/camera.c       | 29 +++++++++++++----------------
 src/material.c     | 12 ++++++++++++
 src/vec3.c         |  9 +++++++++
 8 files changed, 84 insertions(+), 26 deletions(-)
 create mode 100644 include/material.h
 create mode 100644 src/material.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1488c0..756b34b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,7 @@ endmacro()
 add_library(batomorph
   src/camera.c
   src/ff.c
+  src/material.c
   src/obj.c
   src/rng.c
   src/vec3.c
diff --git a/demo.c b/demo.c
index 5ccf95c..fbb9dff 100644
--- a/demo.c
+++ b/demo.c
@@ -15,9 +15,10 @@
 static const vec3_t camera_pos = { 0.0, 0.0, 0.0 };
 
 static const obj_t scene[] = {
-	SPHERE(1.0, 0.0, -3.0, 1.0),
-	SPHERE(-2.0, -0.5, -5.0, 1.0),
-	SPHERE(0.0, -1001.0, 0.0, 1000.0),
+	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(0.0, -1001.0, 0.0, 1000.0, LAMBERTIAN(0.3, 0.3, 0.3)),
 };
 
 static pix_t pixbuf[W * H];
diff --git a/include/material.h b/include/material.h
new file mode 100644
index 0000000..c14475e
--- /dev/null
+++ b/include/material.h
@@ -0,0 +1,40 @@
+#ifndef MATERIAL_H
+#define MATERIAL_H
+
+#include "ray.h"
+#include "rng.h"
+
+#define LAMBERTIAN(r, g, b) \
+	{ \
+		.scatter = scatter_lambertian, \
+		.params = { .lambertian = { .albedo = { r, g, b } } }, \
+	}
+
+typedef struct {
+	vec3_t point, normal;
+	double t;
+	bool front;
+} hit_t;
+
+typedef struct {
+	vec3_t albedo;
+} lambertian_params_t;
+
+typedef union {
+	lambertian_params_t lambertian;
+} material_params_t;
+
+typedef bool scatter_fn_t(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out);
+
+typedef struct {
+	scatter_fn_t *scatter;
+	material_params_t params;
+} material_t;
+
+bool scatter_lambertian(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out);
+
+#endif
diff --git a/include/obj.h b/include/obj.h
index f766634..71753cb 100644
--- a/include/obj.h
+++ b/include/obj.h
@@ -1,22 +1,18 @@
 #ifndef OBJ_H
 #define OBJ_H
 
+#include "material.h"
 #include "ray.h"
 
-#define SPHERE(x, y, z, r) \
+#define SPHERE(x, y, z, r, m) \
 	{ \
 		.intersect = intersect_sphere, \
+		.material = m, \
 		.params = { \
 			.sphere = { .centre = { x, y, z }, .radius = r }, \
 		}, \
 	}
 
-typedef struct {
-	vec3_t point, normal;
-	double t;
-	bool front;
-} hit_t;
-
 typedef struct {
 	vec3_t centre;
 	double radius;
@@ -32,6 +28,7 @@ typedef bool intersect_fn_t(
 
 typedef struct {
 	intersect_fn_t *intersect;
+	material_t material;
 	obj_params_t params;
 } obj_t;
 
diff --git a/include/vec3.h b/include/vec3.h
index 5ef216b..d86d925 100644
--- a/include/vec3.h
+++ b/include/vec3.h
@@ -10,6 +10,7 @@ vec3_t vec3_add(vec3_t v, vec3_t u);
 vec3_t vec3_sub(vec3_t v, vec3_t u);
 double vec3_dot(vec3_t v, vec3_t u);
 vec3_t vec3_cross(vec3_t v, vec3_t u);
+vec3_t vec3_hadamard(vec3_t v, vec3_t u);
 double vec3_len(vec3_t v);
 vec3_t vec3_unit(vec3_t v);
 
diff --git a/src/camera.c b/src/camera.c
index 1f10b1a..999df26 100644
--- a/src/camera.c
+++ b/src/camera.c
@@ -30,32 +30,29 @@ static const vec3_t lightblue = { 0.4, 0.6, 1.0 };
 static const vec3_t white = { 1.0, 1.0, 1.0 };
 static const vec3_t black = { 0.0, 0.0, 0.0 };
 
-static ray_t scatter(hit_t hit, rng_t *rng)
-{
-	return (ray_t) {
-		.orig = hit.point,
-		.dir = vec3_add(hit.normal, rng_vec3(rng)),
-	};
-}
-
 static vec3_t
 trace(ray_t ray, const obj_t *scene, unsigned scene_count, rng_t *rng)
 {
-	double coeff = 1.0;
+	vec3_t colour = white;
 	for (unsigned i = 0; i < MAX_ITER; ++i) {
 		hit_t hit = { .t = DBL_MAX };
-		for (unsigned j = 0; j < scene_count; ++j)
-			scene[j].intersect(scene[j].params, ray, &hit, MIN_T, hit.t);
+		material_t material = {};
+		for (unsigned j = 0; j < scene_count; ++j) {
+			if (scene[j].intersect(scene[j].params, ray, &hit, MIN_T, hit.t))
+				material = scene[j].material;
+		}
 
 		if (hit.t == DBL_MAX) {
 			const double a = (ray.dir.y + 1.0) / 2.0;
-			return vec3_scale(
-			    vec3_add(vec3_scale(lightblue, a), vec3_scale(white, 1 - a)),
-			    coeff);
+			const vec3_t bg = vec3_add(
+			    vec3_scale(lightblue, a), vec3_scale(white, 1 - a));
+			return vec3_hadamard(colour, bg);
 		}
 
-		ray = scatter(hit, rng);
-		coeff *= 0.3;
+		vec3_t atten;
+		if (!material.scatter(material.params, hit, rng, &ray, &atten))
+			break;
+		colour = vec3_hadamard(colour, atten);
 	}
 
 	return black;
diff --git a/src/material.c b/src/material.c
new file mode 100644
index 0000000..d66a441
--- /dev/null
+++ b/src/material.c
@@ -0,0 +1,12 @@
+#include "material.h"
+
+bool scatter_lambertian(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out)
+{
+	const vec3_t dir = vec3_unit(vec3_add(hit.normal, rng_vec3(rng)));
+	ray->orig = hit.point;
+	ray->dir = vec3_len(dir) == 0 ? hit.normal : dir;
+	*atten_out = params.lambertian.albedo;
+	return true;
+}
diff --git a/src/vec3.c b/src/vec3.c
index 5dd2e80..84abf94 100644
--- a/src/vec3.c
+++ b/src/vec3.c
@@ -40,6 +40,15 @@ vec3_t vec3_cross(vec3_t v, vec3_t u)
 	};
 }
 
+vec3_t vec3_hadamard(vec3_t v, vec3_t u)
+{
+	return (vec3_t) {
+		.x = v.x * u.x,
+		.y = v.y * u.y,
+		.z = v.z * u.z,
+	};
+}
+
 double vec3_len(vec3_t v)
 {
 	return sqrt(v.x * v.x + v.y * v.y + v.z * v.z);