Implement Lambertian diffuse scattering

src/camera.c

@@ -29,10 +29,10 @@ static const vec3_t black = { 0.0, 0.0, 0.0 };
 
 static ray_t scatter(hit_t hit, rng_t *rng)
 {
-	const vec3_t rand = rng_vec3(rng);
-	const vec3_t dir
-	    = vec3_dot(rand, hit.normal) > 0.0 ? rand : vec3_scale(rand, -1.0);
-	return (ray_t) { .orig = hit.point, .dir = dir };
+	return (ray_t) {
+		.orig = hit.point,
+		.dir = vec3_add(hit.normal, rng_vec3(rng)),
+	};
 }
 
 static vec3_t