Render a diffuse sphere

color.c

@@ -7,6 +7,10 @@ Color color_add(Color c1, Color c2) {
   return (Color){c1.r + c2.r, c1.g + c2.g, c1.b + c2.b};
 }
 
+Color color_mul(double t, Color c) {
+  return (Color){t * c.r, t * c.g, t * c.b};
+}
+
 Color color_lerp(Color c1, Color c2, double t) {
   return (Color){
       (1.0 - t) * c1.r + t * c2.r,

color.h

@@ -8,6 +8,7 @@ typedef struct Color {
 } Color;
 
 Color color_add(Color c1, Color c2);
+Color color_mul(double t, Color c);
 
 Color color_lerp(Color c1, Color c2, double t);
 

main.c

@@ -11,11 +11,17 @@
 #include "utils.h"
 #include "vec3.h"
 
-Color ray_color(Ray r, Hittable world) {
+Color ray_color(Ray r, Hittable world, int depth) {
+  if (depth <= 0)
+    return (Color){0, 0, 0};
+
   HitRecord record;
   if (hittable_hit(&world, r, 0, DBL_MAX, &record)) {
-    return (Color){0.5 * (record.normal.x + 1), 0.5 * (record.normal.y + 1),
-                   0.5 * (record.normal.z + 1)};
+    Point3 target = point3_add(
+        record.p, vec3_add(record.normal, vec3_random_in_unit_sphere()));
+    return color_mul(0.5,
+                     ray_color((Ray){record.p, point3_sub(target, record.p)},
+                               world, depth - 1));
   }
   Vec3 unit_direction = vec3_normalize(r.direction);
   double t = 0.5 * (unit_direction.y + 1.0);
@@ -30,6 +36,7 @@ int main(void) {
   const int image_width = 256;
   const int image_height = (int)(image_width / aspect_ratio);
   const int samples_per_pixel = 100;
+  const int max_depth = 50;
 
   /* World */
   HittableList object_list = {0};
@@ -57,7 +64,7 @@ int main(void) {
         double u = (i + random_double()) / (image_width - 1);
         double v = (j + random_double()) / (image_height - 1);
         Ray r = camera_get_ray(&camera, u, v);
-        pixel_color = color_add(pixel_color, ray_color(r, world));
+        pixel_color = color_add(pixel_color, ray_color(r, world, max_depth));
       }
       color_write(stdout, pixel_color, samples_per_pixel);
     }

vec3.c

@@ -1,4 +1,5 @@
 #include "vec3.h"
+#include "utils.h"
 
 #include <math.h>
 
@@ -33,3 +34,28 @@ Vec3 vec3_cross(Vec3 v1, Vec3 v2) {
       v1.x * v2.y - v1.y * v2.x,
   };
 }
+
+Vec3 vec3_random(void) {
+  return (Vec3){
+      random_double(),
+      random_double(),
+      random_double(),
+  };
+}
+
+Vec3 vec3_random_in_range(double min, double max) {
+  return (Vec3){
+      random_double_in_range(min, max),
+      random_double_in_range(min, max),
+      random_double_in_range(min, max),
+  };
+}
+
+Vec3 vec3_random_in_unit_sphere(void) {
+  while (1) {
+    Vec3 result = vec3_random_in_range(-1, 1);
+    if (vec3_length2(result) >= 1)
+      continue;
+    return result;
+  }
+}

vec3.h

@@ -19,4 +19,8 @@ Vec3 vec3_normalize(Vec3 v);
 double vec3_dot(Vec3 v1, Vec3 v2);
 Vec3 vec3_cross(Vec3 v1, Vec3 v2);
 
+Vec3 vec3_random(void);
+Vec3 vec3_random_in_range(double min, double max);
+Vec3 vec3_random_in_unit_sphere(void);
+
 #endif /* INCLUDED_VEC3_H */