diff --git a/.gitignore b/.gitignore
index 8be3252..59cbbf9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,6 +10,7 @@ test/test_rays
 test/test_lights
 test/test_materials
 test/test_spheres
+test/test_world
 raytracer
 *.ppm
 *.png
\ No newline at end of file
diff --git a/intersections.h b/intersections.h
index 37df9a1..a68d98a 100644
--- a/intersections.h
+++ b/intersections.h
@@ -1,11 +1,14 @@
 #pragma once
 
+#include <stdarg.h>
+#include <assert.h>
+
 #include "spheres.h"
 #include "rays.h"
 
 struct intersection {
   float t;
-  struct sphere const * const object;
+  struct sphere const * object;
 };
 
 struct intersection intersection(float t, struct sphere const * const object)
@@ -13,32 +16,26 @@ struct intersection intersection(float t, struct sphere const * const object)
   return (struct intersection){ t, object };
 }
 
+#define MAX_INTERSECTIONS 1024
+
 struct intersections {
   int count;
-  struct intersection i[];
+  struct intersection i[MAX_INTERSECTIONS];
 };
 
-struct intersections2 {
-  int count;
-  struct intersection i[2];
-};
-
-struct intersections4 {
-  int count;
-  struct intersection i[4];
-};
-
-struct intersections2 intersections2(struct intersection a, struct intersection b)
+inline static void intersections(struct intersections * intersections, int count, ...)
 {
-  return (struct intersections2){ 2, {a, b} };
+  va_list ap;
+  va_start(ap, count);
+  for (int i = 0; i < count; i++) {
+    intersections->i[i] = va_arg(ap, struct intersection);
+  }
+  va_end(ap);
+
+  intersections->count = count;
 }
 
-struct intersections4 intersections4(struct intersection a, struct intersection b, struct intersection c, struct intersection d)
-{
-  return (struct intersections4){ 4, {a, b, c, d} };
-}
-
-inline static struct intersections2 intersect(struct sphere const * const s, struct ray r)
+inline static void intersect(struct sphere const * const s, struct ray r, struct intersections * intersections)
 {
   struct mat4x4 m = mat4x4_inverse(&s->transform);
   struct ray r2 = ray_transform(r, &m);
@@ -51,15 +48,16 @@ inline static struct intersections2 intersect(struct sphere const * const s, str
   float discriminant = b * b - 4 * a * c;
 
   if (discriminant < 0) {
-    return (struct intersections2) { 0 };
+    return;
   } else {
     float root = sqrtf(discriminant);
     float t1 = (-b - root) / (2 * a);
     float t2 = (-b + root) / (2 * a);
 
-    return
-      intersections2(intersection(t1, s),
-                     intersection(t2, s));
+    intersections->i[intersections->count++] = intersection(t1, s);
+    intersections->i[intersections->count++] = intersection(t2, s);
+    assert(intersections->count < MAX_INTERSECTIONS);
+    return;
   }
 }
 
@@ -74,3 +72,71 @@ inline static struct intersection * hit(struct intersections * xs)
   }
   return i;
 }
+
+
+inline static void intersections_sort(struct intersections * xs)
+{
+#define left_child(i) (2 * i + 1)
+
+  int start = xs->count / 2;
+  int end = xs->count;
+  while (end > 1) {
+    if (start > 0) {
+      start = start - 1;
+    } else {
+      end = end - 1;
+      struct intersection tmp = xs->i[0];
+      xs->i[0] = xs->i[end];
+      xs->i[end] = tmp;
+    }
+
+    int root = start;
+    while (left_child(root) < end) {
+      int child = left_child(root);
+      if (child + 1 < end && xs->i[child].t < xs->i[child+1].t) {
+        child = child + 1;
+      }
+      if (xs->i[root].t < xs->i[child].t) {
+        struct intersection tmp = xs->i[root];
+        xs->i[root] = xs->i[child];
+        xs->i[child] = tmp;
+        root = child;
+      } else {
+        break;
+      }
+    }
+  }
+
+#undef left_child
+}
+
+struct computations {
+  float t;
+  struct sphere const * object;
+  struct tuple point;
+  struct tuple eyev;
+  struct tuple normalv;
+  bool inside;
+};
+
+inline static struct computations prepare_computations(struct intersection intersection, struct ray ray)
+{
+  struct tuple point = ray_position(ray, intersection.t);
+  struct tuple eyev = tuple_neg(ray.direction);
+  struct tuple normalv = sphere_normal_at(intersection.object, point);
+
+  bool inside = false;
+  if (tuple_dot(normalv, eyev) < 0.0f) {
+    inside = true;
+    normalv = tuple_neg(normalv);
+  }
+
+  return (struct computations){
+    intersection.t,
+    intersection.object,
+    point,
+    eyev,
+    normalv,
+    inside
+  };
+}
diff --git a/test/run.sh b/test/run.sh
index 951be59..0851ac9 100644
--- a/test/run.sh
+++ b/test/run.sh
@@ -2,7 +2,7 @@
 
 set -eux
 
-for name in tuples canvas matrices transformations rays intersections spheres lights materials; do
+for name in tuples canvas matrices transformations rays intersections spheres lights materials world; do
     gcc -g -gdwarf-5 \
         -Wall -Werror -Wfatal-errors \
         -I. \
diff --git a/test/test_intersections.c b/test/test_intersections.c
index 84ed675..9ce984a 100644
--- a/test/test_intersections.c
+++ b/test/test_intersections.c
@@ -18,12 +18,13 @@ static bool intersections_test_0(const char ** scenario)
 
 static bool intersections_test_1(const char ** scenario)
 {
-  *scenario = "Aggregating intersections2";
+  *scenario = "Aggregating intersections";
 
   struct sphere s = sphere();
   struct intersection i1 = intersection(1.0f, &s);
   struct intersection i2 = intersection(2.0f, &s);
-  struct intersections2 xs = intersections2(i1, i2);
+  struct intersections xs;
+  intersections(&xs, 2, i1, i2);
 
   return
     xs.count == 2 &&
@@ -33,12 +34,13 @@ static bool intersections_test_1(const char ** scenario)
 
 static bool intersections_test_2(const char ** scenario)
 {
-  *scenario = "The hit, when all intersections2 have positive t";
+  *scenario = "The hit, when all intersections have positive t";
 
   struct sphere s = sphere();
   struct intersection i1 = intersection(1.0f, &s);
   struct intersection i2 = intersection(2.0f, &s);
-  struct intersections2 xs = intersections2(i2, i1);
+  struct intersections xs;
+  intersections(&xs, 2, i2, i1);
 
   struct intersection * i = hit((struct intersections *)&xs);
 
@@ -50,12 +52,13 @@ static bool intersections_test_2(const char ** scenario)
 
 static bool intersections_test_3(const char ** scenario)
 {
-  *scenario = "The hit, when some intersections2 have negative t";
+  *scenario = "The hit, when some intersections have negative t";
 
   struct sphere s = sphere();
   struct intersection i1 = intersection(-1.0f, &s);
   struct intersection i2 = intersection( 1.0f, &s);
-  struct intersections2 xs = intersections2(i2, i1);
+  struct intersections xs;
+  intersections(&xs, 2, i2, i1);
 
   struct intersection * i = hit((struct intersections *)&xs);
 
@@ -67,12 +70,13 @@ static bool intersections_test_3(const char ** scenario)
 
 static bool intersections_test_4(const char ** scenario)
 {
-  *scenario = "The hit, when all intersections2 have negative t";
+  *scenario = "The hit, when all intersections have negative t";
 
   struct sphere s = sphere();
   struct intersection i1 = intersection(-2.0f, &s);
   struct intersection i2 = intersection(-1.0f, &s);
-  struct intersections2 xs = intersections2(i2, i1);
+  struct intersections xs;
+  intersections(&xs, 2, i2, i1);
 
   struct intersection * i = hit((struct intersections *)&xs);
 
@@ -88,7 +92,8 @@ static bool intersections_test_5(const char ** scenario)
   struct intersection i2 = intersection( 7.0f, &s);
   struct intersection i3 = intersection(-3.0f, &s);
   struct intersection i4 = intersection( 2.0f, &s);
-  struct intersections4 xs = intersections4(i1, i2, i3, i4);
+  struct intersections xs;
+  intersections(&xs, 4, i1, i2, i3, i4);
 
   struct intersection * i = hit((struct intersections *)&xs);
 
@@ -98,6 +103,84 @@ static bool intersections_test_5(const char ** scenario)
     i->object == i4.object;
 }
 
+static bool intersections_test_6(const char ** scenario)
+{
+  *scenario = "In-place ascending sort of intersections";
+
+  struct sphere s1 = sphere();
+  s1.material.ambient = 1.0f;
+  struct sphere s2 = sphere();
+  s2.material.ambient = 2.0f;
+  struct sphere s3 = sphere();
+  s3.material.ambient = 3.0f;
+  struct sphere s4 = sphere();
+  s4.material.ambient = 4.0f;
+  struct intersection i1 = intersection( 5.0f, &s1);
+  struct intersection i2 = intersection( 7.0f, &s2);
+  struct intersection i3 = intersection(-3.0f, &s3);
+  struct intersection i4 = intersection( 2.0f, &s4);
+  struct intersections xs;
+  intersections(&xs, 4, i1, i2, i3, i4);
+
+  intersections_sort(&xs);
+
+  return
+    float_equal(xs.i[0].t, -3.0f) &&
+    float_equal(xs.i[0].object->material.ambient, 3.0f) &&
+    float_equal(xs.i[1].t, 2.0f) &&
+    float_equal(xs.i[1].object->material.ambient, 4.0f) &&
+    float_equal(xs.i[2].t, 5.0f) &&
+    float_equal(xs.i[2].object->material.ambient, 1.0f) &&
+    float_equal(xs.i[3].t, 7.0f) &&
+    float_equal(xs.i[3].object->material.ambient, 2.0f);
+}
+
+static bool intersections_test_7(const char ** scenario)
+{
+  *scenario = "Precomputing the state of an intersection";
+
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct sphere shape = sphere();
+  struct intersection i = intersection(4.0f, &shape);
+  struct computations comps = prepare_computations(i, r);
+
+  return
+    float_equal(comps.t, i.t) &&
+    comps.object == &shape &&
+    tuple_equal(comps.point, point(0.0f, 0.0f, -1.0f)) &&
+    tuple_equal(comps.eyev, vector(0.0f, 0.0f, -1.0f)) &&
+    tuple_equal(comps.normalv, vector(0.0f, 0.0f, -1.0f));
+}
+
+static bool intersections_test_8(const char ** scenario)
+{
+  *scenario = "The hit, when an intersection occurs on the outside";
+
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct sphere shape = sphere();
+  struct intersection i = intersection(4.0f, &shape);
+  struct computations comps = prepare_computations(i, r);
+
+  return
+    comps.inside == false;
+}
+
+static bool intersections_test_9(const char ** scenario)
+{
+  *scenario = "The hit, when an intersection occurs on the inside";
+
+  struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
+  struct sphere shape = sphere();
+  struct intersection i = intersection(1.0f, &shape);
+  struct computations comps = prepare_computations(i, r);
+
+  return
+    tuple_equal(comps.point, point(0.0f, 0.0f, 1.0f)) &&
+    tuple_equal(comps.eyev, vector(0.0f, 0.0f, -1.0f)) &&
+    comps.inside == true &&
+    tuple_equal(comps.normalv, vector(0.0f, 0.0f, -1.0f));
+}
+
 test_t intersections_tests[] = {
   intersections_test_0,
   intersections_test_1,
@@ -105,6 +188,10 @@ test_t intersections_tests[] = {
   intersections_test_3,
   intersections_test_4,
   intersections_test_5,
+  intersections_test_6,
+  intersections_test_7,
+  intersections_test_8,
+  intersections_test_9,
 };
 
 RUNNER(intersections_tests);
diff --git a/test/test_spheres.c b/test/test_spheres.c
index 5020da2..0a0afb5 100644
--- a/test/test_spheres.c
+++ b/test/test_spheres.c
@@ -14,7 +14,9 @@ static bool spheres_test_0(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -28,7 +30,9 @@ static bool spheres_test_1(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 1.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -42,7 +46,9 @@ static bool spheres_test_2(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 2.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return xs.count == 0;
 }
@@ -53,7 +59,9 @@ static bool spheres_test_3(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -67,7 +75,9 @@ static bool spheres_test_4(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 0.0f, 5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -81,7 +91,9 @@ static bool spheres_test_5(const char ** scenario)
 
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -117,7 +129,9 @@ static bool spheres_test_8(const char ** scenario)
   struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
   s.transform = scaling(2.0f, 2.0f, 2.0f);
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return
     xs.count == 2 &&
@@ -132,7 +146,9 @@ static bool spheres_test_9(const char ** scenario)
   struct ray r = ray(point(0.0f, 0.0f, 5.0f), vector(0.0f, 0.0f, 1.0f));
   struct sphere s = sphere();
   s.transform = translation(5.0f, 0.0f, 0.0f);
-  struct intersections2 xs = intersect(&s, r);
+  struct intersections xs;
+  xs.count = 0;
+  intersect(&s, r, &xs);
 
   return xs.count == 0;
 }
diff --git a/test/test_world.c b/test/test_world.c
new file mode 100644
index 0000000..24bec0d
--- /dev/null
+++ b/test/test_world.c
@@ -0,0 +1,135 @@
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "world.h"
+#include "runner.h"
+
+static bool world_test_0(const char ** scenario)
+{
+  *scenario = "Creating a world";
+
+  struct world w = world();
+
+  return
+    w.object_count == 0 &&
+    tuple_equal(w.light.intensity, tuple(0.0f, 0.0f, 0.0f, 0.0f));
+}
+
+static bool world_test_1(const char ** scenario)
+{
+  *scenario = "The default world";
+
+  struct light light = point_light(point(-10.0f, 10.0f, -10.0f), color(1.0f, 1.0f, 1.0f));
+  struct sphere s1 = sphere();
+  s1.material.color = color(0.8f, 1.0f, 0.6f);
+  s1.material.diffuse = 0.7f;
+  s1.material.specular = 0.2f;
+  struct sphere s2 = sphere();
+  s2.transform = scaling(0.5f, 0.5f, 0.5f);
+  struct world w = default_world();
+  return
+    tuple_equal(w.light.position, light.position) &&
+    tuple_equal(w.light.intensity, light.intensity) &&
+    w.object_count == 2 &&
+    tuple_equal(w.objects[0].material.color, s1.material.color) &&
+    float_equal(w.objects[0].material.diffuse, s1.material.diffuse) &&
+    float_equal(w.objects[0].material.specular, s1.material.specular) &&
+    mat4x4_equal(&w.objects[1].transform, &s2.transform);
+}
+
+static bool world_test_2(const char ** scenario)
+{
+  *scenario = "Intersect a world with a ray";
+
+  struct world w = default_world();
+
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct intersections xs;
+  intersect_world(&w, r, &xs);
+
+  return
+    xs.count == 4 &&
+    float_equal(xs.i[0].t, 4.0f) &&
+    float_equal(xs.i[1].t, 4.5f) &&
+    float_equal(xs.i[2].t, 5.5f) &&
+    float_equal(xs.i[3].t, 6.0f);
+}
+
+static bool world_test_3(const char ** scenario)
+{
+  *scenario = "Shading an intersection";
+
+  struct world w = default_world();
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct sphere * shape = &w.objects[0];
+  struct intersection i = intersection(4.0f, shape);
+  struct computations comps = prepare_computations(i, r);
+  struct tuple c = shade_hit(&w, &comps);
+
+  return tuple_equal(c, color(0.38066, 0.47583, 0.2855));
+}
+
+static bool world_test_4(const char ** scenario)
+{
+  *scenario = "Shading an intersection from the inside";
+
+  struct world w = default_world();
+  w.light = point_light(point(0.0f, 0.25f, 0.0f), color(1.0f, 1.0f, 1.0f));
+  struct ray r = ray(point(0.0f, 0.0f, 0.0f), vector(0.0f, 0.0f, 1.0f));
+  struct sphere * shape = &w.objects[1];
+  struct intersection i = intersection(0.5f, shape);
+  struct computations comps = prepare_computations(i, r);
+  struct tuple c = shade_hit(&w, &comps);
+
+  return tuple_equal(c, color(0.90498, 0.90498, 0.90498));
+}
+
+static bool world_test_5(const char ** scenario)
+{
+  *scenario = "The color when a ray misses";
+
+  struct world w = default_world();
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 1.0f, 0.0f));
+  struct tuple c = color_at(&w, r);
+
+  return tuple_equal(c, color(0.0f, 0.0f, 0.0f));
+}
+
+static bool world_test_6(const char ** scenario)
+{
+  *scenario = "The color when a ray hits";
+
+  struct world w = default_world();
+  struct ray r = ray(point(0.0f, 0.0f, -5.0f), vector(0.0f, 0.0f, 1.0f));
+  struct tuple c = color_at(&w, r);
+
+  return tuple_equal(c, color(0.38066f, 0.47583f, 0.2855f));
+}
+
+static bool world_test_7(const char ** scenario)
+{
+  *scenario = "The color with an intersection behind the ray";
+
+  struct world w = default_world();
+  struct sphere * outer = &w.objects[0];
+  outer->material.ambient = 1.0f;
+  struct sphere * inner = &w.objects[1];
+  inner->material.ambient = 1.0f;
+  struct ray r = ray(point(0.0f, 0.0f, 0.75f), vector(0.0f, 0.0f, -1.0f));
+  struct tuple c = color_at(&w, r);
+
+  return tuple_equal(c, inner->material.color);
+}
+
+test_t world_tests[] = {
+  world_test_0,
+  world_test_1,
+  world_test_2,
+  world_test_3,
+  world_test_4,
+  world_test_5,
+  world_test_6,
+  world_test_7,
+};
+
+RUNNER(world_tests)
diff --git a/world.h b/world.h
new file mode 100644
index 0000000..07fb490
--- /dev/null
+++ b/world.h
@@ -0,0 +1,73 @@
+#pragma once
+
+#include "lights.h"
+#include "spheres.h"
+#include "transformations.h"
+#include "intersections.h"
+#include "rays.h"
+#include "materials.h"
+
+#define WORLD_MAX_OBJECTS 128
+
+struct world {
+  struct light light;
+  int object_count;
+  struct sphere objects[WORLD_MAX_OBJECTS];
+};
+
+inline static struct world world()
+{
+  return (struct world){
+    .light = (struct light){{{{0}}}},
+    .object_count = 0,
+  };
+}
+
+inline static struct world default_world()
+{
+  struct sphere s1 = sphere();
+  s1.material.color = color(0.8f, 1.0f, 0.6f);
+  s1.material.diffuse = 0.7f;
+  s1.material.specular = 0.2f;
+  struct sphere s2 = sphere();
+  s2.transform = scaling(0.5f, 0.5f, 0.5f);
+
+  return (struct world){
+    .light = point_light(point(-10.0f, 10.0f, -10.0f), color(1.0f, 1.0f, 1.0f)),
+    .object_count = 2,
+    .objects = { s1, s2 }
+  };
+}
+
+inline static void intersect_world(struct world * world, struct ray ray, struct intersections * intersections)
+{
+  intersections->count = 0;
+  for (int i = 0; i < world->object_count; i++) {
+    intersect(&world->objects[i], ray, intersections);
+  }
+  intersections_sort(intersections);
+}
+
+inline static struct tuple shade_hit(struct world * world, struct computations * computations)
+{
+  struct tuple color = lighting(computations->object->material,
+                                world->light,
+                                computations->point,
+                                computations->eyev,
+                                computations->normalv);
+  return color;
+}
+
+inline static struct tuple color_at(struct world * world, struct ray ray)
+{
+  struct intersections xs;
+  intersect_world(world, ray, &xs);
+  if (xs.count >= 1) {
+    struct intersection i = *hit(&xs);
+    struct computations computations = prepare_computations(i, ray);
+    struct tuple color = shade_hit(world, &computations);
+    return color;
+  } else {
+    return color(0.0f, 0.0f, 0.0f);
+  }
+}