Add defocus blur

camera.c

@@ -6,29 +6,38 @@
 #include <math.h>
 
 void camera_init(Camera *camera, Point3 look_from, Point3 look_at, Vec3 up,
-                 double vertical_fov, double aspect_ratio) {
+                 double vertical_fov, double aspect_ratio, double aperture,
+                 double focus_distance) {
   double theta = degrees_to_radians(vertical_fov);
   double h = tan(theta / 2.0);
   double viewport_height = 2.0 * h;
   double viewport_width = aspect_ratio * viewport_height;
 
-  Vec3 w = vec3_normalize(point3_sub(look_from, look_at));
-  Vec3 u = vec3_normalize(vec3_cross(up, w));
-  Vec3 v = vec3_cross(w, u);
+  camera->w = vec3_normalize(point3_sub(look_from, look_at));
+  camera->u = vec3_normalize(vec3_cross(up, camera->w));
+  camera->v = vec3_cross(camera->w, camera->u);
 
   camera->origin = look_from;
-  camera->horizontal = vec3_mul(viewport_width, u);
-  camera->vertical = vec3_mul(viewport_height, v);
+  camera->horizontal = vec3_mul(focus_distance * viewport_width, camera->u);
+  camera->vertical = vec3_mul(focus_distance * viewport_height, camera->v);
   Vec3 offset =
       vec3_add(vec3_div(camera->horizontal, 2), vec3_div(camera->vertical, 2));
-  offset = vec3_add(offset, w);
+  offset = vec3_add(offset, vec3_mul(focus_distance, camera->w));
   camera->lower_left_corner = point3_add(camera->origin, vec3_neg(offset));
+
+  camera->lens_radius = aperture / 2.0;
 }
 
 Ray camera_get_ray(const Camera *camera, double s, double t) {
+  Vec3 rd = vec3_mul(camera->lens_radius, vec3_random_in_unit_disk());
+  Vec3 offset = vec3_add(vec3_mul(rd.x, camera->u), vec3_mul(rd.y, camera->v));
+
   Point3 screen_point = point3_add(
       camera->lower_left_corner,
       vec3_add(vec3_mul(s, camera->horizontal), vec3_mul(t, camera->vertical)));
   Vec3 direction = point3_sub(screen_point, camera->origin);
-  return (Ray){camera->origin, direction};
+  return (Ray){
+      point3_add(camera->origin, offset),
+      vec3_sub(direction, offset),
+  };
 }

camera.h

@@ -10,10 +10,13 @@ typedef struct Camera {
   Point3 lower_left_corner;
   Vec3 horizontal;
   Vec3 vertical;
+  Vec3 u, v, w;
+  double lens_radius;
 } Camera;
 
 void camera_init(Camera *camera, Point3 look_from, Point3 look_at, Vec3 up,
-                 double vertical_fov, double aspect_ratio);
+                 double vertical_fov, double aspect_ratio, double aperture,
+                 double focus_distance);
 
 Ray camera_get_ray(const Camera *camera, double s, double t);
 

main.c

@@ -90,9 +90,16 @@ int main(void) {
   hittable_list_add(&world, (const Hittable *)&sphere_right);
 
   /* Camera */
+
+  Point3 look_from = {3.0, 3.0, 2.0};
+  Point3 look_at = {0.0, 0.0, -1.0};
+  Vec3 up = {0.0, 1.0, 0.0};
+  double dist_to_focus = vec3_length(point3_sub(look_from, look_at));
+  double aperture = 2.0;
+
   Camera camera;
-  camera_init(&camera, (Point3){-2.0, 2.0, 1.0}, (Point3){0.0, 0.0, -1.0},
-              (Vec3){0.0, 1.0, 0.0}, 20, aspect_ratio);
+  camera_init(&camera, look_from, look_at, up, 20, aspect_ratio, aperture,
+              dist_to_focus);
 
   printf("P3\n%u %u\n255\n", image_width, image_height);
 

vec3.c

@@ -52,9 +52,19 @@ Vec3 vec3_random_in_range(double min, double max) {
 }
 
 Vec3 vec3_random_in_unit_sphere(void) {
-  while (1) {
-    Vec3 result = vec3_random_in_range(-1, 1);
-    if (vec3_length2(result) >= 1)
+  while (true) {
+    Vec3 result = vec3_random_in_range(-1.0, 1.0);
+    if (vec3_length2(result) >= 1.0)
+      continue;
+    return result;
+  }
+}
+
+Vec3 vec3_random_in_unit_disk(void) {
+  while (true) {
+    Vec3 result = (Vec3){random_double_in_range(-1.0, 1.0),
+                         random_double_in_range(-1.0, 1.0), 0.0};
+    if (vec3_length2(result) >= 1.0)
       continue;
     return result;
   }

vec3.h

@@ -24,6 +24,7 @@ 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);
+Vec3 vec3_random_in_unit_disk(void);
 Vec3 vec3_random_unit_vector(void);
 
 bool vec3_is_near_zero(Vec3 v);