add scattering pdf and sampling for HittableList. add option to chang…

…e sampling behavior

include/raytracing.h

@@ -8,7 +8,7 @@
 
 typedef struct World {
   HittableList objects;
-  Hittable *light;
+  HittableList lights;
 } World;
 
 void World_init(World *world, size_t max_objects);
@@ -34,6 +34,7 @@ typedef struct Camera {
   Vec3 w;
   Vec3 dof_disc_u;
   Vec3 dof_disc_v;
+  bool importance_sampling;
 } Camera;
 
 void Camera_init(Camera *camera);

src/hittable.c

@@ -85,7 +85,26 @@ static bool HittableList_hit(const Hittable *self_, const Ray *ray, float t_min,
 
   return hit_anything;
 }
-static HittableVTable HITTABLE_LIST_VTABLE = {HittableList_hit};
+static float HittableList_pdf(const Hittable *self_, const Ray *ray, PCG32 *rng) {
+  const HittableList *self = (const HittableList *)self_;
+  float pdf = 0.0f;
+  float count = 0.0f;
+  for (int i = 0; i < self->size; i++) {
+    if (self->items[i]->vtable->pdf != NULL) { // TODO: remove this when all hittables implement pdf
+      pdf += self->items[i]->vtable->pdf(self->items[i], ray, rng);
+      count += 1.0f;
+    }
+  }
+  return pdf / fmaxf(count, 1.0f);
+}
+static Vec3 HittableList_rand(const Hittable *self_, Vec3 origin, PCG32 *rng) {
+  const HittableList *self = (const HittableList *)self_;
+  Hittable *obj = self->items[pcg32_u32_between(rng, 0, self->size)];
+  if (obj->vtable->rand == NULL)
+    return HittableList_rand(self_, origin, rng); // rejection sampling
+  return obj->vtable->rand(obj, origin, rng);
+}
+static HittableVTable HITTABLE_LIST_VTABLE = {HittableList_hit, HittableList_pdf, HittableList_rand};
 void HittableList_init(HittableList *self, size_t max_size) {
   *self =
       (HittableList){{&HITTABLE_LIST_VTABLE, AABB_EMPTY}, max_size, 0, my_malloc(sizeof(self->items[0]) * max_size)};

src/main.c

@@ -135,8 +135,15 @@ void scene_simple_light(World *world, Camera *camera) {
   Material *light = DiffuseLight_new(Solid_new(vec3(4, 4, 4)));
   HittableList_append(&world->objects, Sphere_new(vec3(0, -1000, 0), 1000, perlin));
   HittableList_append(&world->objects, Sphere_new(vec3(0, 2, 0), 2, perlin));
-  HittableList_append(&world->objects, Sphere_new(vec3(0, 7, 0), 2, light));
-  HittableList_append(&world->objects, Quad_new(vec3(3, 1, -2), vec3(2, 0, 0), vec3(0, 2, 0), light));
+
+  Hittable *light_src;
+  light_src = Quad_new(vec3(3, 1, -2), vec3(2, 0, 0), vec3(0, 2, 0), light);
+  HittableList_append(&world->objects, light_src);
+  HittableList_append(&world->lights, light_src);
+
+  light_src = Sphere_new(vec3(0, 7, 0), 2, light);
+  HittableList_append(&world->objects, light_src);
+  HittableList_append(&world->lights, light_src);
 
   camera->vfov = 20.0f;
   camera->background = VEC3_ZERO;
@@ -160,7 +167,7 @@ void scene_cornell_box(World *world, Camera *camera) {
 
   Hittable *light_src = Quad_new(vec3(343, 554, 332), vec3(-130, 0, 0), vec3(0, 0, -105), light);
   HittableList_append(&world->objects, light_src);
-  world->light = light_src;
+  HittableList_append(&world->lights, light_src);
 
   Hittable *box1 = Box_new(vec3(0, 0, 0), vec3(165, 330, 165), white);
   box1 = RotateY_new(box1, 15);
@@ -272,6 +279,7 @@ int main(int argc, char *argv[]) {
   camera.vup = vec3(0, 1, 0);
   camera.dof_angle = 0.0f;
   camera.focal_length = 10.0f;
+  camera.importance_sampling = true;
 
   if (argc > 3)
     camera.img_width = strtol(argv[2], NULL, 10);

src/raytracing.c

@@ -3,7 +3,10 @@
 #include <math.h>
 #include <stdio.h>
 
-void World_init(World *world, size_t max_objects) { HittableList_init(&world->objects, max_objects); }
+void World_init(World *world, size_t max_objects) {
+  HittableList_init(&world->objects, max_objects);
+  HittableList_init(&world->lights, max_objects);
+}
 
 void Camera_init(Camera *camera) {
   camera->img_height = (int)((float)camera->img_width / camera->aspect_ratio);
@@ -48,10 +51,11 @@ static Vec3 Camera_ray_color(const Camera *camera, const Ray *ray, const World *
       return emission_color;
 
     // mixture pdf
-    if (world->light != NULL) {
+    if (camera->importance_sampling) {
+      const Hittable *lights = &world->lights.hittable;
       if (pcg32_f32(rng) < 0.5f) // change scatter ray towards the light half of the time
-        new_ray.direction = world->light->vtable->rand(world->light, rec.p, rng);
-      pdf = 0.5f * pdf + 0.5f * world->light->vtable->pdf(world->light, &new_ray, rng); // update pdf
+        new_ray.direction = lights->vtable->rand(lights, rec.p, rng);
+      pdf = 0.5f * pdf + 0.5f * lights->vtable->pdf(lights, &new_ray, rng); // update pdf
     }
 
     // spawn new ray