add option to change probability of sampling lights

include/raytracing.h

@@ -34,7 +34,7 @@ typedef struct Camera {
   Vec3 w;
   Vec3 dof_disc_u;
   Vec3 dof_disc_v;
-  bool importance_sampling;
+  float lights_sampling_prob;
 } Camera;
 
 void Camera_init(Camera *camera);

src/main.c

@@ -279,7 +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;
+  camera.lights_sampling_prob = 0.5f;
 
   if (argc > 3)
     camera.img_width = strtol(argv[2], NULL, 10);

src/material.c

@@ -36,19 +36,19 @@ static Vec3 rand_cosine_theta(PCG32 *rng) {
   float phi = 2.0f * (float)M_PI * r1;
   return vec3(cosf(phi) * sqrtf(r2), sinf(phi) * sqrtf(r2), sqrtf(1.0f - r2));
 }
+static float Lambertian_scattering_pdf(const HitRecord *rec, Vec3 r_in, Vec3 r_out) {
+  float cos_theta = vec3_dot(rec->normal, vec3_normalize(r_out));
+  return cos_theta < 0.0f ? 0.0f : cos_theta / (float)M_PI;
+}
 static bool Lambertian_scatter(const HitRecord *rec, Vec3 r_in, Vec3 *r_out, Vec3 *color, float *pdf, PCG32 *rng) {
   ONB onb;
   ONB_from_w(&onb, rec->normal);
 
   *r_out = ONB_local(&onb, rand_cosine_theta(rng));
   *color = _Texture_value(rec);
-  *pdf = vec3_dot(onb.w, vec3_normalize(*r_out)) / (float)M_PI; // cos(theta) / pi
+  *pdf = Lambertian_scattering_pdf(rec, r_in, *r_out);
   return true;
 }
-static float Lambertian_scattering_pdf(const HitRecord *rec, Vec3 r_in, Vec3 r_out) {
-  float cos_theta = vec3_dot(rec->normal, vec3_normalize(r_out));
-  return cos_theta < 0.0f ? 0.0f : cos_theta / (float)M_PI;
-}
 static MaterialVTable LAMBERTIAN_VTABLE = {Lambertian_scatter, Lambertian_scattering_pdf, Empty_emit};
 void Lambertian_init(Material *self, Texture *albedo) {
   self->vtable = &LAMBERTIAN_VTABLE;

src/raytracing.c

@@ -51,11 +51,12 @@ static Vec3 Camera_ray_color(const Camera *camera, const Ray *ray, const World *
       return emission_color;
 
     // mixture pdf
-    if (camera->importance_sampling) {
+    float prob = camera->lights_sampling_prob;
+    if (prob > 0.0f) {
       const Hittable *lights = &world->lights.hittable;
-      if (pcg32_f32(rng) < 0.5f) // change scatter ray towards the light half of the time
+      if (pcg32_f32(rng) < prob) // change scatter ray towards the light
         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
+      pdf = (1.0f - prob) * pdf + prob * lights->vtable->pdf(lights, &new_ray, rng); // update pdf
     }
 
     // spawn new ray