Add uniform cone sampling

src/render.cpp

@@ -132,7 +132,7 @@ Vec3 cast_ray(World *world, Ray *r, int cur_depth) {
         }
         indirect_lighting = rwm_v3_scalar_div(indirect_lighting, (float) NUM_PT_SAMPLES * pdf);
 #endif // #if USE_GLOBAL_ILLUMINATION
-        // Finally multiply by lambertian brdf
+        // Finally multiply by lambertian BRDF
         color = (direct_lighting + rwm_v3_scalar_div(indirect_lighting, pdf)) * rwm_v3_scalar_div(ii.material->albedo, PI);
         if (ii.material->use_texture) {
           color *= get_checkerboard(ii.tex_coord);

src/sampling.cpp

@@ -64,6 +64,17 @@ Point2 concentric_sample_disk(Point2 u) {
   return r * rwm_v2_init(cosf(theta), sinf(theta));
 }
 
+Vec3 uniform_sample_cone(Point2 u, float cos_theta_max) {
+  float cos_theta = (1 - u.e[0]) + u.e[0] * cos_theta_max;
+  float sin_theta = rwm_sqrt(1 - SQUARE(cos_theta));
+  float phi = u.e[1] * 2 * PI;
+  return rwm_v3_init(cosf(phi) * sin_theta, sinf(phi) * sin_theta, cos_theta);
+}
+
+float uniform_cone_pdf(float cos_theta_max) {
+  return 1/(2 * PI * (1 - cos_theta_max));
+}
+
 void stratified_sample_1d(float *out_samples, int n_samples, bool jitter) {
   float inv_n_samples = 1.0f/n_samples;
   for (int i = 0; i < n_samples; i++) {

src/sampling.h

@@ -16,6 +16,9 @@ float cosine_hemisphere_pdf(float cos_theta);
 Point2 uniform_sample_disk(Point2 u);
 Point2 concentric_sample_disk(Point2 u);
 
+Vec3 uniform_sample_cone(Point2 u, float cos_theta_max);
+float uniform_cone_pdf(float cos_theta_max);
+
 void stratified_sample_1d(float *out_samples, int n_samples, bool jitter);
 void stratified_sample_2d(Point2 *out_samples, int nx, int ny, bool jitter);