feat: impl random sampling instead of point light algorithm

Random sampling is available when building with `-DRANDOM_SAMPLING', or with
`make randsampl'.

The sample counts are rather low, so the output is both slow and noisy, which is
why it's disabled by default.

Makefile

@@ -19,11 +19,15 @@ bin/raytracer: $(OBJ_FILES)
 	@mkdir -p $(OBJ_DIR)
 	$(CXX) $(CXXFLAGS) -o $@ $^
 
+.PHONY: randsampl
+randsampl: CXXFLAGS += -DRANDOM_SAMPLING
+randsampl: bin/raytracer
+
 .PHONY: debug
 debug: CXXFLAGS += -O0 -g
 debug: clean bin/raytracer
 
 .PHONY: clean
 clean:
-	$(RM) -r obj/*.o
-	$(RM) bin/*
+	$(RM) obj/*.o
+	$(RM) bin/raytracer

README

@@ -9,6 +9,7 @@ The raytracer implements the following:
  - IOR-based refraction
  - Cook-Torrance BRDF (a few other models are left in the code)
  - Primitive object materials
+ - Random sampling (build with `make randsampl' to add fireflies :)
 
 You can move around with WASD and SPC/Z; zoom with I/O, change the exposure with
 +/-, and quit with Q.

src/raytrace.cpp

@@ -1,7 +1,36 @@
 #include "../include/raytrace.hpp"
 #include "../include/objects.hpp"
 #include <math.h>
+
+#ifdef RANDOM_SAMPLING
 #include <random>
+#endif
+
+#ifdef RANDOM_SAMPLING
+#define MAX(l, r) ((l) < (r)) ? (r) : (l)
+#define MIN(l, r) ((r) < (l)) ? (r) : (l)
+
+static inline v3 generate_normal(const v3 &v)
+{
+    struct h {
+	choice_t x;
+	unsigned n;
+	bool operator<(const h& r) { return x < r.x; }
+    };
+
+    h one{v.x, 1}, two{v.y, 2}, three{v.z, 3};
+    auto max = MAX(one, MAX(two, three));
+    auto min = MIN(one, MAX(two, three));
+    unsigned middle = 6 - max.n - min.n;
+
+    v3 normal;
+    normal.c[max.n] = normal.c[middle];
+    normal.c[middle] = -max.x;
+    normal.c[min.n] = 0;
+
+    return normal;
+}
+#endif
 
 Renderable::Renderable(const Material& specs) : specs(specs) {}
 
@@ -33,6 +62,12 @@ Renderable* shoot_ray_into_objects(const v3& eye, const v3& dir, const std::vect
     return hit_object;
 }
 
+#ifdef RANDOM_SAMPLING
+std::random_device rd;
+std::mt19937 gen(rd());
+std::uniform_real_distribution<> dis(0.0, 1.0);
+#endif
+
 v3 ray_trace(const v3& eye, const v3& dir,
 	     const std::vector<Renderable*>& scene,
 	     const std::vector<Renderable*>& objects,
@@ -56,7 +91,6 @@ v3 ray_trace(const v3& eye, const v3& dir,
 	colour += ((Light*)hit_obj)->specs.colour * 8 * kDistance;
 	if(depth > 0) colour += ray_trace(eye, dir, scene, objects, lights, depth - 1, l) * (1 - kDistance);
     }  else if (hit_type > 0) {
-	// Figure out which lights are visible from the hit location
 	choice_t dist;
 	v3 loc, normal;
 	v3 light_dir;
@@ -64,22 +98,47 @@ v3 ray_trace(const v3& eye, const v3& dir,
 
 	Light *l = nullptr;
 
+	// Figure out which lights are visible from the hit location
 	for (auto* _l : lights) {
 	    l = (Light *)_l;
 	    const v3 to_light = l->o - hit_loc;
 	    light_dir = to_light.norm();
 	    dist = to_light.len();
-	    shoot_ray_into_objects(hit_loc, light_dir, objects,
-				   dist, loc, normal, type, hit_obj);
 
-	    // We hit the light directly: shade the pixel.
-	    if (type == -1) {
-		const choice_t kDistance = to_light.lensquared() / 1000;
-		colour += cook_torrance(dir, hit_normal, light_dir, hit_obj->specs.specular,
-					hit_obj->specs.roughness, hit_obj->specs.ior,
-					hit_obj->specs.colour, l->specs.colour)
-		    * (1 - hit_obj->specs.transparency) / kDistance;
+	    v3 sample_dir = light_dir;
+#ifndef RANDOM_SAMPLING
+	    constexpr const int SAMPLE_COUNT = 1;
+#endif
+
+#ifdef RANDOM_SAMPLING
+	    v3 disc_n1 = generate_normal(light_dir).norm();
+	    v3 disc_n2 = disc_n1.cross(light_dir);
+	    choice_t cone_angle = asin(l->r / sqrt(l->r*l->r + dist*dist));
+
+	    constexpr const int SAMPLE_COUNT = 5;
+
+	    for(int i = 0; i < SAMPLE_COUNT; ++i) {
+		choice_t phi = dis(gen) * 2 * M_PI;
+		choice_t r   = sqrt(dis(gen)) * l->r;
+
+		sample_dir = (((disc_n1 * cos(phi) + disc_n2 * sin(phi)) * r) + to_light).norm();
+#endif
+
+		shoot_ray_into_objects(hit_loc, sample_dir, objects,
+				       dist, loc, normal, type, hit_obj);
+
+		// We hit the light: shade the pixel.
+		if (type == -1) {
+		    const choice_t kDistance = to_light.lensquared() / 1000;
+		    colour += cook_torrance(dir, hit_normal, light_dir, hit_obj->specs.specular,
+					    hit_obj->specs.roughness, hit_obj->specs.ior,
+					    hit_obj->specs.colour, l->specs.colour)
+			* (1 - hit_obj->specs.transparency) / (kDistance * SAMPLE_COUNT);
+		}
+
+#ifdef RANDOM_SAMPLING
 	    }
+#endif
 	}
 
 	// Add the colour from the reflection, if we have enough depth
@@ -99,17 +158,18 @@ v3 ray_trace(const v3& eye, const v3& dir,
             }
         }
 
-	// // Random sample
-	// std::random_device rd;
-	// std::mt19937 gen(rd());
-	// std::uniform_real_distribution<> dis(0.0, 1.0);
-	// const v3 y = hit_normal.cross(dir);
-	// for(int i = 0; i < 2; ++i) {
-	//     const v3 sample_dir = (hit_normal + dir * dis(gen) + y * dis(gen)).norm();
-	//     choice_t dist = 1;
-	//     const v3 hit_colour = ray_trace(hit_loc, sample_dir, scene, objects, lights, 0, hit_obj, &dist);
-	//     colour += hit_colour / (dist * dist);
-	// }
+
+#ifdef RANDOM_SAMPLING
+	if(kReflectionAtt > 1e-4 && depth > 0) {
+	    const v3 y = hit_normal.cross(dir);
+	    for(int i = 0; i < 3; ++i) {
+		const v3 sample_dir = (hit_normal + dir * dis(gen) + y * dis(gen)).norm();
+		const v3 hit_colour = ray_trace(hit_loc, sample_dir, scene, objects, lights, 0, hit_obj, &dist);
+		colour += hit_colour * kReflectionAtt / 3;
+	    }
+	}
+#endif
+
     }
 
     return colour;