RayTracing · hollasch · Apr 15, 2021 · Apr 13, 2021 · Apr 13, 2021 · Apr 14, 2021
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -22,6 +22,7 @@ Change Log -- Ray Tracing in One Weekend
   - Change: general rename of `mat_ptr` to `mat` (material)
   - Change: hittable::bounding_box() signature has changed to always return a value (#859)
   - Fix: Enabled compiler warnings for MSVC, Clang, GNU. Cleaned up warnings as fit (#865)
+  - Change: replaced random vector in `isotropic` with `random_unit_vector`
 
 ### In One Weekend
   - Added: More commentary about the choice between `double` and `float` (#752)
@@ -35,7 +36,9 @@ Change Log -- Ray Tracing in One Weekend
   - Fix: Fixed `bvh_node` constructor definition signature (#872)
 
 ### The Rest of Your Life
+  - Fix: Added missing functionality for `isotropic` (#664)
   - Fix: Variable `direction` was used without being defined in listing 11 (#831)
+  - Fix: Added missing functionality for `isotropic` (#664)
 
 
 ----------------------------------------------------------------------------------------------------

diff --git a/books/RayTracingTheNextWeek.html b/books/RayTracingTheNextWeek.html
@@ -3145,7 +3145,7 @@
 
         bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
         const override {
-            scattered = ray(rec.p, random_in_unit_sphere(), r_in.time());
+            scattered = ray(rec.p, random_unit_vector(), r_in.time());
             attenuation = albedo->value(rec.u, rec.v, rec.p);
             return true;
         }

diff --git a/books/RayTracingTheRestOfYourLife.html b/books/RayTracingTheRestOfYourLife.html
@@ -2143,6 +2143,7 @@
     class lambertian : public material {
       public:
         ...
+
         bool scatter(
             const ray& r_in, const hit_record& rec, color& alb, ray& scattered, double& pdf
         ) const override {
@@ -2158,6 +2159,9 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
             return true;
         }
+
+        ...
+    }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [scatter-onb]: <kbd>[material.h]</kbd> Scatter function, with orthonormal basis]
 </div>
@@ -2171,6 +2175,44 @@
 Let’s get rid of some of that noise.
 </div>
 
+<div class='together'>
+But first, let's quickly update the `isotropic` material:
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    class isotropic : public material {
+      public:
+        isotropic(color c) : albedo(make_shared<solid_color>(c)) {}
+        isotropic(shared_ptr<texture> a) : albedo(a) {}
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        bool scatter(
+            const ray& r_in, const hit_record& rec, color& alb, ray& scattered, double& pdf
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+        ) const override {
+            scattered = ray(rec.p, random_unit_vector(), r_in.time());
+            attenuation = albedo->value(rec.u, rec.v, rec.p);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+            pdf = 1 / (4 * pi);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+            return true;
+        }
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        double scattering_pdf(const ray& r_in, const hit_record& rec, const ray& scattered)
+        const override {
+            return 1 / (4 * pi);
+        }
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+
+        public:
+        shared_ptr<texture> albedo;
+    };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [class-isotropic-impsample]: <kbd>[material.h]</kbd>
+    Isotropic material, modified for importance sampling]
+</div>
 
 
 Sampling Lights Directly
@@ -2438,8 +2480,26 @@
 </div>
 
 <div class='together'>
-We’ll see if we need to add anything else to `pdf` by fleshing out the subclasses. First, let’s try
-a cosine density:
+We’ll see if we need to add anything else to `pdf` by fleshing out the subclasses. First, we'll
+create a uniform density over the unit sphere:
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    class sphere_pdf : public pdf {
+        public:
+          sphere_pdf() { }
+
+          double value(const vec3& direction) const override {
+              return 1/ (4 * pi);
+          }
+
+          vec3 generate() const override {
+              return random_unit_vector();
+          }
+      };
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [class-uni-pdf]: <kbd>[pdf.h]</kbd> The uniform_pdf class]
+
+Next, let’s try a cosine density:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class cosine_pdf : public pdf {
@@ -2903,14 +2963,15 @@
 </div>
 
 <div class='together'>
-The Lambertian material becomes simpler:
+The `lambertian` material becomes simpler:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class lambertian : public material {
       public:
         lambertian(const color& a) : albedo(make_shared<solid_color>(a)) {}
         lambertian(shared_ptr<texture> a) : albedo(a) {}
 
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
         bool scatter(const ray& r_in, const hit_record& rec, scatter_record& srec) const override {
             srec.attenuation = albedo->value(rec.u, rec.v, rec.p);
@@ -2932,6 +2993,38 @@
     [Listing [lambertian-scatter]: <kbd>[material.h]</kbd> New lambertian scatter() method]
 </div>
 
+<div class='together'>
+As does the `isotropic` material:
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    class isotropic : public material {
+        public:
+        isotropic(color c) : albedo(make_shared<solid_color>(c)) {}
+        isotropic(shared_ptr<texture> a) : albedo(a) {}
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        bool scatter(const ray& r_in, const hit_record& rec, scatter_record& srec) const override {
+            srec.attenuation = albedo->value(rec.u, rec.v, rec.p);
+            srec.pdf_ptr = make_shared<sphere_pdf>();
+            srec.skip_pdf = false;
+            return true;
+        }
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+
+
+        double scattering_pdf(const ray& r_in, const hit_record& rec, const ray& scattered)
+        const override {
+            return 1 / (4 * pi);
+        }
+
+        public:
+        shared_ptr<texture> albedo;
+    };
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [isotropic-scatter]: <kbd>[material.h]</kbd> New isotropic scatter() method]
+</div>
+
 <div class='together'>
 And `ray_color()` changes are small:
 

diff --git a/src/TheNextWeek/material.h b/src/TheNextWeek/material.h
@@ -136,7 +136,7 @@ class isotropic : public material {
 
     bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
     const override {
-        scattered = ray(rec.p, random_in_unit_sphere(), r_in.time());
+        scattered = ray(rec.p, random_unit_vector(), r_in.time());
         attenuation = albedo->value(rec.u, rec.v, rec.p);
         return true;
     }

diff --git a/src/TheRestOfYourLife/constant_medium.h b/src/TheRestOfYourLife/constant_medium.h
@@ -0,0 +1,87 @@
+#ifndef CONSTANT_MEDIUM_H
+#define CONSTANT_MEDIUM_H
+//==============================================================================================
+// Originally written in 2016 by Peter Shirley <ptrshrl@gmail.com>
+//
+// To the extent possible under law, the author(s) have dedicated all copyright and related and
+// neighboring rights to this software to the public domain worldwide. This software is
+// distributed without any warranty.
+//
+// You should have received a copy (see file COPYING.txt) of the CC0 Public Domain Dedication
+// along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
+//==============================================================================================
+
+#include "rtweekend.h"
+
+#include "hittable.h"
+#include "material.h"
+#include "texture.h"
+
+
+class constant_medium : public hittable {
+  public:
+    constant_medium(shared_ptr<hittable> b, double d, shared_ptr<texture> a)
+      : boundary(b), neg_inv_density(-1/d), phase_function(make_shared<isotropic>(a))
+    {}
+
+    constant_medium(shared_ptr<hittable> b, double d, color c)
+      : boundary(b), neg_inv_density(-1/d), phase_function(make_shared<isotropic>(c))
+    {}
+
+    bool hit(const ray& r, interval ray_t, hit_record& rec) const override {
+        // Print occasional samples when debugging. To enable, set enableDebug true.
+        const bool enableDebug = false;
+        const bool debugging = enableDebug && random_double() < 0.00001;
+
+        hit_record rec1, rec2;
+
+        if (!boundary->hit(r, interval::universe, rec1))
+            return false;
+
+        if (!boundary->hit(r, interval(rec1.t+0.0001, infinity), rec2))
+            return false;
+
+        if (debugging) std::cerr << "\nt_min=" << rec1.t << ", t_max=" << rec2.t << '\n';
+
+        if (rec1.t < ray_t.min) rec1.t = ray_t.min;
+        if (rec2.t > ray_t.max) rec2.t = ray_t.max;
+
+        if (rec1.t >= rec2.t)
+            return false;
+
+        if (rec1.t < 0)
+            rec1.t = 0;
+
+        const auto ray_length = r.direction().length();
+        const auto distance_inside_boundary = (rec2.t - rec1.t) * ray_length;
+        const auto hit_distance = neg_inv_density * log(random_double());
+
+        if (hit_distance > distance_inside_boundary)
+            return false;
+
+        rec.t = rec1.t + hit_distance / ray_length;
+        rec.p = r.at(rec.t);
+
+        if (debugging) {
+            std::cerr << "hit_distance = " <<  hit_distance << '\n'
+                      << "rec.t = " <<  rec.t << '\n'
+                      << "rec.p = " <<  rec.p << '\n';
+        }
+
+        rec.normal = vec3(1,0,0);  // arbitrary
+        rec.front_face = true;     // also arbitrary
+        rec.mat = phase_function;
+
+        return true;
+    }
+
+    aabb bounding_box() const override { return boundary->bounding_box(); }
+
+  public:
+    shared_ptr<hittable> boundary;
+    double neg_inv_density;
+    shared_ptr<material> phase_function;
+};
+
+
+#endif
diff --git a/src/TheRestOfYourLife/main.cc b/src/TheRestOfYourLife/main.cc
@@ -15,6 +15,7 @@
 #include "box.h"
 #include "camera.h"
 #include "color.h"
+#include "constant_medium.h"
 #include "hittable_list.h"
 #include "material.h"
 #include "scene.h"
@@ -63,6 +64,48 @@ void cornell_box(scene& scene_desc) {
     lights.add(make_shared<sphere>(point3(190, 90, 190), 90, shared_ptr<material>()));
 }
 
+void cornell_smoke(scene& scene_desc) {
+    scene_desc.image_width       = 600;
+    scene_desc.aspect_ratio      = 1.0;
+    scene_desc.samples_per_pixel = 100;
+    scene_desc.max_depth         = 50;
+    scene_desc.background        = color(0,0,0);
+
+    scene_desc.cam.lookfrom     = point3(278, 278, -800);
+    scene_desc.cam.lookat       = point3(278, 278, 0);
+    scene_desc.cam.vup          = vec3(0, 1, 0);
+    scene_desc.cam.vfov         = 40.0;
+    scene_desc.cam.aperture     = 0.0;
+    scene_desc.cam.focus_dist   = 10.0;
+
+    hittable_list& world = scene_desc.world;
+
+    auto red   = make_shared<lambertian>(color(.65, .05, .05));
+    auto white = make_shared<lambertian>(color(.73, .73, .73));
+    auto green = make_shared<lambertian>(color(.12, .45, .15));
+    auto light = make_shared<diffuse_light>(color(15, 15, 15));
+
+    world.add(make_shared<yz_rect>(0, 555, 0, 555, 555, green));
+    world.add(make_shared<yz_rect>(0, 555, 0, 555, 0, red));
+    world.add(make_shared<flip_face>(make_shared<xz_rect>(213, 343, 227, 332, 554, light)));
+    world.add(make_shared<xz_rect>(0, 555, 0, 555, 555, white));
+    world.add(make_shared<xz_rect>(0, 555, 0, 555, 0, white));
+    world.add(make_shared<xy_rect>(0, 555, 0, 555, 555, white));
+
+    shared_ptr<hittable> box1 = make_shared<box>(point3(0,0,0), point3(165,330,165), white);
+    box1 = make_shared<rotate_y>(box1, 15);
+    box1 = make_shared<translate>(box1, vec3(265,0,295));
+
+    shared_ptr<hittable> box2 = make_shared<box>(point3(0,0,0), point3(165,165,165), white);
+    box2 = make_shared<rotate_y>(box2, -18);
+    box2 = make_shared<translate>(box2, vec3(130,0,65));
+
+    world.add(make_shared<constant_medium>(box1, 0.01, color(0,0,0)));
+    world.add(make_shared<constant_medium>(box2, 0.01, color(1,1,1)));
+
+    hittable_list& lights = scene_desc.lights;
+    lights.add(make_shared<xz_rect>(213, 343, 227, 332, 554, shared_ptr<material>()));
+}
 
 int main() {
     scene scene_desc;

diff --git a/src/TheRestOfYourLife/material.h b/src/TheRestOfYourLife/material.h
@@ -151,18 +151,17 @@ class isotropic : public material {
     isotropic(color c) : albedo(make_shared<solid_color>(c)) {}
     isotropic(shared_ptr<texture> a) : albedo(a) {}
 
-    #if 0
-    // Issue #669
-    // This method doesn't match the signature in the base `material` class, so this one's
-    // never actually called. Disabling this definition until we sort this out.
+    bool scatter(const ray& r_in, const hit_record& rec, scatter_record& srec) const override {
+        srec.attenuation = albedo->value(rec.u, rec.v, rec.p);
+        srec.pdf_ptr = make_shared<sphere_pdf>();
+        srec.skip_pdf = false;
+        return true;
+    }
 
-    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
+    double scattering_pdf(const ray& r_in, const hit_record& rec, const ray& scattered)
     const override {
-        scattered = ray(rec.p, random_in_unit_sphere(), r_in.time());
-        attenuation = albedo->value(rec.u, rec.v, rec.p);
-        return true;
+        return 1 / (4 * pi);
     }
-    #endif
 
   public:
     shared_ptr<texture> albedo;

diff --git a/src/TheRestOfYourLife/pdf.h b/src/TheRestOfYourLife/pdf.h
@@ -43,6 +43,20 @@ class cosine_pdf : public pdf {
 };
 
 
+class sphere_pdf : public pdf {
+  public:
+    sphere_pdf() { }
+
+    double value(const vec3& direction) const override {
+        return 1/ (4 * pi);
+    }
+
+    vec3 generate() const override {
+        return random_unit_vector();
+    }
+};
+
+
 class hittable_pdf : public pdf {
   public:
     hittable_pdf(const hittable_list& _objects, const point3& _origin)