Merge pull request RayTracing#739 from RayTracing/ray-time-metal-dielectric2

hollasch · web-flow · commit 20987fb70f17 · 2020-09-30T12:22:36.000-07:00
Fix problems with material::scatter() methods
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,7 @@ Change Log -- Ray Tracing in One Weekend
 # v3.2.1 (in progress)
 
 ### Common
+  - Change: Refactored dielectric class for clarity
   - Fix: Update local Markdeep library (for offline reading) to v1.11. The prior version had
     incorrect content (#712)
 
@@ -13,13 +14,15 @@ Change Log -- Ray Tracing in One Weekend
   - Fix: Listing 29: Added missing `rtweekend.h` include (#691)
   - Fix: Undefined `vup` variable in camera definition (#686)
   - Fix: Listing 51: Add missing `hittable.h`, `rtweekend.h` includes (#693)
+  - Fix: Listing 59: ["Full glass material"] Diverged from source
   - Fix: Fix error in citation section (#721)
   - Fix: Listings 33, 39: Add  consistent function signature for `trilinear_interp` (#722)
 
 ### _The Next Week_
   - Change: `bvh_node` no longer reorders the source vector of scene objects; uses local copy
     instead (#701)
   - Delete: Remove unused u,v,w variables in initial `perlin::noise()` function (#684)
+  - Fix: Listing  5: Neglected to add ray time for metal and dielectric materials (#133)
   - Fix: Listing 15: In `bvh.h`, add missing `hittable_list.h` include (#690)
   - Fix: Listing 33, 34, 38: Change implicit casts to explicit ones (#692)
   - Fix: Listing 40: Change `perlin.h` in the caption to `texture.h` (#698)
@@ -30,10 +33,7 @@ Change Log -- Ray Tracing in One Weekend
 
 ### _The Rest of Your Life_
   - Fix: Fix errors in citation section (#721)
-
-### _The Next Week_
-  - Change: `bvh_node` no longer reorders the source vector of scene objects; uses local copy
-    instead (#701)
+  - Add: Listing 36: Add missing updates to dielectric class for updating specular in scatter record
 
 
 ----------------------------------------------------------------------------------------------------
diff --git a/books/RayTracingInOneWeekend.html b/books/RayTracingInOneWeekend.html
@@ -2395,21 +2395,22 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class dielectric : public material {
         public:
-            dielectric(double ri) : ref_idx(ri) {}
+            dielectric(double index_of_refraction) : ir(index_of_refraction) {}
 
             virtual bool scatter(
                 const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
             ) const override {
                 attenuation = color(1.0, 1.0, 1.0);
-                double etai_over_etat = rec.front_face ? (1.0 / ref_idx) : ref_idx;
+                double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
 
                 vec3 unit_direction = unit_vector(r_in.direction());
-                vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+                vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
                 scattered = ray(rec.p, refracted);
                 return true;
             }
 
-            double ref_idx;
+        public:
+            double ir; // Index of Refraction
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [dielectric]: <kbd>[material.h]</kbd> Dielectric material class that always refracts]
@@ -2458,7 +2459,7 @@
 solution does not exist, the glass cannot refract, and therefore must reflect the ray:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    if (etai_over_etat * sin_theta > 1.0) {
+    if (refraction_ratio * sin_theta > 1.0) {
         // Must Reflect
         ...
     } else {
@@ -2487,7 +2488,7 @@
     double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
     double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
 
-    if (etai_over_etat * sin_theta > 1.0) {
+    if (refraction_ratio * sin_theta > 1.0) {
         // Must Reflect
         ...
     } else {
@@ -2505,34 +2506,36 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class dielectric : public material {
         public:
-            dielectric(double ri) : ref_idx(ri) {}
+            dielectric(double index_of_refraction) : ir(index_of_refraction) {}
 
             virtual bool scatter(
                 const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
             ) const override {
                 attenuation = color(1.0, 1.0, 1.0);
-                double etai_over_etat = rec.front_face ? (1.0 / ref_idx) : ref_idx;
+                double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
 
                 vec3 unit_direction = unit_vector(r_in.direction());
-
-
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
                 double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
                 double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
-                if (etai_over_etat * sin_theta > 1.0 ) {
+
+                bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+
+                // If the ray cannot refract, then return the reflected path.
+                if (cannot_refract) {
                     vec3 reflected = reflect(unit_direction, rec.normal);
                     scattered = ray(rec.p, reflected);
                     return true;
                 }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
-                vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+                vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
                 scattered = ray(rec.p, refracted);
                 return true;
             }
 
         public:
-            double ref_idx;
+            double ir; // Index of Refraction
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [dielectric]: <kbd>[material.h]</kbd> Dielectric material class with reflection]
@@ -2580,38 +2583,37 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class dielectric : public material {
         public:
-            dielectric(double ri) : ref_idx(ri) {}
+            dielectric(double index_of_refraction) : ir(index_of_refraction) {}
 
             virtual bool scatter(
                 const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
             ) const override {
                 attenuation = color(1.0, 1.0, 1.0);
-                double etai_over_etat = rec.front_face ? (1.0 / ref_idx) : ref_idx;
+                double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
 
                 vec3 unit_direction = unit_vector(r_in.direction());
                 double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
                 double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
-                if (etai_over_etat * sin_theta > 1.0 ) {
-                    vec3 reflected = reflect(unit_direction, rec.normal);
-                    scattered = ray(rec.p, reflected);
-                    return true;
-                }
+
+                bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-                double reflect_prob = schlick(cos_theta, etai_over_etat);
-                if (random_double() < reflect_prob)
-                {
+                // If the ray cannot refract, or if it probabilistically reflects because of its
+                // grazing angle, then return the reflected path.
+                if (cannot_refract || random_double() < schlick(cos_theta, refraction_ratio)) {
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
                     vec3 reflected = reflect(unit_direction, rec.normal);
                     scattered = ray(rec.p, reflected);
                     return true;
                 }
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-                vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+
+                vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
                 scattered = ray(rec.p, refracted);
                 return true;
             }
 
         public:
-            double ref_idx;
+            double ir; // Index of Refraction
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [glass]: <kbd>[material.h]</kbd> Full glass material]
diff --git a/books/RayTracingTheNextWeek.html b/books/RayTracingTheNextWeek.html
@@ -271,13 +271,12 @@
 Tracking the Time of Ray Intersection
 --------------------------------------
 <div class='together'>
-Be sure that in the materials you have the scattered rays be at the time of the incident ray.
+Now that rays have a time property, we need to update the `material::scatter()` methods to account
+for the time of intersection:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class lambertian : public material {
-        public:
-            lambertian(const color& a) : albedo(a) {}
-
+        ...
             virtual bool scatter(
                 const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
             ) const override {
@@ -288,11 +287,51 @@
                 attenuation = albedo;
                 return true;
             }
+            ...
+    };
+
+    class metal : public material {
+        ...
+            virtual bool scatter(
+                const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
+            ) const override {
+                vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                scattered = ray(rec.p, reflected + fuzz*random_in_unit_sphere(), r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                attenuation = albedo;
+                return (dot(scattered.direction(), rec.normal) > 0);
+            }
+            ...
+    };
 
-            color albedo;
+    class dielectric : public material {
+        ...
+            virtual bool scatter(
+                const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
+            ) const override {
+
+                ...
+                if (cannot_refract || random_double() < schlick(cos_theta, refraction_ratio)) {
+                    vec3 reflected = reflect(unit_direction, rec.normal);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                    scattered = ray(rec.p, reflected, r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                    return true;
+                }
+
+                vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                scattered = ray(rec.p, refracted, r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                return true;
+            }
+            ...
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [lambertian-animate]: <kbd>[material.h]</kbd> Lambertian matrial for moving objects]
+    [Listing [material-time]: <kbd>[material.h]</kbd>
+        Handle ray time in the material::scatter() methods
+    ]
 </div>
 
 
diff --git a/books/RayTracingTheRestOfYourLife.html b/books/RayTracingTheRestOfYourLife.html
@@ -2123,7 +2123,7 @@
 <div class='together'>
 We have not yet dealt with specular surfaces, nor instances that mess with the surface normal. But
 this design is clean overall, and those are all fixable. For now, I will just fix `specular`. Metal
-is easy to fix.
+and dielectric materials are easy to fix.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class metal : public material {
@@ -2146,8 +2146,41 @@
             color albedo;
             double fuzz;
     };
+
+    ...
+
+    class dielectric : public material {
+        public:
+            ...
+            virtual bool scatter(
+                const ray& r_in, const hit_record& rec, scatter_record& srec
+            ) const override {
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                srec.is_specular = true;
+                srec.pdf_ptr = nullptr;
+                srec.attenuation = color(1.0, 1.0, 1.0);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
+
+                ...
+                if (cannot_refract || random_double() < schlick(cos_theta, refraction_ratio)) {
+                    vec3 reflected = reflect(unit_direction, rec.normal);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                    srec.specular_ray = ray(rec.p, reflected, r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                    return true;
+                }
+
+                vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+                srec.specular_ray = ray(rec.p, refracted, r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+                return true;
+            }
+        ...
+    };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [metal-scatter]: <kbd>[material.h]</kbd> The metal class scatter method]
+    [Listing [material-scatter]: <kbd>[material.h]</kbd> The metal and dielectric scatter methods]
 </div>
 
 Note that if fuzziness is high, this surface isn’t ideally specular, but the implicit sampling works
diff --git a/src/InOneWeekend/material.h b/src/InOneWeekend/material.h
@@ -71,33 +71,35 @@ class metal : public material {
 
 class dielectric : public material {
     public:
-        dielectric(double ri) : ref_idx(ri) {}
+        dielectric(double index_of_refraction) : ir(index_of_refraction) {}
 
         virtual bool scatter(
             const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
         ) const override {
             attenuation = color(1.0, 1.0, 1.0);
-            double etai_over_etat = rec.front_face ? (1.0 / ref_idx) : ref_idx;
+            double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
 
             vec3 unit_direction = unit_vector(r_in.direction());
             double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
             double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
 
-            if (  (etai_over_etat * sin_theta > 1.0)
-               || (random_double() < schlick(cos_theta, etai_over_etat))
-               ) {
+            bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+
+            // If the ray cannot refract, or if it probabilistically reflects because of its
+            // grazing angle, then return the reflected path.
+            if (cannot_refract || random_double() < schlick(cos_theta, refraction_ratio)) {
                 vec3 reflected = reflect(unit_direction, rec.normal);
                 scattered = ray(rec.p, reflected);
                 return true;
             }
 
-            vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+            vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
             scattered = ray(rec.p, refracted);
             return true;
         }
 
     public:
-        double ref_idx;
+        double ir; // Index of Refraction
 };
 
 
diff --git a/src/TheNextWeek/material.h b/src/TheNextWeek/material.h
@@ -76,33 +76,35 @@ class metal : public material {
 
 class dielectric : public material {
     public:
-        dielectric(double ri) : ref_idx(ri) {}
+        dielectric(double index_of_refraction) : ir(index_of_refraction) {}
 
         virtual bool scatter(
             const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
         ) const override {
             attenuation = color(1.0, 1.0, 1.0);
-            double etai_over_etat = (rec.front_face) ? (1.0 / ref_idx) : ref_idx;
+            double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
 
             vec3 unit_direction = unit_vector(r_in.direction());
             double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
             double sin_theta = sqrt(1.0 - cos_theta*cos_theta);
 
-            if (  (etai_over_etat * sin_theta > 1.0)
-               || (random_double() < schlick(cos_theta, etai_over_etat))
-               ) {
+            bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+
+            // If the ray cannot refract, or if it probabilistically reflects because of its
+            // grazing angle, then return the reflected path.
+            if (cannot_refract || random_double() < schlick(cos_theta, refraction_ratio)) {
                 vec3 reflected = reflect(unit_direction, rec.normal);
                 scattered = ray(rec.p, reflected, r_in.time());
                 return true;
             }
 
-            vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
+            vec3 refracted = refract(unit_direction, rec.normal, refraction_ratio);
             scattered = ray(rec.p, refracted, r_in.time());
             return true;
         }
 
     public:
-        double ref_idx;
+        double ir; // Index of Refraction
 };
 
 
diff --git a/src/TheRestOfYourLife/material.h b/src/TheRestOfYourLife/material.h
