Fix scattering_pdf implementations

Multiple implementations of the `scattering_pdf()` function in The Rest
Of Your Life returned bool, though the function is declared as returning
float. Changed all `return false` to `return 0` and verified uses.

Resolves #189

Author: Steve Hollasch

books/RayTracingTheRestOfYourLife.html

@@ -753,14 +753,17 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class material  {
         public:
+
             virtual bool scatter(const ray& r_in,
                 const hit_record& rec, vec3& albedo, ray& scattered, float& pdf) const {
                 return false;
             }
-            virtual float scattering_pdf(const ray& r_in,
-                const hit_record& rec, const ray& scattered) const {
-                return false;
+
+            virtual float scattering_pdf(const ray& r_in, const hit_record& rec,
+                                         const ray& scattered) const {
+                return 0;
             }
+
             virtual vec3 emitted(float u, float v, const vec3& p) const {
                 return vec3(0,0,0);
             }
@@ -775,13 +778,15 @@
     class lambertian : public material {
         public:
             lambertian(texture *a) : albedo(a) {}
+
             float scattering_pdf(const ray& r_in,
                 const hit_record& rec, const ray& scattered) const {
                 float cosine = dot(rec.normal, unit_vector(scattered.direction()));
                 if (cosine < 0)
                     return 0;
                 return cosine / M_PI;
             }
+
             bool scatter(const ray& r_in,
                 const hit_record& rec, vec3& alb, ray& scattered, float& pdf) const {
                 vec3 target = rec.p + rec.normal + random_in_unit_sphere();
@@ -790,6 +795,7 @@
                 pdf = dot(rec.normal, scattered.direction()) / M_PI;
                 return true;
             }
+
             texture *albedo;
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1671,9 +1677,15 @@
     class material  {
         public:
             virtual bool scatter(const ray& r_in, const hit_record& hrec,
-                scatter_record& srec) const { return false; }
+                                 scatter_record& srec) const {
+                return false;
+            }
+
             virtual float scattering_pdf(const ray& r_in, const hit_record& rec,
-                const ray& scattered) const { return false; }
+                                         const ray& scattered) const {
+                return 0;
+            }
+
             virtual vec3 emitted(const ray& r_in, const hit_record& rec,
                 float u, float v, const vec3& p) const { return vec3(0,0,0); }
     };
@@ -1686,14 +1698,18 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class lambertian : public material {
         public:
+
             lambertian(texture *a) : albedo(a) {}
+
             float scattering_pdf(const ray& r_in, const hit_record& rec,
-                const ray& scattered) const {
+                                 const ray& scattered) const {
                 float cosine = dot(rec.normal, unit_vector(scattered.direction()));
                 if (cosine < 0)
                     return 0;
                 return cosine / M_PI;
             }
+
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
             bool scatter(const ray& r_in, const hit_record& hrec,
                 scatter_record& srec) const {
@@ -1703,6 +1719,7 @@
                 return true;
             }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+
             texture *albedo;
     };
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/TheRestOfYourLife/main.cc

@@ -56,7 +56,10 @@ vec3 color(const ray& r, hittable *world, hittable *light_shape, int depth) {
                 ray scattered = ray(hrec.p, p.generate(), r.time());
                 float pdf_val = p.value(scattered.direction());
                 delete srec.pdf_ptr;
-                return emitted + srec.attenuation*hrec.mat_ptr->scattering_pdf(r, hrec, scattered)*color(scattered, world, light_shape, depth+1) / pdf_val;
+                return emitted
+                     + srec.attenuation * hrec.mat_ptr->scattering_pdf(r, hrec, scattered)
+                                        * color(scattered, world, light_shape, depth+1)
+                                        / pdf_val;
             }
         }
         else

src/TheRestOfYourLife/material.h

@@ -54,10 +54,14 @@ struct scatter_record
 class material  {
     public:
         virtual bool scatter(const ray& r_in, const hit_record& hrec, scatter_record& srec) const {
-              return false;}
+            return false;
+        }
         virtual float scattering_pdf(const ray& r_in, const hit_record& rec, const ray& scattered) const {
-              return false;}
-        virtual vec3 emitted(const ray& r_in, const hit_record& rec, float u, float v, const vec3& p) const { return vec3(0,0,0); }
+            return 0;
+        }
+        virtual vec3 emitted(const ray& r_in, const hit_record& rec, float u, float v, const vec3& p) const {
+            return vec3(0,0,0);
+        }
 };
 
 class dielectric : public material {