Improve development of lambertian::scatter()

Resolves #604

Author: hollasch

CHANGELOG.md

@@ -4,7 +4,8 @@ Change Log -- Ray Tracing in One Weekend
 # v3.1.2 (in progress)
 
 ### _The Rest of Your Life_
-  - Fix: missing closing parenthesis in listing 10 (#603)
+  - Fix: Missing closing parenthesis in listing 10 (#603)
+  - Fix: Tiny improvements to the lambertian::scatter() development (#604)
 
 
 ----------------------------------------------------------------------------------------------------

books/RayTracingTheRestOfYourLife.html

@@ -854,8 +854,8 @@
             virtual bool scatter(
                 const ray& r_in, const hit_record& rec, color& alb, ray& scattered, double& pdf
             ) const {
-                point3 target = rec.p + rec.normal + random_unit_vector();
-                scattered = ray(rec.p, unit_vector(target-rec.p), r_in.time());
+                auto direction = rec.normal + random_unit_vector();
+                scattered = ray(rec.p, unit_vector(direction), r_in.time());
                 alb = albedo->value(rec.u, rec.v, rec.p);
                 pdf = dot(rec.normal, scattered.direction()) / pi;
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
@@ -925,13 +925,17 @@
 randomly from the hemisphere above the surface. This would be $p(direction) = \frac{1}{2\pi}$.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    bool scatter(
+    virtual bool scatter(
         const ray& r_in, const hit_record& rec, color& alb, ray& scattered, double& pdf
     ) const {
-        vec3 direction = random_in_hemisphere(rec.normal);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        auto direction = random_in_hemisphere(rec.normal);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
         scattered = ray(rec.p, unit_vector(direction), r_in.time());
         alb = albedo->value(rec.u, rec.v, rec.p);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
         pdf = 0.5 / pi;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
         return true;
     }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1287,13 +1291,13 @@
 We can rewrite our Lambertian material using this to get:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    bool scatter(
+    virtual bool scatter(
         const ray& r_in, const hit_record& rec, color& alb, ray& scattered, double& pdf
     ) const {
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
         onb uvw;
         uvw.build_from_w(rec.normal);
-        vec3 direction = uvw.local(random_cosine_direction());
+        auto direction = uvw.local(random_cosine_direction());
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
         scattered = ray(rec.p, unit_vector(direction), r_in.time());
         alb = albedo->value(rec.u, rec.v, rec.p);
@@ -1944,7 +1948,9 @@
             lambertian(shared_ptr<texture> a) : albedo(a) {}
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-            bool scatter(const ray& r_in, const hit_record& rec, scatter_record& srec) const {
+            virtual bool scatter(
+                const ray& r_in, const hit_record& rec, scatter_record& srec
+            ) const {
                 srec.is_specular = false;
                 srec.attenuation = albedo->value(rec.u, rec.v, rec.p);
                 srec.pdf_ptr = new cosine_pdf(rec.normal);