Added the source around the shadow acne ellipse for context

Author: trevordblack

CHANGELOG.md

@@ -26,6 +26,7 @@ Change Log -- Ray Tracing in One Weekend
 
 ### In One Weekend
   - Added: More commentary about the choice between `double` and `float` (#752)
+  - Added: Software context around the shadow acne listing
 
 ### The Next Week
   - Change: Rearranged the texture-mapping presentation. The three types (solid, spatial, image) are

books/RayTracingInOneWeekend.html

@@ -1853,7 +1853,26 @@
 point approximation the sphere intersector gives us. So we need to ignore hits very near zero:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    if (world.hit(r, interval(0.001, infinity), rec)) {
+    color ray_color(const ray& r, const hittable& world, int depth) {
+        hit_record rec;
+
+
+        // If we've exceeded the ray bounce limit, no more light is gathered.
+        if (depth <= 0)
+            return color(0,0,0);
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        if (world.hit(r, interval(0.001, infinity), rec)) {
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+            point3 target = rec.p + rec.normal + random_in_unit_sphere();
+            return 0.5 * ray_color(ray(rec.p, target - rec.p), world, depth-1);
+        }
+
+        vec3 unit_direction = unit_vector(r.direction());
+        auto t = 0.5*(unit_direction.y() + 1.0);
+        return (1.0-t)*color(1.0, 1.0, 1.0) + t*color(0.5, 0.7, 1.0);
+    }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [reflect-tolerance]: <kbd>[main.cc]</kbd>
     Calculating reflected ray origins with tolerance]