Remove class flip_face

With the changes made to handle surface intersection from either side
(refer to #270), we no longer have need for the `flip_face` class. This
change removes the class and the associated text in the books.

Resolves #482
Resolves #588

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -2202,82 +2202,9 @@
 <div class='together'>
 We get:
 
-  ![Image 18: Initial empty Cornell box](../images/img-2.18-cornell-initial.jpg class=pixel)
-
-</div>
-
-
-Flipped Objects
-----------------
-<div class='together'>
-This is very noisy because the light is small. But we have a problem: some of the walls are facing
-the wrong way. We haven't specified that a diffuse material should behave differently on different
-faces of the object, but what if the Cornell box had a different pattern on the inside and outside
-walls? The rectangle objects are described such that their front faces are always in the directions
-$(1,0,0)$, $(0,1,0)$, or $(0,0,1)$. We need a way to switch the faces of an object. Let’s make a
-hittable that does nothing but hold another hittable, and flips the face:
-
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    class flip_face : public hittable {
-        public:
-            flip_face(shared_ptr<hittable> p) : ptr(p) {}
-
-            virtual bool hit(const ray& r, double t_min, double t_max, hit_record& rec) const {
-                if (!ptr->hit(r, t_min, t_max, rec))
-                    return false;
-
-                rec.front_face = !rec.front_face;
-                return true;
-            }
-
-            virtual bool bounding_box(double t0, double t1, aabb& output_box) const {
-                return ptr->bounding_box(t0, t1, output_box);
-            }
-
-        public:
-            shared_ptr<hittable> ptr;
-    };
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [flip-face]: <kbd>[hittable.h]</kbd> Flip-Face function]
-</div>
-
-<div class='together'>
-This makes Cornell:
-
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    hittable_list cornell_box() {
-        hittable_list objects;
-
-        auto red   = make_shared<lambertian>(make_shared<solid_color>(.65, .05, .05));
-        auto white = make_shared<lambertian>(make_shared<solid_color>(.73, .73, .73));
-        auto green = make_shared<lambertian>(make_shared<solid_color>(.12, .45, .15));
-        auto light = make_shared<diffuse_light>(make_shared<solid_color>(15, 15, 15));
-
-
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        objects.add(make_shared<flip_face>(make_shared<yz_rect>(0, 555, 0, 555, 555, green)));
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-        objects.add(make_shared<yz_rect>(0, 555, 0, 555, 0, red));
-        objects.add(make_shared<xz_rect>(213, 343, 227, 332, 554, light));
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        objects.add(make_shared<flip_face>(make_shared<xz_rect>(0, 555, 0, 555, 555, white)));
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-        objects.add(make_shared<xz_rect>(0, 555, 0, 555, 0, white));
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        objects.add(make_shared<flip_face>(make_shared<xy_rect>(0, 555, 0, 555, 555, white)));
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-
-        return objects;
-    }
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [cornell-box-flipped]: <kbd>[main.cc]</kbd> Empty Cornell box with flipped rectangles]
-</div>
-
-<div class='together'>
-And voila:
-
-  ![Image 19: Empty Cornell box with fixed walls](../images/img-2.19-cornell-empty.jpg class=pixel)
+  ![Image 18: Empty Cornell box](../images/img-2.18-cornell-empty.jpg class=pixel)
 
+This image is very noisy because the light is small.
 </div>
 
 
@@ -2312,16 +2239,13 @@
         box_max = p1;
 
         sides.add(make_shared<xy_rect>(p0.x(), p1.x(), p0.y(), p1.y(), p1.z(), ptr));
-        sides.add(make_shared<flip_face>(
-            make_shared<xy_rect>(p0.x(), p1.x(), p0.y(), p1.y(), p0.z(), ptr)));
+        sides.add(make_shared<xy_rect>(p0.x(), p1.x(), p0.y(), p1.y(), p0.z(), ptr));
 
         sides.add(make_shared<xz_rect>(p0.x(), p1.x(), p0.z(), p1.z(), p1.y(), ptr));
-        sides.add(make_shared<flip_face>(
-            make_shared<xz_rect>(p0.x(), p1.x(), p0.z(), p1.z(), p0.y(), ptr)));
+        sides.add(make_shared<xz_rect>(p0.x(), p1.x(), p0.z(), p1.z(), p0.y(), ptr));
 
         sides.add(make_shared<yz_rect>(p0.y(), p1.y(), p0.z(), p1.z(), p1.x(), ptr));
-        sides.add(make_shared<flip_face>(
-            make_shared<yz_rect>(p0.y(), p1.y(), p0.z(), p1.z(), p0.x(), ptr)));
+        sides.add(make_shared<yz_rect>(p0.y(), p1.y(), p0.z(), p1.z(), p0.x(), ptr));
     }
 
     bool box::hit(const ray& r, double t0, double t1, hit_record& rec) const {
@@ -2344,7 +2268,7 @@
 <div class='together'>
 This gives:
 
-  ![Image 20: Cornell box with two blocks](../images/img-2.20-cornell-blocks.jpg class=pixel)
+  ![Image 19: Cornell box with two blocks](../images/img-2.19-cornell-blocks.jpg class=pixel)
 
 </div>
 
@@ -2572,7 +2496,7 @@
 <div class='together'>
 Which yields:
 
-  ![Image 21: Standard Cornell box scene](../images/img-2.21-cornell-standard.jpg class=pixel)
+  ![Image 20: Standard Cornell box scene](../images/img-2.20-cornell-standard.jpg class=pixel)
 
 </div>
 
@@ -2739,12 +2663,12 @@
         auto green = make_shared<lambertian>(make_shared<solid_color>(.12, .45, .15));
         auto light = make_shared<diffuse_light>(make_shared<solid_color>(7, 7, 7));
 
-        objects.add(make_shared<flip_face>(make_shared<yz_rect>(0, 555, 0, 555, 555, green)));
+        objects.add(make_shared<yz_rect>(0, 555, 0, 555, 555, green));
         objects.add(make_shared<yz_rect>(0, 555, 0, 555, 0, red));
         objects.add(make_shared<xz_rect>(113, 443, 127, 432, 554, light));
-        objects.add(make_shared<flip_face>(make_shared<xz_rect>(0, 555, 0, 555, 555, white)));
+        objects.add(make_shared<xz_rect>(0, 555, 0, 555, 555, white));
         objects.add(make_shared<xz_rect>(0, 555, 0, 555, 0, white));
-        objects.add(make_shared<flip_face>(make_shared<xy_rect>(0, 555, 0, 555, 555, white)));
+        objects.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);
@@ -2766,7 +2690,7 @@
 <div class='together'>
 We get:
 
-  ![Image 22: Cornell box with blocks of smoke](../images/img-2.22-cornell-smoke.jpg class=pixel)
+  ![Image 21: Cornell box with blocks of smoke](../images/img-2.21-cornell-smoke.jpg class=pixel)
 
 </div>
 
@@ -2854,7 +2778,7 @@
 <div class='together'>
 Running it with 10,000 rays per pixel yields:
 
-  ![Image 23: Final scene](../images/img-2.23-book2-final.jpg)
+  ![Image 22: Final scene](../images/img-2.22-book2-final.jpg)
 
 </div>
 

books/RayTracingTheRestOfYourLife.html

@@ -763,12 +763,12 @@
         auto green = make_shared<lambertian>(make_shared<solid_color>(.12, .45, .15));
         auto light = make_shared<diffuse_light>(make_shared<solid_color>(15, 15, 15));
 
-        world.add(make_shared<flip_face>(make_shared<yz_rect>(0, 555, 0, 555, 555, green)));
+        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<flip_face>(make_shared<xz_rect>(0, 555, 0, 555, 555, white)));
+        world.add(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<flip_face>(make_shared<xy_rect>(0, 555, 0, 555, 555, 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);
@@ -2113,12 +2113,12 @@
         auto green = make_shared<lambertian>(make_shared<solid_color>(.12, .45, .15));
         auto light = make_shared<diffuse_light>(make_shared<solid_color>(15, 15, 15));
 
-        world.add(make_shared<flip_face>(make_shared<yz_rect>(0, 555, 0, 555, 555, green)));
+        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<flip_face>(make_shared<xz_rect>(0, 555, 0, 555, 555, white)));
+        world.add(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<flip_face>(make_shared<xy_rect>(0, 555, 0, 555, 555, white)));
+        world.add(make_shared<xy_rect>(0, 555, 0, 555, 555, white));
 
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight