Fix order bug with lambertian texture support

Resolves #1258

Author: hollasch

books/RayTracingTheNextWeek.html

@@ -1317,6 +1317,47 @@
 Those checker odd/even parameters can point to a constant texture or to some other procedural
 texture. This is in the spirit of shader networks introduced by Pat Hanrahan back in the 1980s.
 
+<div class='together'>
+To support procedural textures, we'll extend the `lambertian` class to work with textures instead of
+colors:
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+    #include "texture.h"
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+
+    ...
+    class lambertian : public material {
+      public:
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        lambertian(const color& a) : albedo(make_shared<solid_color>(a)) {}
+        lambertian(shared_ptr<texture> a) : albedo(a) {}
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+
+        bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
+        const override {
+            auto scatter_direction = rec.normal + random_unit_vector();
+
+            // Catch degenerate scatter direction
+            if (scatter_direction.near_zero())
+                scatter_direction = rec.normal;
+
+            scattered = ray(rec.p, scatter_direction, r_in.time());
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+            attenuation = albedo->value(rec.u, rec.v, rec.p);
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+            return true;
+        }
+
+      private:
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+        shared_ptr<texture> albedo;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    };
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [lambertian-textured]: <kbd>[material.h]</kbd> Lambertian material with texture]
+
+</div>
+
 <div class='together'>
 If we add this to our `random_scene()` function’s base sphere:
 
@@ -1346,7 +1387,7 @@
 </div>
 
 <div class='together'>
-We get:
+we get:
 
   ![<span class='num'>Image 2:</span> Spheres on checkered ground
   ](../images/img-2.02-checker-ground.png class='pixel')
@@ -1579,46 +1620,6 @@
 
 </div>
 
-<div class='together'>
-Now we can make textured materials by replacing the `const color& a` with a texture pointer:
-
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-    #include "texture.h"
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-
-    ...
-    class lambertian : public material {
-      public:
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        lambertian(const color& a) : albedo(make_shared<solid_color>(a)) {}
-        lambertian(shared_ptr<texture> a) : albedo(a) {}
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-
-        bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
-        const override {
-            auto scatter_direction = rec.normal + random_unit_vector();
-
-            // Catch degenerate scatter direction
-            if (scatter_direction.near_zero())
-                scatter_direction = rec.normal;
-
-            scattered = ray(rec.p, scatter_direction, r_in.time());
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-            attenuation = albedo->value(rec.u, rec.v, rec.p);
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-            return true;
-        }
-
-      private:
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        shared_ptr<texture> albedo;
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    };
-    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-    [Listing [lambertian-textured]: <kbd>[material.h]</kbd> Lambertian material with texture]
-
-</div>
-
 From the hitpoint $\mathbf{P}$, we compute the surface coordinates $(u,v)$. We then use these to
 index into our procedural solid texture (like marble). We can also read in an image and use the 2D
 $(u,v)$ texture coordinate to index into the image.