Fix up rtweekend.h introduction and use

We had neglected to delete inclusions and declarations from headers where they are now defined in `rtweekend.h`.

Author: hollasch

books/RayTracingInOneWeekend.html

@@ -1391,19 +1391,20 @@
 We need some math constants that we conveniently define in their own header file. For now we only
 need infinity, but we will also throw our own definition of pi in there, which we will need later.
 There is no standard portable definition of pi, so we just define our own constant for it. We'll
-throw common useful constants and future utility functions in `rtweekend.h`, our general main header
-file.
+also throw common useful constants and future utility functions in `rtweekend.h`, our general main
+header file.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     #ifndef RTWEEKEND_H
     #define RTWEEKEND_H
 
     #include <cmath>
+    #include <iostream>
     #include <limits>
     #include <memory>
 
 
-    // Usings
+    // C++ Std Usings
 
     using std::shared_ptr;
     using std::make_shared;
@@ -1429,8 +1430,56 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [rtweekend-initial]: <kbd>[rtweekend.h]</kbd> The rtweekend.h common header]
 
+All main program files will include `rtweekend.h` first, so most other header files (where the bulk
+of our code will reside) can assume that these definitions are already available. (Headers included
+inside `rtweekend.h` still need to include any of their dependencies.) We'll make some updates with
+this assumption in mind.
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    #include "vec3.h"
+
+    #include <iostream>
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [assume-rtw-color]: <kbd>[color.h]</kbd> Assume rtweekend.h in color.h]
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    #include "ray.h"
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [assume-rtw-hittable]: <kbd>[hittable.h]</kbd> Assume rtweekend.h in hittable.h]
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    #include <memory>
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    #include <vector>
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    using std::shared_ptr;
+    using std::make_shared;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [assume-rtw-hittable-list]: <kbd>[hittable_list.h]</kbd>
+        Assume rtweekend.h in hittable_list.h
+    ]
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    #include "vec3.h"
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [assume-rtw-sphere]: <kbd>[sphere.h]</kbd> Assume rtweekend.h in sphere.h]
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
+    #include <cmath>
+    #include <iostream>
+
+    using std::sqrt;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [assume-rtw-vec3]: <kbd>[vec3.h]</kbd> Assume rtweekend.h in vec3.h]
+
 <div class='together'>
-And the new main:
+And now the new main:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
     #include "rtweekend.h"
@@ -1443,7 +1492,10 @@
     #include "sphere.h"
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
     #include <iostream>
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ delete
@@ -2884,6 +2936,23 @@
 In service of this, we'll create a new vector method -- `vec3::near_zero()` -- that returns true if
 the vector is very close to zero in all dimensions.
 
+We'll need to use the C++ standard library function `std::fabs`, which returns the absolute value of
+its input. We'll add this to `rtweekend.h` since we'll use this in several future locations.
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    // C++ Std Usings
+
+
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
+    using std::fabs;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    using std::make_shared;
+    using std::shared_ptr;
+    using std::sqrt;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    [Listing [declare-fabs]: <kbd>rtweekend.h</kbd> Declaring std::fabs()
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class vec3 {
         ...

books/RayTracingTheNextWeek.html

@@ -845,7 +845,6 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     #include "hittable.h"
 
-    #include <memory>
     #include <vector>
 
     class hittable_list : public hittable {
@@ -2499,8 +2498,6 @@
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [perlin-turb]: <kbd>[perlin.h]</kbd> Turbulence function]
 
-Here `fabs()` is the absolute value function defined in `<cmath>`. Now we'll use the new Perlin
-turbulence function to update our Perlin sphere:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     class noise_texture : public texture {

src/InOneWeekend/color.h

@@ -11,10 +11,6 @@
 // along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //==============================================================================================
 
-#include "vec3.h"
-
-#include <iostream>
-
 using color = vec3;
 
 inline double linear_to_gamma(double linear_component)

src/InOneWeekend/hittable_list.h

@@ -15,7 +15,6 @@
 
 #include "hittable.h"
 
-#include <memory>
 #include <vector>
 
 

src/InOneWeekend/rtweekend.h

@@ -11,11 +11,12 @@
 
 #include <cmath>
 #include <cstdlib>
+#include <iostream>
 #include <limits>
 #include <memory>
 
 
-// Usings
+// C++ Std Usings
 
 using std::shared_ptr;
 using std::make_shared;

src/InOneWeekend/vec3.h

@@ -11,10 +11,6 @@
 // along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //==============================================================================================
 
-#include <cmath>
-#include <iostream>
-
-using std::sqrt;
 using std::fabs;
 
 class vec3 {

src/TheNextWeek/color.h

@@ -11,10 +11,6 @@
 // along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //==============================================================================================
 
-#include "vec3.h"
-
-#include <iostream>
-
 using color = vec3;
 
 inline double linear_to_gamma(double linear_component)

src/TheNextWeek/hittable_list.h

@@ -16,7 +16,6 @@
 #include "aabb.h"
 #include "hittable.h"
 
-#include <memory>
 #include <vector>
 
 

src/TheNextWeek/rtweekend.h

@@ -11,11 +11,12 @@
 
 #include <cmath>
 #include <cstdlib>
+#include <iostream>
 #include <limits>
 #include <memory>
 
 
-// Usings
+// C++ Std Usings
 
 using std::shared_ptr;
 using std::make_shared;

src/TheNextWeek/vec3.h

@@ -11,10 +11,6 @@
 // along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
 //==============================================================================================
 
-#include <cmath>
-#include <iostream>
-
-using std::sqrt;
 using std::fabs;
 
 class vec3 {