ray origin() and direction() getters return const&

Update the ray::origin() and ray::direction() functions to return a
const reference to their members instead of always making a return value
copy.

Author: hollasch

books/RayTracingInOneWeekend.html

@@ -508,8 +508,8 @@
 
         ray(const point3& origin, const vec3& direction) : orig(origin), dir(direction) {}
 
-        point3 origin() const  { return orig; }
-        vec3 direction() const { return dir; }
+        const point3& origin() const  { return orig; }
+        const vec3& direction() const { return dir; }
 
         point3 at(double t) const {
             return orig + t*dir;
@@ -526,6 +526,10 @@
 
 </div>
 
+(For those unfamiliar with C++, the functions `ray::origin()` and `ray::direction()` both return an
+immutable reference to their members. Callers can either just use the reference directly, or make a
+mutable copy depending on their needs.)
+
 
 Sending Rays Into the Scene
 ----------------------------

books/RayTracingTheNextWeek.html

@@ -78,10 +78,12 @@
           : orig(origin), dir(direction), tm(time) {}
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
-        point3 origin() const  { return orig; }
-        vec3 direction() const { return dir; }
+        const point3& origin() const  { return orig; }
+        const vec3& direction() const { return dir; }
+
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-        double time() const    { return tm; }
+        double time() const { return tm; }
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
 
         point3 at(double t) const {

src/InOneWeekend/ray.h

@@ -20,8 +20,8 @@ class ray {
 
     ray(const point3& origin, const vec3& direction) : orig(origin), dir(direction) {}
 
-    point3 origin() const  { return orig; }
-    vec3 direction() const { return dir; }
+    const point3& origin() const  { return orig; }
+    const vec3& direction() const { return dir; }
 
     point3 at(double t) const {
         return orig + t*dir;

src/TheNextWeek/ray.h

@@ -24,9 +24,10 @@ class ray {
     ray(const point3& origin, const vec3& direction, double time)
       : orig(origin), dir(direction), tm(time) {}
 
-    point3 origin() const  { return orig; }
-    vec3 direction() const { return dir; }
-    double time() const    { return tm; }
+    const point3& origin() const  { return orig; }
+    const vec3& direction() const { return dir; }
+
+    double time() const { return tm; }
 
     point3 at(double t) const {
         return orig + t*dir;

src/TheRestOfYourLife/ray.h

@@ -24,9 +24,10 @@ class ray {
     ray(const point3& origin, const vec3& direction, double time)
       : orig(origin), dir(direction), tm(time) {}
 
-    point3 origin() const  { return orig; }
-    vec3 direction() const { return dir; }
-    double time() const    { return tm; }
+    const point3& origin() const  { return orig; }
+    const vec3& direction() const { return dir; }
+
+    double time() const { return tm; }
 
     point3 at(double t) const {
         return orig + t*dir;