Add boxes to cornell box

main.cpp

@@ -251,6 +251,10 @@ void cornellBox() {
     world.add(make_shared<quad>(point3(555,555,555), vec3(-555,0,0), vec3(0,0,-555), white));
     world.add(make_shared<quad>(point3(0,0,555), vec3(555,0,0), vec3(0,555,0), white));
 
+    // Boxes. 
+    world.add(box(point3(130, 0, 65), point3(295, 165, 230), white));
+    world.add(box(point3(265, 0, 295), point3(430, 330, 460), white));
+
     camera cam;
     cam.aspectRatio = 1.0;
     cam.imageWidth = 600;

quad.h

@@ -3,6 +3,7 @@
 
 #include "rayTracer.h"
 #include "hittable.h"
+#include "hittableList.h"
 
 class quad : public hittable {
     public: 
@@ -77,5 +78,26 @@ class quad : public hittable {
         double D;
 };
 
+inline shared_ptr<hittableList> box(const point3& a, const point3& b, shared_ptr<material> mat) {
+    // Returns the 3D box (six sides) that contains the two opposite vertices a and b.
+    
+    auto sides = make_shared<hittableList>();
 
+    // Construct the two opposite vertices with the minimum and maximum coordinates. 
+    auto min = point3(fmin(a.x(), b.x()), fmin(a.y(), b.y()), fmin(a.z(), b.z()));
+    auto max = point3(fmax(a.x(), b.x()), fmax(a.y(), b.y()), fmax(a.z(), b.z()));
+
+    auto dx = vec3(max.x() - min.x(), 0, 0);
+    auto dy = vec3(0, max.y() - min.y(), 0);
+    auto dz = vec3(0, 0, max.z() - min.z());
+
+    sides->add(make_shared<quad>(point3(min.x(), min.y(), max.z()),  dx,  dy, mat)); // front
+    sides->add(make_shared<quad>(point3(max.x(), min.y(), max.z()), -dz,  dy, mat)); // right
+    sides->add(make_shared<quad>(point3(max.x(), min.y(), min.z()), -dx,  dy, mat)); // back
+    sides->add(make_shared<quad>(point3(min.x(), min.y(), min.z()),  dz,  dy, mat)); // left
+    sides->add(make_shared<quad>(point3(min.x(), max.y(), max.z()),  dx, -dz, mat)); // top
+    sides->add(make_shared<quad>(point3(min.x(), min.y(), min.z()),  dx,  dz, mat)); // bottom
+
+    return sides;
+}
 #endif