Quad bbox should consider all four vertices

Resolves #1402

Co-authored-by: Ubuntu <[email protected]>

Author: hollasch

CHANGELOG.md

@@ -22,6 +22,7 @@ then.
              yielding a 15-20% speedup (#1007)
 
 ### The Next Week
+  - Change - BBox for `quad` now considers all 4 points (#1402)
   - Change - `perlin::turb()` no longer defaults the value for the depth parameter.
   - Change - AABB automatically pads to mininmum size for any dimension; no longer requires
              primitives to call aabb::pad() function.
@@ -622,4 +623,3 @@ typesetting and source-code cleanup.
 # v1.42.0  (2018-08-26)
 
   - New - First GitHub release of _Ray Tracing: The Next Week_.
-

books/RayTracingTheNextWeek.html

@@ -1031,7 +1031,7 @@
 At this point, we're ready to use our new BVH code. Let's use it on our random spheres scene.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
-    #include "bvh.h" 
+    #include "bvh.h"
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
     ...
 
@@ -2452,7 +2452,7 @@
 are parallel) instead of a general quadrilateral. For our purposes, we'll use three geometric
 entities to define a quad:
 
-  1. $\mathbf{Q}$, the lower-left corner.
+  1. $\mathbf{Q}$, the starting corner.
   2. $\mathbf{u}$, a vector representing the first side.
      $\mathbf{Q} + \mathbf{u}$ gives one of the corners adjacent to $\mathbf{Q}$.
   3. $\mathbf{v}$, a vector representing the second side.
@@ -2547,7 +2547,10 @@
         }
 
         virtual void set_bounding_box() {
-            bbox = aabb(Q, Q + u + v);
+            // Compute the bounding box of all four vertices.
+            auto bbox_diagonal1 = aabb(Q, Q + u + v);
+            auto bbox_diagonal2 = aabb(Q + u, Q + v);
+            bbox = aabb(bbox_diagonal1, bbox_diagonal2);
         }
 
         aabb bounding_box() const override { return bbox; }
@@ -3580,7 +3583,7 @@
     const aabb aabb::empty    = aabb(interval::empty,    interval::empty,    interval::empty);
     const aabb aabb::universe = aabb(interval::universe, interval::universe, interval::universe);
 
-    
+
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++ highlight
     aabb operator+(const aabb& bbox, const vec3& offset) {
         return aabb(bbox.x + offset.x(), bbox.y + offset.y(), bbox.z + offset.z());

src/TheNextWeek/quad.h

@@ -28,7 +28,10 @@ class quad : public hittable {
     }
 
     virtual void set_bounding_box() {
-        bbox = aabb(Q, Q + u + v);
+        // Compute the bounding box of all four vertices.
+        auto bbox_diagonal1 = aabb(Q, Q + u + v);
+        auto bbox_diagonal2 = aabb(Q + u, Q + v);
+        bbox = aabb(bbox_diagonal1, bbox_diagonal2);
     }
 
     aabb bounding_box() const override { return bbox; }

src/TheRestOfYourLife/quad.h

@@ -30,7 +30,10 @@ class quad : public hittable {
     }
 
     virtual void set_bounding_box() {
-        bbox = aabb(Q, Q + u + v);
+        // Compute the bounding box of all four vertices.
+        auto bbox_diagonal1 = aabb(Q, Q + u + v);
+        auto bbox_diagonal2 = aabb(Q + u, Q + v);
+        bbox = aabb(bbox_diagonal1, bbox_diagonal2);
     }
 
     aabb bounding_box() const override { return bbox; }