Implement BVH

interval.h

@@ -12,6 +12,12 @@ class interval {
 
         interval(double min, double max) : min(min), max(max) {}
 
+        interval(const interval& a, const interval& b) {
+            // Create the interval tightly enclosing the two input intervals.
+            min = a.min <= b.min ? a.min : b.min;
+            max = a.max >= b.max ? a.max : b.max;
+        }
+
         double size() const {
             return max - min;
         }
@@ -30,6 +36,11 @@ class interval {
             return x;
         }
 
+        interval expand(double delta) const {
+            auto padding = delta / 2;
+            return interval(min - padding, max + padding);
+        }
+
         static const interval empty, universe;
 };