CarpetLib: Generalise "expand" function

Allow expanding bboxes by fractions of the stride.

2 files changed, 31 insertions, 0 deletions

diff --git a/Carpet/CarpetLib/src/bbox.cc b/Carpet/CarpetLib/src/bbox.cc
index e0b72f1a6..c5a429d5e 100644
--- a/Carpet/CarpetLib/src/bbox.cc
+++ b/Carpet/CarpetLib/src/bbox.cc
@@ -174,6 +174,22 @@ bbox<T,D> bbox<T,D>::expand (const vect<T,D>& lo, const vect<T,D>& hi) const {
   return bbox(lb,ub,str);
 }
 
+// Expand the bbox a little by multiples of a fraction of the stride
+template<typename T, int D>
+bbox<T,D> bbox<T,D>::expand (const vect<T,D>& lo, const vect<T,D>& hi,
+                             const vect<T,D>& denom) const
+{
+  // Allow expansion only into directions where the extent is not negative
+  // ASSERT_BBOX (all(lower()<=upper() or (lo==T(0) and hi==T(0))));
+  ASSERT_BBOX (all(shape()>=vect<T,D>(0) or (lo==T(0) and hi==T(0))));
+  ASSERT_BBOX (all(denom>vect<T,D>(0)));
+  const vect<T,D> str = stride();
+  ASSERT_BBOX (all (str%denom==vect<T,D>(0)));
+  const vect<T,D> lb = lower() - lo * str / denom;
+  const vect<T,D> ub = upper() + hi * str / denom;
+  return bbox(lb,ub,str);
+}
+
 // Find the smallest b-compatible box around *this
 template<typename T, int D>
 bbox<T,D> bbox<T,D>::expanded_for (const bbox& b) const {
diff --git a/Carpet/CarpetLib/src/bbox.hh b/Carpet/CarpetLib/src/bbox.hh
index d2dac83cc..c3c346058 100644
--- a/Carpet/CarpetLib/src/bbox.hh
+++ b/Carpet/CarpetLib/src/bbox.hh
@@ -153,6 +153,21 @@ public:
   bbox expand (const vect<vect<T,D>,2>& lohi) const
   { return expand (lohi[0], lohi[1]); }
   
+  /** Shift the bbox by multiples of the stride.  */
+  bbox shift (const vect<T,D>& v) const
+  { return expand (-v, v); }
+  
+  /** Expand (enlarge) the bbox by multiples of a fraction of the
+      stride.  */
+  bbox expand (const vect<T,D>& lo, const vect<T,D>& hi,
+               const vect<T,D>& denom) const;
+  bbox expand (const vect<vect<T,D>,2>& lohi, const vect<T,D>& denom) const
+  { return expand (lohi[0], lohi[1], denom); }
+  
+  /** Shift the bbox by multiples of a fraction of the stride.  */
+  bbox shift (const vect<T,D>& v, const vect<T,D>& denom) const
+  { return expand (-v, v, denom); }
+  
   /** Find the smallest b-compatible box around this bbox.
       ("compatible" means having the same stride.)  */
   bbox expanded_for (const bbox& b) const;