Add region::overlap to for overlapping regions

region.cpp

@@ -35,7 +35,8 @@ region<T>::region (T _x, T _y, T _w, T _h):
     y (_y),
     w (_w),
     h (_h)
-{ ; }
+{
+}
 
 
 template <typename T>
@@ -77,7 +78,7 @@ region<T>::base (void) const {
 template <typename T>
 point
 region<T>::centre (void) const {
-    double cx = x + static_cast<T>(w  / 2.0),
+    double cx = x + static_cast<T>(w / 2.0),
            cy = y + static_cast<T>(h / 2.0);
 
     return { cx, cy, 0.0 };
@@ -107,12 +108,28 @@ region<T>::contains (const point& p) const {
 template <typename T>
 bool
 region<T>::overlaps (const region<T> &rhs) const {
+    //return !overlap (rhs).empty ();
+
     return x     < rhs.x + rhs.w && 
            x + w > rhs.x &&
            y     < rhs.y + rhs.h &&
            y + h > rhs.y;
 }
 
+
+template<typename T>
+region<T>
+region<T>::overlap (const region<T> &rhs) const {
+    double newx1 = max (x, rhs.x),
+           newy1 = max (y, rhs.y),
+           newx2 = min (x + w, rhs.x + w),
+           newy2 = min (y + h, rhs.y + h);
+
+    return region<T> (newx1, newy1, newx2 - newx1, newy2 - newy1);
+    
+}
+
+
 template <typename T>
 bool
 region<T>::operator ==(const region& rhs) const

region.hpp

@@ -48,6 +48,8 @@ namespace util {
         bool contains (const point&) const; // exclusive of borders
         bool overlaps (const region<T>&) const; // exclusive of borders
 
+        region overlap (const region<T>&) const;
+
         bool operator ==(const region<T>& rhs) const;
         bool operator !=(const region<T>& rhs) const
             { return !(*this == rhs); }