Added functions to grow and shrink the border of rectangle objects.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403027

dlib/geometry/rectangle.h

@@ -395,6 +395,26 @@ namespace dlib
         return centered_rect((rect.left()+rect.right())/2,  (rect.top()+rect.bottom())/2, width, height);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    inline const rectangle shrink_rect (
+        const rectangle& rect,
+        long num 
+    )
+    {
+        return rectangle(rect.left()+num, rect.top()+num, rect.right()-num, rect.bottom()-num);
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    inline const rectangle grow_rect (
+        const rectangle& rect,
+        long num 
+    )
+    {
+        return shrink_rect(rect, -num);
+    }
+
 // ----------------------------------------------------------------------------------------
 
     inline const rectangle translate_rect (

dlib/geometry/rectangle_abstract.h

@@ -456,6 +456,30 @@ namespace dlib
               and height)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    inline const rectangle shrink_rect (
+        const rectangle& rect,
+        long num 
+    );
+    /*!
+        ensures
+            - returns rectangle(rect.left()+num, rect.top()+num, rect.right()-num, rect.bottom()-num)
+              (i.e. shrinks the given rectangle by shrinking its border by num)
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    inline const rectangle grow_rect (
+        const rectangle& rect,
+        long num 
+    );
+    /*!
+        ensures
+            - return shrink_rect(rect, -num)
+              (i.e. grows the given rectangle by expanding its border by num)
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     const rectangle translate_rect (

dlib/test/geometry.cpp

@@ -294,6 +294,37 @@ namespace
             DLIB_TEST(rot(point(0,1)) == point(-1,0));
         }
 
+        {
+            rectangle rect;
+
+            rect = grow_rect(rect,1);
+            DLIB_TEST(rect.width() == 2);
+            DLIB_TEST(rect.height() == 2);
+            DLIB_TEST(rect.left() == -1);
+            DLIB_TEST(rect.top() == -1);
+            DLIB_TEST(rect.right() == 0);
+            DLIB_TEST(rect.bottom() == 0);
+        }
+        {
+            rectangle rect;
+
+            rect = grow_rect(rect,2);
+            DLIB_TEST(rect.width() == 4);
+            DLIB_TEST(rect.height() == 4);
+            DLIB_TEST(rect.left() == -2);
+            DLIB_TEST(rect.top() == -2);
+            DLIB_TEST(rect.right() == 1);
+            DLIB_TEST(rect.bottom() == 1);
+
+            rect = shrink_rect(rect,1);
+            DLIB_TEST(rect.width() == 2);
+            DLIB_TEST(rect.height() == 2);
+            DLIB_TEST(rect.left() == -1);
+            DLIB_TEST(rect.top() == -1);
+            DLIB_TEST(rect.right() == 0);
+            DLIB_TEST(rect.bottom() == 0);
+        }
+
     }