Added shrink_rect() and grow_rect() for drectangle objects.

dlib/geometry/drectangle.h

@@ -365,6 +365,40 @@ namespace dlib
         return drectangle(p.x()-width/2, p.y()-height/2, p.x()+width/2, p.y()+height/2);
     }
 
+    inline const drectangle shrink_rect (
+        const drectangle& rect,
+        double num 
+    )
+    {
+        return drectangle(rect.left()+num, rect.top()+num, rect.right()-num, rect.bottom()-num);
+    }
+
+    inline const drectangle grow_rect (
+        const drectangle& rect,
+        double num 
+    )
+    {
+        return shrink_rect(rect, -num);
+    }
+
+    inline const drectangle shrink_rect (
+        const drectangle& rect,
+        double width,
+        double height
+    )
+    {
+        return drectangle(rect.left()+width, rect.top()+height, rect.right()-width, rect.bottom()-height);
+    }
+
+    inline const drectangle grow_rect (
+        const drectangle& rect,
+        double width,
+        double height
+    )
+    {
+        return shrink_rect(rect, -width, -height);
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/geometry/drectangle_abstract.h

@@ -490,6 +490,57 @@ namespace dlib
                 - R.tl_corner() == point(p.x()-width/2, p.y()-height/2)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    const drectangle shrink_rect (
+        const drectangle& rect,
+        double num 
+    );
+    /*!
+        ensures
+            - returns drectangle(rect.left()+num, rect.top()+num, rect.right()-num, rect.bottom()-num)
+              (i.e. shrinks the given drectangle by shrinking its border by num)
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    const drectangle grow_rect (
+        const drectangle& rect,
+        double num 
+    );
+    /*!
+        ensures
+            - return shrink_rect(rect, -num)
+              (i.e. grows the given drectangle by expanding its border by num)
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    const drectangle shrink_rect (
+        const drectangle& rect,
+        double width,
+        double height
+    );
+    /*!
+        ensures
+            - returns drectangle(rect.left()+width, rect.top()+height, rect.right()-width, rect.bottom()-height)
+              (i.e. shrinks the given drectangle by shrinking its left and right borders by width
+              and its top and bottom borders by height. )
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    const drectangle grow_rect (
+        const drectangle& rect,
+        double width,
+        double height
+    );
+    /*!
+        ensures
+            - return shrink_rect(rect, -width, -height)
+              (i.e. grows the given drectangle by expanding its border)
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }