Added a function for computing the center of a rectangle.

dlib/geometry/rectangle.h

@@ -353,6 +353,24 @@ namespace dlib
         return result;
     }
 
+// ----------------------------------------------------------------------------------------
+
+    point center (
+        const dlib::rectangle& rect
+    )
+    {
+        point temp(rect.left() + rect.right() + 1,
+                   rect.top() + rect.bottom() + 1);
+
+        if (temp.x() < 0)
+            temp.x() -= 1;
+
+        if (temp.y() < 0)
+            temp.y() -= 1;
+
+        return temp/2;
+    }
+
 // ----------------------------------------------------------------------------------------
 
     inline long distance_to_rect_edge (

dlib/geometry/rectangle_abstract.h

@@ -402,6 +402,16 @@ namespace dlib
               The data in the input stream should be of the form [(left, top) (right, bottom)]
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    point center (
+        const dlib::rectangle& rect
+    );
+    /*!
+        ensures
+            - returns the center of the given rectangle
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     inline const rectangle centered_rect (
@@ -412,6 +422,7 @@ namespace dlib
     /*!
         ensures
             - returns a rectangle R such that:
+                - center(R) == p
                 - if (width == 0 || height == 0)
                     - R.width() == 0 
                     - R.height() == 0 
@@ -419,7 +430,6 @@ namespace dlib
                     - R.width() == width
                     - R.height() == height 
                 - R.tl_corner() == point(p.x()-width/2, p.y()-height/2)
-                - The center of R is a the point p 
     !*/
 
 // ----------------------------------------------------------------------------------------
@@ -433,6 +443,7 @@ namespace dlib
     /*!
         ensures
             - returns a rectangle R such that:
+                - center(R) == p
                 - if (width == 0 || height == 0)
                     - R.width() == 0 
                     - R.height() == 0 
@@ -440,7 +451,6 @@ namespace dlib
                     - R.width() == width
                     - R.height() == height 
                 - R.tl_corner() == point(x-width/2, y-height/2)
-                - The center of R is a the point (x,y)
     !*/
 
 // ----------------------------------------------------------------------------------------

dlib/test/geometry.cpp

@@ -349,6 +349,21 @@ namespace
 
         DLIB_TEST(rectangle() + point(5,4) + point(10,10) == rectangle(5,4,10,10));
 
+        // make sure the center of a centered rectangle is always right
+        for (long x = -10; x <= 10; ++x)
+        {
+            for (long y = -10; y <= 10; ++y)
+            {
+                for (long w = 0; w < 10; ++w)
+                {
+                    for (long h = 0; h < 10; ++h)
+                    {
+                        DLIB_TEST(center(centered_rect(x,y,w,h)) == point(x,y));
+                    }
+                }
+            }
+        }
+
     }