Added set_aspect_ratio()

dlib/geometry/rectangle.h

@@ -602,6 +602,41 @@ namespace dlib
         return rectangle(x, y, x+rect.width()-1, y+rect.height()-1);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    inline rectangle set_aspect_ratio (
+        const rectangle& rect,
+        double ratio
+    )
+    {
+        DLIB_ASSERT(ratio > 0,
+            "\t rectangle set_aspect_ratio()"
+            << "\n\t ratio: " << ratio 
+            << "\n\t this: " << this
+            );
+
+        // aspect ratio is w/h
+
+        // we need to find the rectangle that is nearest to rect in area but
+        // with an aspect ratio of ratio.
+
+        // w/h == ratio
+        // w*h == rect.area()
+
+        if (ratio >= 1)
+        {
+            const long h = static_cast<long>(std::sqrt(rect.area()/ratio) + 0.5);
+            const long w = static_cast<long>(h*ratio + 0.5);
+            return centered_rect(rect, w, h);
+        }
+        else
+        {
+            const long w = static_cast<long>(std::sqrt(rect.area()*ratio) + 0.5);
+            const long h = static_cast<long>(w/ratio + 0.5);
+            return centered_rect(rect, w, h);
+        }
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/geometry/rectangle_abstract.h

@@ -477,6 +477,24 @@ namespace dlib
               and height)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    inline rectangle set_aspect_ratio (
+        const rectangle& rect,
+        double ratio
+    );
+    /*!
+        requires
+            - ratio > 0
+        ensures
+            - This function reshapes the given rectangle so that it has the given aspect
+              ratio.  In particular, this means we return a rectangle R such that the
+              following equations are as true as possible:
+                - R.width()/R.height() == ratio
+                - R.area() == rect.area()
+                - center(rect) == center(R)
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     inline rectangle intersect (