Added the point_rotator object.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402981

dlib/geometry/vector.h

@@ -1244,23 +1244,46 @@ namespace dlib
 
     typedef vector<long,2> point;
 
+// ----------------------------------------------------------------------------------------
+
+    class point_rotator
+    {
+    public:
+        point_rotator (
+            const double& angle
+        )
+        {
+            sin_angle = std::sin(angle);
+            cos_angle = std::cos(angle);
+        }
+
+        template <typename T>
+        const dlib::vector<T,2> operator() (
+            const dlib::vector<T,2>& p
+        ) const
+        {
+            double x = cos_angle*p.x() - sin_angle*p.y();
+            double y = sin_angle*p.x() + cos_angle*p.y();
+
+            return dlib::vector<double,2>(x,y);
+        }
+
+    private:
+        double sin_angle;
+        double cos_angle;
+    };
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>
     const dlib::vector<T,2> rotate_point (
         const dlib::vector<T,2>& center,
-        dlib::vector<T,2> p,
+        const dlib::vector<T,2>& p,
         double angle
     )
     {
-        p -= center;
-        dlib::vector<double,2> temp;
-        const double cos_angle = cos(angle);
-        const double sin_angle = sin(angle);
-        temp.x() = cos_angle*p.x() - sin_angle*p.y();
-        temp.y() = sin_angle*p.x() + cos_angle*p.y();
-
-        return temp + center;
+        point_rotator rot(angle);
+        return rot(p-center)+center;
     }
 
 // ----------------------------------------------------------------------------------------

dlib/geometry/vector_abstract.h

@@ -431,6 +431,39 @@ namespace dlib
 
     typedef vector<long,2> point;
 
+// ----------------------------------------------------------------------------------------
+
+    class point_rotator
+    {
+        /*!
+            WHAT THIS OBJECT REPRESENTS
+                This is an object that takes 2D points or vectors and 
+                rotates them around the origin by a given angle.
+        !*/
+    public:
+        point_rotator (
+            const double& angle
+        );
+        /*!
+            ensures
+                - When (*this)(p) is invoked it will return a point P such that:
+                    - P is the point p rotated counter-clockwise around the origin 
+                      angle radians.
+                      (Note that this is counter clockwise with respect to the normal
+                      coordinate system with positive y going up and positive x going
+                      to the right)
+        !*/
+
+        template <typename T>
+        const dlib::vector<T,2> operator() (
+            const dlib::vector<T,2>& p
+        ) const;
+        /*!
+            ensures
+                - rotates p and returns the result
+        !*/
+    };
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>

dlib/test/geometry.cpp

@@ -288,6 +288,10 @@ namespace
             DLIB_TEST(rotate_point(center, p1, -pi/4 + 10*pi) == point(8,-2));
             DLIB_TEST(rotate_point(center, p1, pi/4 - 10*pi) == point(8,8));
             DLIB_TEST(rotate_point(center, p1, -pi/4 - 10*pi) == point(8,-2));
+
+            point_rotator rot(pi/2);
+            DLIB_TEST(rot(point(1,0)) == point(0,1));
+            DLIB_TEST(rot(point(0,1)) == point(-1,0));
         }
 
     }