Rotation of image by any arbitrary angle from its center (boostorg#565)

* basic rotation function for theta between +/- 180 deg
* added scaling matrix for same dimensions and added bound checks for theta

include/boost/gil/extension/numeric/affine.hpp

@@ -108,6 +108,66 @@ boost::gil::matrix3x2<T> inverse(boost::gil::matrix3x2<T> m)
     return res;
 }
 
+/// \fn gil::matrix3x2 center_rotate 
+/// \tparam T     Data type for source image dimensions
+/// \tparam F     Data type for angle through which image is to be rotated
+/// @param  dims  dimensions of source image
+/// @param  rads  angle through which image is to be rotated
+/// @return   A transformation matrix for rotating the source image about its center
+/// \brief    rotates an image from its center point
+///           using consecutive affine transformations.
+template<typename T, typename F> 
+boost::gil::matrix3x2<F> center_rotate(boost::gil::point<T> dims,F rads)
+{   
+    const F PI = F(3.141592653589793238);
+    const F c_theta = std::abs(std::cos(rads));
+    const F s_theta = std::abs(std::sin(rads));
+
+    // Bound checks for angle rads
+    while(rads + PI < 0) 
+    { 
+        rads = rads + PI; 
+    }
+
+    while(rads > PI)     
+    { 
+        rads = rads - PI; 
+    }
+
+    // Basic Rotation Matrix
+    boost::gil::matrix3x2<F> rotate = boost::gil::matrix3x2<F>::get_rotate(rads);
+
+    // Find distance for translating the image into view
+    boost::gil::matrix3x2<F> translation(0,0,0,0,0,0);
+    if(rads > 0) 
+    { 
+        translation.b = s_theta; 
+    }
+    else 
+    { 
+        translation.c = s_theta;
+    }
+
+    if(std::abs(rads) > PI/2) 
+    {
+        translation.a = c_theta;
+        translation.d = c_theta;
+    }
+
+    // To bring the complete image into view
+    boost::gil::matrix3x2<F> translate =
+        boost::gil::matrix3x2<F>::get_translate(-1 * dims * translation);
+
+    // To fit inside the source dimensions
+    boost::gil::matrix3x2<F> scale =
+        boost::gil::matrix3x2<F>::get_scale(
+            s_theta * dims.y / dims.x + c_theta ,
+            s_theta * dims.x / dims.y + c_theta
+        );
+
+    return scale *  translate * rotate;  
+}
+
 }} // namespace boost::gil
 
-#endif
+#endif

test/extension/numeric/matrix3x2.cpp

@@ -201,6 +201,21 @@ void test_matrix3x2_inverse()
     BOOST_TEST_WITH(p.y, p2.y, with_tolerance<double>(1e-9));
 }
 
+void test_matrix3x2_center_rotate()
+{
+    gil::point<double> dimension(100.0,100.0);
+    gil::matrix3x2<double> m1;
+
+    m1 = gil::center_rotate(dimension, HALF_PI);
+
+    BOOST_TEST_WITH(m1.a , std::cos(HALF_PI) , with_tolerance<double>(1e-9));
+    BOOST_TEST_EQ  (m1.b ,  1);
+    BOOST_TEST_EQ  (m1.c , -1);
+    BOOST_TEST_WITH(m1.d , std::cos(HALF_PI) , with_tolerance<double>(1e-9));
+    BOOST_TEST_EQ  (m1.e ,  100);
+    BOOST_TEST_WITH(m1.f , std::cos(HALF_PI) , with_tolerance<double>(1e-9));
+}
+
 int main()
 {
     test_matrix3x2_default_constructor();
@@ -215,6 +230,7 @@ int main()
     test_matrix3x2_get_translate();
     test_matrix3x2_transform();
     test_matrix3x2_inverse();
+    test_matrix3x2_center_rotate();
 
     return ::boost::report_errors();
 }