Improve the efficiency as suggested by vpisarev.

Alter the Rotation enum to be unambiguous as to direction.

modules/core/include/opencv2/core.hpp

@@ -1023,9 +1023,9 @@ around both axes.
 CV_EXPORTS_W void flip(InputArray src, OutputArray dst, int flipCode);
 
 enum RotateFlags {
-    ROTATE_90 = 0, //Rotate 90 degrees clockwise
+    ROTATE_90_CLOCKWISE = 0, //Rotate 90 degrees clockwise
     ROTATE_180 = 1, //Rotate 180 degrees clockwise
-    ROTATE_270 = 2, //Rotate 270 degrees clockwise
+    ROTATE_90_COUNTERCLOCKWISE = 2, //Rotate 270 degrees clockwise
 };
 /** @brief Rotates a 2D array in multiples of 90 degrees.
 The function rotate rotates the array in one of three different ways:

modules/core/src/copy.cpp

@@ -832,14 +832,16 @@ static bool ocl_rotate(InputArray _src, OutputArray _dst, int rotateMode)
 {
     switch (rotateMode)
     {
-    case ROTATE_90:
-        flip(_src.getUMat().t(), _dst, 1);
+    case ROTATE_90_CLOCKWISE:
+        _dst.getUMat() = _src.getUMat().t();
+        flip(_dst, _dst, 1);
         break;
     case ROTATE_180:
         flip(_src, _dst, -1);
         break;
-    case ROTATE_270:
-        flip(_src.getUMat().t(), _dst, 0);
+    case ROTATE_90_COUNTERCLOCKWISE:
+        _dst.getUMat() = _src.getUMat().t();
+        flip(_dst, _dst, 0);
         break;
     default:
         break;
@@ -856,14 +858,16 @@ void rotate(InputArray _src, OutputArray _dst, int rotateMode)
 
     switch (rotateMode)
     {
-    case ROTATE_90:
-        flip(_src.getMat().t(), _dst, 1);
+    case ROTATE_90_CLOCKWISE:
+        _dst.getMat() = _src.getMat().t();
+        flip(_dst, _dst, 1);
         break;
     case ROTATE_180:
         flip(_src, _dst, -1);
         break;
-    case ROTATE_270:
-        flip(_src.getMat().t(), _dst, 0);
+    case ROTATE_90_COUNTERCLOCKWISE:
+        _dst.getMat() = _src.getMat().t();
+        flip(_dst, _dst, 0);
         break;
     default:
         break;