Merge pull request #27318 from Kumataro:fix27298

core: add copyAt() for ROI operation #27318

Close https://github.com/opencv/opencv/issues/27320
Close https://github.com/opencv/opencv/issues/27298

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/core/include/opencv2/core/mat.hpp

@@ -1237,8 +1237,13 @@ public:
 
     When the operation mask is specified, if the Mat::create call shown above reallocates the matrix,
     the newly allocated matrix is initialized with all zeros before copying the data.
+
+    If (re)allocation of destination memory is not necessary (e.g. updating ROI), use copyAt() .
+
     @param m Destination matrix. If it does not have a proper size or type before the operation, it is
     reallocated.
+
+    @sa copyAt
      */
     void copyTo( OutputArray m ) const;
 
@@ -1250,6 +1255,30 @@ public:
     */
     void copyTo( OutputArray m, InputArray mask ) const;
 
+    /** @brief Overwrites the existing matrix
+
+    This method writes existing matrix data, just like copyTo().
+    But if it does not have a proper size or type before the operation, an exception is thrown.
+    This function is helpful to update ROI in an existing matrix.
+
+    If (re)allocation of destination memory is necessary, use copyTo() .
+
+    @param m Destination matrix.
+    If it does not have a proper size or type before the operation, an exception is thrown.
+
+    @sa copyTo
+
+     */
+    void copyAt( OutputArray m ) const;
+
+    /** @overload
+    @param m Destination matrix.
+    If it does not have a proper size or type before the operation, an exception is thrown.
+    @param mask Operation mask of the same size as \*this. Its non-zero elements indicate which matrix
+    elements need to be copied. The mask has to be of type CV_8U and can have 1 or multiple channels.
+    */
+    void copyAt( OutputArray m, InputArray mask ) const;
+
     /** @brief Converts an array to another data type with optional scaling.
 
     The method converts source pixel values to the target data type. saturate_cast\<\> is applied at