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/src/copy.cpp

@@ -615,6 +615,28 @@ void Mat::copyTo( OutputArray _dst, InputArray _mask ) const
         copymask(ptrs[0], 0, ptrs[2], 0, ptrs[1], 0, sz, &esz);
 }
 
+/* dst = src */
+void Mat::copyAt( OutputArray _dst ) const
+{
+    CV_INSTRUMENT_REGION();
+
+    Mat dst = _dst.getMat();
+    CV_CheckTrue( !dst.empty(), "dst must not be empty" );
+    CV_CheckTypeEQ(type(), dst.type(), "Make the type of dst the same as src");
+    CV_CheckEQ(size(), dst.size(), "Make the size of dst the same as src");
+    copyTo(_dst);
+}
+void Mat::copyAt( OutputArray _dst, InputArray _mask ) const
+{
+    CV_INSTRUMENT_REGION();
+
+    Mat dst = _dst.getMat();
+    CV_CheckTrue( !dst.empty(), "dst must not be empty" );
+    CV_CheckTypeEQ(type(), dst.type(), "Make the type of dst the same as src");
+    CV_CheckEQ(size(), dst.size(), "Make the size of dst the same as src");
+    copyTo(_dst, _mask);
+}
+
 
 static bool can_apply_memset(const Mat &mat, const Scalar &s, int &fill_value)
 {