Merge pull request #27366 from chacha21:arrowedLine_clipped

Try to fix distant points to save time when ThickLine() calls FillConvexPoly() #27366

Proposal for #27365

cv::clipLine() is useful, but one should take care of a margin to preserve line caps.

### Pull Request Readiness Checklist

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- [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
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgproc/src/drawing.cpp

@@ -1646,6 +1646,18 @@ ThickLine( Mat& img, Point2l p0, Point2l p1, const void* color,
 {
     static const double INV_XY_ONE = 1./static_cast<double>(XY_ONE);
 
+    Rect_<int64> boundingRect(Point2l(0, 0), (Size2l)img.size());
+    if( (thickness > 1) && (shift == 0) && ( !boundingRect.contains(p0) || !boundingRect.contains(p1) ) )
+    {
+        const int margin = thickness;
+        const Point2l offset(margin, margin);
+        p0 += offset;
+        p1 += offset;
+        clipLine(Size2l(boundingRect.width+2*margin, boundingRect.height+2*margin), p0, p1);
+        p0 -= offset;
+        p1 -= offset;
+    }
+
     p0.x <<= XY_SHIFT - shift;
     p0.y <<= XY_SHIFT - shift;
     p1.x <<= XY_SHIFT - shift;