Merge pull request #27476 from s-trinh:LSD_drawSegments_avoid_exception_empty_vec

Check for empty vector to avoid throwing an exception in LineSegmentDetectorImpl::drawSegments()

modules/imgproc/src/lsd.cpp

@@ -1076,6 +1076,10 @@ void LineSegmentDetectorImpl::drawSegments(InputOutputArray _image, InputArray l
     }
 
     Mat _lines = lines.getMat();
+    if (_lines.empty())
+    {
+        return;
+    }
     const int N = _lines.checkVector(4);
 
     CV_Assert(_lines.depth() == CV_32F || _lines.depth() == CV_32S);

modules/imgproc/test/test_lsd.cpp

@@ -402,4 +402,18 @@ TEST_F(Imgproc_LSD_Common, compareSegmentsVec4i)
     ASSERT_EQ(result2, 11);
 }
 
+TEST_F(Imgproc_LSD_Common, drawSegmentsEmpty)
+{
+    Ptr<LineSegmentDetector> detector = createLineSegmentDetector(LSD_REFINE_STD);
+    Mat1b img = Mat1b::zeros(240, 320);
+
+    std::vector<Vec4i> lines_4i;
+    detector->detect(img, lines_4i);
+
+    Mat3b img_color = Mat3b::zeros(240, 320);
+    ASSERT_NO_THROW(
+        detector->drawSegments(img_color, lines_4i);
+    );
+}
+
 }} // namespace