Add reverse method to QgsLineSegment2D

python/core/geometry/qgslinesegment.sip.in

@@ -175,6 +175,11 @@ If the return value is 0, then the test was unsuccessful (e.g. due to testing a
 on the line, or exactly in line with the segment) and the result is undefined.
 
 .. seealso:: :py:func:`QgsGeometryUtils.leftOfLine`
+%End
+
+    void reverse();
+%Docstring
+Reverses the line segment, so that the start and end points are flipped.
 %End
 
     bool operator==( const QgsLineSegment2D &other ) const;

src/core/geometry/qgslinesegment.h

@@ -189,6 +189,14 @@ class CORE_EXPORT QgsLineSegment2D
      */
     int pointLeftOfLine( const QgsPointXY &point ) const;
 
+    /**
+     * Reverses the line segment, so that the start and end points are flipped.
+     */
+    void reverse()
+    {
+      std::swap( mStart, mEnd );
+    }
+
     //! Equality operator
     bool operator==( const QgsLineSegment2D &other ) const
     {

tests/src/python/test_qgslinesegment.py

@@ -112,6 +112,12 @@ class TestQgsLineSegment2D(unittest.TestCase):
         self.assertEqual(segment.pointLeftOfLine(QgsPointXY(1.5, -6)), -1)
         self.assertEqual(segment.pointLeftOfLine(QgsPointXY(5, 8)), 0)
 
+    def testReverse(self):
+        segment = QgsLineSegment2D(QgsPointXY(1, 2), QgsPointXY(3, 4))
+        segment.reverse()
+        self.assertEqual(segment.start(), QgsPointXY(3, 4))
+        self.assertEqual(segment.end(), QgsPointXY(1, 2))
+
 
 if __name__ == '__main__':
     unittest.main()