Fix crash when calculating offset on certain single curves which become multilinestrings when offset

nyalldawson · nyalldawson · commit 933df6684bb7 · 2018-12-08T10:21:16.000+10:00
(cherry picked from commit 34c217c) Fixes #20756
diff --git a/src/core/geometry/qgsgeometry.cpp b/src/core/geometry/qgsgeometry.cpp
@@ -1805,12 +1805,15 @@ QgsGeometry QgsGeometry::offsetCurve( double distance, int segments, JoinStyle j
       return result;
     }
 
-    const QgsCurve::Orientation newOrientation = qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->orientation();
-    if ( newOrientation != prevOrientation )
+    if ( const QgsCurve *offsetCurve = qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() ) )
     {
-      // GEOS has flipped line orientation, flip it back
-      std::unique_ptr< QgsAbstractGeometry > flipped( qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->reversed() );
-      offsetGeom = std::move( flipped );
+      const QgsCurve::Orientation newOrientation = offsetCurve->orientation();
+      if ( newOrientation != prevOrientation )
+      {
+        // GEOS has flipped line orientation, flip it back
+        std::unique_ptr< QgsAbstractGeometry > flipped( offsetCurve->reversed() );
+        offsetGeom = std::move( flipped );
+      }
     }
     return QgsGeometry( std::move( offsetGeom ) );
   }
diff --git a/tests/src/python/test_qgsgeometry.py b/tests/src/python/test_qgsgeometry.py
@@ -4601,6 +4601,8 @@ def testOffsetCurve(self):
             ["LINESTRING (0 0, 0 100, 100 100)", -1, "LineString (1 0, 1 99, 100 99)"],
             ["LINESTRING (100 100, 0 100, 0 0)", 1, "LineString (100 99, 1 99, 1 0)"],
             ["LINESTRING (100 100, 0 100, 0 0)", -1, "LineString (100 101, -1 101, -1 0)"],
+            # linestring which becomes multilinestring -- the actual offset curve calculated by GEOS looks bad, but we shouldn't crash here
+            ["LINESTRING (259329.820 5928370.79, 259324.337 5928371.758, 259319.678 5928372.33, 259317.064 5928372.498 )", 100, "MultiLineString ((259313.3 5928272.5, 259312.5 5928272.6),(259312.4 5928272.3, 259309.5 5928272.8, 259307.5 5928273.1))"],
             ["MULTILINESTRING ((0 0, 0 100, 100 100),(100 100, 0 100, 0 0))", 1, "MultiLineString ((-1 0, -1 101, 100 101),(100 99, 1 99, 1 0))"]
         ]
         for t in tests:

Original file line number	Diff line number	Diff line change
`@@ -1805,12 +1805,15 @@ QgsGeometry QgsGeometry::offsetCurve( double distance, int segments, JoinStyle j`
`1805`	`1805`	`return result;`
`1806`	`1806`	`}`
`1807`	`1807`
`1808`		`- const QgsCurve::Orientation newOrientation = qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->orientation();`
`1809`		`- if ( newOrientation != prevOrientation )`
	`1808`	`+ if ( const QgsCurve offsetCurve = qgsgeometry_cast< const QgsCurve >( offsetGeom.get() ) )`
`1810`	`1809`	`{`
`1811`		`- // GEOS has flipped line orientation, flip it back`
`1812`		`- std::unique_ptr< QgsAbstractGeometry > flipped( qgsgeometry_cast< const QgsCurve * >( offsetGeom.get() )->reversed() );`
`1813`		`- offsetGeom = std::move( flipped );`
	`1810`	`+ const QgsCurve::Orientation newOrientation = offsetCurve->orientation();`
	`1811`	`+ if ( newOrientation != prevOrientation )`
	`1812`	`+ {`
	`1813`	`+ // GEOS has flipped line orientation, flip it back`
	`1814`	`+ std::unique_ptr< QgsAbstractGeometry > flipped( offsetCurve->reversed() );`
	`1815`	`+ offsetGeom = std::move( flipped );`
	`1816`	`+ }`
`1814`	`1817`	`}`
`1815`	`1818`	`return QgsGeometry( std::move( offsetGeom ) );`
`1816`	`1819`	`}`
Original file line number	Diff line number	Diff line change
`@@ -4601,6 +4601,8 @@ def testOffsetCurve(self):`
`4601`	`4601`	`["LINESTRING (0 0, 0 100, 100 100)", -1, "LineString (1 0, 1 99, 100 99)"],`
`4602`	`4602`	`["LINESTRING (100 100, 0 100, 0 0)", 1, "LineString (100 99, 1 99, 1 0)"],`
`4603`	`4603`	`["LINESTRING (100 100, 0 100, 0 0)", -1, "LineString (100 101, -1 101, -1 0)"],`
	`4604`	`+ # linestring which becomes multilinestring -- the actual offset curve calculated by GEOS looks bad, but we shouldn't crash here`
	`4605`	`+ ["LINESTRING (259329.820 5928370.79, 259324.337 5928371.758, 259319.678 5928372.33, 259317.064 5928372.498 )", 100, "MultiLineString ((259313.3 5928272.5, 259312.5 5928272.6),(259312.4 5928272.3, 259309.5 5928272.8, 259307.5 5928273.1))"],`
`4604`	`4606`	`["MULTILINESTRING ((0 0, 0 100, 100 100),(100 100, 0 100, 0 0))", 1, "MultiLineString ((-1 0, -1 101, 100 101),(100 99, 1 99, 1 0))"]`
`4605`	`4607`	`]`
`4606`	`4608`	`for t in tests:`