Merge pull request matplotlib#20584 from tacaswell/fix_linecollection_simplified_segments

FIX: do not simplify path in LineCollection.get_segments

Author: anntzer

lib/matplotlib/collections.py

@@ -1461,7 +1461,14 @@ def get_segments(self):
         segments = []
 
         for path in self._paths:
-            vertices = [vertex for vertex, _ in path.iter_segments()]
+            vertices = [
+                vertex
+                for vertex, _
+                # Never simplify here, we want to get the data-space values
+                # back and there in no way to know the "right" simplification
+                # threshold so never try.
+                in path.iter_segments(simplify=False)
+            ]
             vertices = np.asarray(vertices)
             segments.append(vertices)
 

lib/matplotlib/tests/test_collections.py

@@ -1039,3 +1039,12 @@ def test_quadmesh_cursor_data():
         x, y = ax.transData.transform([-1, 101])
         event = MouseEvent('motion_notify_event', fig.canvas, x, y)
         assert qm.get_cursor_data(event) is None
+
+
+def test_get_segments():
+    segments = np.tile(np.linspace(0, 1, 256), (2, 1)).T
+    lc = LineCollection([segments])
+
+    readback, = lc.get_segments()
+    # these should comeback un-changed!
+    assert np.all(segments == readback)