Backport PR #20584: FIX: do not simplify path in LineCollection.get_segments

anntzer · tacaswell · commit 3adeb0006860 · 2021-07-06T18:24:19.000-04:00
Merge pull request #20584 from tacaswell/fix_linecollection_simplified_segments FIX: do not simplify path in LineCollection.get_segments Conflicts: lib/matplotlib/tests/test_collections.py - only backport the new test
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -1494,7 +1494,14 @@ 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)
 
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -868,3 +868,12 @@ def test_array_wrong_dimensions():
     pc = plt.pcolormesh(z)
     pc.set_array(z)  # 2D is OK for Quadmesh
     pc.update_scalarmappable()
+
+
+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)
