quiver: handle autoscaling with quiverkey when animated

Added a test. Closes matplotlib#2616.

Author: efiring

lib/matplotlib/quiver.py

@@ -283,6 +283,8 @@ def remove(self):
 
     def _init(self):
         if True:  # not self._initialized:
+            if not self.Q._initialized:
+                self.Q._init()
             self._set_transform()
             _pivot = self.Q.pivot
             self.Q.pivot = self.pivot[self.labelpos]
@@ -485,6 +487,12 @@ def _init(self):
                 sn = max(8, min(25, math.sqrt(self.N)))
                 self.width = 0.06 * self.span / sn
 
+            # _make_verts sets self.scale if not already specified
+            if not self._initialized and self.scale is None:
+                self._make_verts(self.U, self.V)
+
+            self._initialized = True
+
     @allow_rasterization
     def draw(self, renderer):
         self._init()

lib/matplotlib/tests/baseline_images/test_quiver/quiver_animated_test_image.png

@@ -8,13 +8,13 @@
 from matplotlib.testing.decorators import image_comparison
 
 
-def draw_quiver(ax):
+def draw_quiver(ax, **kw):
     X, Y = np.meshgrid(np.arange(0, 2 * np.pi, 1),
                        np.arange(0, 2 * np.pi, 1))
     U = np.cos(X)
     V = np.sin(Y)
 
-    Q = ax.quiver(U, V)
+    Q = ax.quiver(U, V, **kw)
     return Q
 
 
@@ -45,6 +45,19 @@ def test_quiver_key_memory_leak():
     assert sys.getrefcount(qk) == 2
 
 
+@image_comparison(baseline_images=['quiver_animated_test_image'],
+                  extensions=['png'])
+def test_quiver_animate():
+    # Tests fix for #2616
+    fig, ax = plt.subplots()
+
+    Q = draw_quiver(ax, animated=True)
+
+    qk = ax.quiverkey(Q, 0.5, 0.92, 2, r'$2 \frac{m}{s}$',
+                      labelpos='W',
+                      fontproperties={'weight': 'bold'})
+
+
 @image_comparison(baseline_images=['quiver_with_key_test_image'],
                   extensions=['png'])
 def test_quiver_with_key():