MNT: Refine error message in path chunking

herilalaina · phobson · commit 1ef4d394f007 · 2017-04-30T07:24:35.000-07:00
* Added exception handling
* Added chunksize test for backend agg
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -147,24 +147,32 @@ def draw_path(self, gc, path, transform, rgbFace=None):
         """
         nmax = rcParams['agg.path.chunksize'] # here at least for testing
         npts = path.vertices.shape[0]
+
         if (nmax > 100 and npts > nmax and path.should_simplify and
                 rgbFace is None and gc.get_hatch() is None):
-            nch = np.ceil(npts/float(nmax))
-            chsize = int(np.ceil(npts/nch))
+            nch = np.ceil(npts / float(nmax))
+            chsize = int(np.ceil(npts / nch))
             i0 = np.arange(0, npts, chsize)
             i1 = np.zeros_like(i0)
             i1[:-1] = i0[1:] - 1
             i1[-1] = npts
             for ii0, ii1 in zip(i0, i1):
-                v = path.vertices[ii0:ii1,:]
+                v = path.vertices[ii0:ii1, :]
                 c = path.codes
                 if c is not None:
                     c = c[ii0:ii1]
-                    c[0] = Path.MOVETO # move to end of last chunk
+                    c[0] = Path.MOVETO  # move to end of last chunk
                 p = Path(v, c)
-                self._renderer.draw_path(gc, p, transform, rgbFace)
+                try:
+                    self._renderer.draw_path(gc, p, transform, rgbFace)
+                except OverflowError:
+                    raise OverflowError("Exceeded cell block limit (set 'agg.path.chunksize' rcparam)")
         else:
-            self._renderer.draw_path(gc, path, transform, rgbFace)
+            try:
+                self._renderer.draw_path(gc, path, transform, rgbFace)
+            except OverflowError:
+                raise OverflowError("Exceeded cell block limit (set 'agg.path.chunksize' rcparam)")
+
 
     def draw_mathtext(self, gc, x, y, s, prop, angle):
         """
diff --git a/lib/matplotlib/tests/test_agg.py b/lib/matplotlib/tests/test_agg.py
@@ -14,7 +14,7 @@
 from matplotlib.testing.decorators import image_comparison
 from matplotlib import pyplot as plt
 from matplotlib import collections
-from matplotlib import path
+from matplotlib import path, rcParams
 from matplotlib import transforms as mtransforms
 
 
@@ -219,3 +219,18 @@ def test_too_large_image():
     buff = io.BytesIO()
     with pytest.raises(ValueError):
         fig.savefig(buff)
+
+
+def test_chunksize():
+    x = range(200)
+
+    # Test without chunksize
+    fig, ax = plt.subplots()
+    ax.plot(x, np.sin(x))
+    fig.canvas.draw()
+
+    # Test with chunksize
+    fig, ax = plt.subplots()
+    rcParams['agg.path.chunksize'] = 105
+    ax.plot(x, np.sin(x))
+    fig.canvas.draw()
