BUG : fix non-uniform grids in pcolorfast

Closes matplotlib#4227

lib/matplotlib/image.py

@@ -852,8 +852,8 @@ def make_image(self, magnification=1.0):
         l, b, r, t = self.axes.bbox.extents
         width = (round(r) + 0.5) - (round(l) - 0.5)
         height = (round(t) + 0.5) - (round(b) - 0.5)
-        width = width * magnification
-        height = height * magnification
+        width = int(width * magnification)
+        height = int(height * magnification)
         if self._rgbacache is None:
             A = self.to_rgba(self._A, bytes=True)
             self._rgbacache = A

lib/matplotlib/tests/test_axes.py

@@ -3565,6 +3565,18 @@ def test_move_offsetlabel():
     ax.yaxis.tick_right()
     assert_equal((1, 0.5), ax.yaxis.offsetText.get_position())
 
+
+@cleanup
+def test_pcolor_fast_non_uniform():
+    Z = np.arange(6).reshape((3, 2))
+    X = np.array([0, 1, 2, 10])
+    Y = np.array([0, 1, 2])
+
+    plt.figure()
+    ax = plt.subplot(111)
+    ax.pcolorfast(X, Y, Z.T)  # <-- fails
+
+
 if __name__ == '__main__':
     import nose
     import sys