Fix origin handling when interpolation is None in SVG backend. Issue matplotlib#925.

Author: mdboom

lib/matplotlib/backends/backend_svg.py

@@ -794,11 +794,17 @@ def draw_image(self, gc, x, y, im, dx=None, dy=None, transform=None):
                 attrib=attrib)
         else:
             flipped = self._make_flip_transform(transform)
+            flipped = np.array(flipped.to_values())
+            y = y+dy
+            if dy > 0.0:
+                flipped[3] *= -1.0
+                y *= -1.0
             attrib[u'transform'] = generate_transform(
-                [(u'matrix', flipped.to_values())])
+                [(u'matrix', flipped)])
             self.writer.element(
                 u'image',
-                x=unicode(x), y=unicode(y+dy), width=unicode(dx), height=unicode(-dy),
+                x=unicode(x), y=unicode(y),
+                width=unicode(dx), height=unicode(abs(dy)),
                 attrib=attrib)
 
         if url is not None:

lib/matplotlib/tests/baseline_images/test_image/no_interpolation_origin.pdf

@@ -152,6 +152,19 @@ def test_imshow():
     ax.set_xticks([])
     ax.set_yticks([])
 
+@image_comparison(baseline_images=['no_interpolation_origin'])
+def test_no_interpolation_origin():
+    fig = plt.figure()
+    ax = fig.add_subplot(211)
+    ax.imshow(np.arange(100).reshape((2, 50)), origin="lower", interpolation='none')
+    ax.set_xticks([])
+    ax.set_yticks([])
+
+    ax = fig.add_subplot(212)
+    ax.imshow(np.arange(100).reshape((2, 50)), interpolation='none')
+    ax.set_xticks([])
+    ax.set_yticks([])
+
 if __name__=='__main__':
     import nose
     nose.runmodule(argv=['-s','--with-doctest'], exit=False)