Fix failing tests. The reasons for the failures were in the following categories:

  - changes in the snapping algorithm that made the axes off by one pixel.
  - changes in text alignment.

All the text in the baseline images is non-antialiased.  This seems to be more robust to differences across freetype versions.  This involved the addition of a new rcParam 'text.antialised', used only by the Agg backend.

Additionally, some freetype-related differences still cause failures.  For those, we mark the tests as known fail if the user has a version of freethe versions that we expect to worvesions were determined using T. Robitaille's freetype differences testing tool here:

   https://github.com/astrofrog/freetype_version_testing

Fixes a bug in the SVG backend's Gouraud shading.

Force the use of the Agg backend for testing, and restore the old backend afterward.

Author: mdboom

doc/devel/coding_guide.rst

@@ -437,7 +437,7 @@ it::
   from matplotlib.testing.decorators import image_comparison
   import matplotlib.pyplot as plt
 
-  @image_comparison(baseline_images=['spines_axes_positions.png'])
+  @image_comparison(baseline_images=['spines_axes_positions'])
   def test_spines_axes_positions():
       # SF bug 2852168
       fig = plt.figure()
@@ -452,23 +452,25 @@ it::
       ax.xaxis.set_ticks_position('top')
       ax.spines['left'].set_color('none')
       ax.spines['bottom'].set_color('none')
-      fig.savefig('spines_axes_positions.png')
 
-The mechanism for comparing images is extremely simple -- it compares
-an image saved in the current directory with one from the Matplotlib
-sample_data repository. The correspondence is done by matching
-filenames, so ensure that:
+The first time this test is run, there will be no baseline image to
+compare against, so the test will fail.  Copy the output images (in
+this case `result_images/test_category/spines_axes_positions.*`) to
+the `baseline_images` tree in the source directory (in this case
+`lib/matplotlib/tests/baseline_images/test_category`) and put them
+under source code revision control (with `git add`).  When rerunning
+the tests, they should now pass.
 
- * The filename given to :meth:`~matplotlib.figure.Figure.savefig` is
-   exactly the same as the filename given to
-   :func:`~matplotlib.testing.decorators.image_comparison` in the
-   ``baseline_images`` argument.
+There are two optional keyword arguments to the `image_comparison`
+decorator:
 
- * The correct image gets added to the sample_data respository with
-   the name ``test_baseline_<IMAGE_FILENAME.png>``. (See
-   :ref:`sample-data` above for a description of how to add files to
-   the sample_data repository.)
+   - `extensions`: If you only wish to test some of the image formats
+     (rather than the default `png`, `svg` and `pdf` formats), pass a
+     list of the extensions to test.
 
+   - `tol`: This is the image matching tolerance, the default `1e-3`.
+     If some variation is expected in the image between runs, this
+     value may be adjusted.
 
 Known failing tests
 -------------------

lib/matplotlib/__init__.py

@@ -992,22 +992,28 @@ def tk_window_focus():
 
 def test(verbosity=0):
     """run the matplotlib test suite"""
-    import nose
-    import nose.plugins.builtin
-    from testing.noseclasses import KnownFailure
-    from nose.plugins.manager import PluginManager
-
-    # store the old values before overriding
-    plugins = []
-    plugins.append( KnownFailure() )
-    plugins.extend( [plugin() for plugin in nose.plugins.builtin.plugins] )
-
-    manager = PluginManager(plugins=plugins)
-    config = nose.config.Config(verbosity=verbosity, plugins=manager)
-
-    success = nose.run( defaultTest=default_test_modules,
-                        config=config,
-                        )
+    old_backend = rcParams['backend']
+    try:
+        use('agg')
+        import nose
+        import nose.plugins.builtin
+        from testing.noseclasses import KnownFailure
+        from nose.plugins.manager import PluginManager
+
+        # store the old values before overriding
+        plugins = []
+        plugins.append( KnownFailure() )
+        plugins.extend( [plugin() for plugin in nose.plugins.builtin.plugins] )
+
+        manager = PluginManager(plugins=plugins)
+        config = nose.config.Config(verbosity=verbosity, plugins=manager)
+
+        success = nose.run( defaultTest=default_test_modules,
+                            config=config,
+                            )
+    finally:
+        if old_backend.lower() != 'agg':
+            use(old_backend)
 
     return success
 

lib/matplotlib/backends/backend_agg.py

@@ -150,7 +150,7 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath):
             # We pass '0' for angle here, since it will be rotated (in raster
             # space) in the following call to draw_text_image).
             font.set_text(s, 0, flags=flags)
-        font.draw_glyphs_to_bitmap()
+        font.draw_glyphs_to_bitmap(antialiased=rcParams['text.antialiased'])
 
         #print x, y, int(x), int(y), s
 

lib/matplotlib/backends/backend_svg.py

@@ -691,13 +691,13 @@ def draw_gouraud_triangle(self, gc, points, colors, trans):
         href = '#GT%x' % self._n_gradients
         writer.element(
             'use',
-            attrib={'xlink:href': '#%s' % href,
+            attrib={'xlink:href': href,
                     'fill': rgb2hex(avg_color),
                     'fill-opacity': str(avg_color[-1])})
         for i in range(3):
             writer.element(
                 'use',
-                attrib={'xlink:href': '#%s' % href,
+                attrib={'xlink:href': href,
                         'fill': 'url(#GR%x_%d)' % (self._n_gradients, i),
                         'fill-opacity': '1',
                         'filter': 'url(#colorAdd)'})

lib/matplotlib/mathtext.py

@@ -209,7 +209,8 @@ def set_canvas_size(self, w, h, d):
 
     def render_glyph(self, ox, oy, info):
         info.font.draw_glyph_to_bitmap(
-            self.image, ox, oy - info.metrics.iceberg, info.glyph)
+            self.image, ox, oy - info.metrics.iceberg, info.glyph,
+            antialiased=rcParams['text.antialiased'])
 
     def render_rect_filled(self, x1, y1, x2, y2):
         height = max(int(y2 - y1) - 1, 0)

lib/matplotlib/rcsetup.py

@@ -406,6 +406,7 @@ def __call__(self, s):
     'text.latex.preview' : [False, validate_bool],
     'text.dvipnghack'     : [None, validate_bool_maybe_none],
     'text.hinting'        : [True, validate_bool],
+    'text.antialiased'    : [True, validate_bool],
 
     # The following are deprecated and replaced by, e.g., 'font.style'
     #'text.fontstyle'      : ['normal', str],

lib/matplotlib/testing/decorators.py

@@ -6,6 +6,7 @@
 import matplotlib.tests
 import matplotlib.units
 from matplotlib import pyplot as plt
+from matplotlib import ft2font
 import numpy as np
 from matplotlib.testing.compare import comparable_formats, compare_images
 import warnings
@@ -63,7 +64,7 @@ def teardown_class(cls):
         matplotlib.units.registry.clear()
         matplotlib.units.registry.update(cls.original_units_registry)
         warnings.resetwarnings() #reset any warning filters set in tests
-        
+
     def test(self):
         self._func()
 
@@ -77,6 +78,18 @@ def cleanup(func):
         {'_func': func})
     return new_class
 
+def check_freetype_version(ver):
+    if ver is None:
+        return True
+
+    from distutils import version
+    if isinstance(ver, str):
+        ver = (ver, ver)
+    ver = [version.StrictVersion(x) for x in ver]
+    found = version.StrictVersion(ft2font.__freetype_version__)
+
+    return found >= ver[0] and found <= ver[1]
+
 class ImageComparisonTest(CleanupTest):
     @classmethod
     def setup_class(cls):
@@ -116,18 +129,25 @@ def do_test():
 
                     err = compare_images(expected_fname, actual_fname, self._tol, in_decorator=True)
 
-                    if not os.path.exists(expected_fname):
-                        raise ImageComparisonFailure(
-                            'image does not exist: %s' % expected_fname)
-
-                    if err:
-                        raise ImageComparisonFailure(
-                            'images not close: %(actual)s vs. %(expected)s '
-                            '(RMS %(rms).3f)'%err)
+                    try:
+                        if not os.path.exists(expected_fname):
+                            raise ImageComparisonFailure(
+                                'image does not exist: %s' % expected_fname)
+
+                        if err:
+                            raise ImageComparisonFailure(
+                                'images not close: %(actual)s vs. %(expected)s '
+                                '(RMS %(rms).3f)'%err)
+                    except ImageComparisonFailure:
+                        if not check_freetype_version(self._freetype_version):
+                            raise KnownFailureTest(
+                                "Mismatched version of freetype.  Test requires '%s', you have '%s'" %
+                                (self._freetype_version, ft2font.__freetype_version__))
+                        raise
 
                 yield (do_test,)
 
-def image_comparison(baseline_images=None, extensions=None, tol=1e-3):
+def image_comparison(baseline_images=None, extensions=None, tol=1e-3, freetype_version=None):
     """
     call signature::
 
@@ -148,6 +168,13 @@ def image_comparison(baseline_images=None, extensions=None, tol=1e-3):
         If *None*, default to all supported extensions.
 
         Otherwise, a list of extensions to test. For example ['png','pdf'].
+
+      *tol*: (default 1e-3)
+        The RMS threshold above which the test is considered failed.
+
+      *freetype_version*: str or tuple
+        The expected freetype version or range of versions for this
+        test to pass.
     """
 
     if baseline_images is None:
@@ -178,7 +205,9 @@ def compare_images_decorator(func):
             {'_func': func,
              '_baseline_images': baseline_images,
              '_extensions': extensions,
-             '_tol': tol})
+             '_tol': tol,
+             '_freetype_version': freetype_version})
+
         return new_class
     return compare_images_decorator
 

lib/matplotlib/tests/__init__.py

@@ -11,3 +11,4 @@ def setup():
     rcdefaults() # Start with all defaults
     rcParams['font.family'] = 'Bitstream Vera Sans'
     rcParams['text.hinting'] = False
+    rcParams['text.antialiased'] = False