Fix bug that caused images to be over-pixellated when zooming in

CHANGES.md

@@ -40,6 +40,9 @@ v0.8 (unreleased)
 * Add the ability to change the foreground and background color for viewers.
   [#988]
 
+* Fixed a bug that caused images to appear over-pixellated on the edges when
+  zooming in. [#1000]
+
 v0.7.3 (2016-05-04)
 -------------------
 

glue/tests/helpers.py

@@ -34,6 +34,10 @@ def make_skipper(module, label=None, version=None):
                                                                label='Astropy >= 0.4',
                                                                version='0.4')
 
+MATPLOTLIB_GE_14_INSTALLED, requires_matplotlib_ge_14 = make_skipper('matplotlib',
+                                                               label='Matplotlib >= 1.4',
+                                                               version='1.4')
+
 ASTRODENDRO_INSTALLED, requires_astrodendro = make_skipper('astrodendro')
 
 SCIPY_INSTALLED, requires_scipy = make_skipper('scipy',
@@ -90,4 +94,4 @@ def make_file(contents, suffix, decompress=False):
         try:
             os.unlink(fname)
         except WindowsError:  # on Windows the unlink can fail
-            pass
+            pass

glue/viewers/image/client.py

@@ -769,16 +769,28 @@ def check_update(self, *args):
         For the Matplotlib client, see if the view window has changed enough
         such that the images should be resampled
         """
+
         logging.getLogger(__name__).debug("check update")
+
+        # We need to make sure we reapply the aspect ratio manually here,
+        # because at this point, if the user has zoomed in to a region with a
+        # different aspect ratio than the original view, Matplotlib has not yet
+        # enforced computed the final limits. This is an issue if we have
+        # requested square pixels.
+        self.axes.apply_aspect()
+
         vw = _view_window(self._axes)
+
         if vw != self._view_window:
             logging.getLogger(__name__).debug("updating")
             self._update_and_redraw()
             self._view_window = vw
 
     def _update_and_redraw(self):
+
         self._update_data_plot()
         self._update_subset_plots()
+
         self._redraw()
 
     @requires_data

glue/viewers/image/qt/tests/test_regression.py

@@ -0,0 +1,38 @@
+# Miscellaneous regression tests for the image viewer
+
+import pytest
+import numpy as np
+
+from glue.core import Data
+from glue.viewers.image.qt import ImageWidget
+from glue.core.tests.util import simple_session
+from glue.tests.helpers import requires_matplotlib_ge_14
+
+
+@requires_matplotlib_ge_14
+@pytest.mark.mpl_image_compare(tolerance=1, savefig_kwargs={'dpi': 50})
+def test_resample_on_zoom():
+
+    # For images where the aspect ratio of pixels is fixed to be square, when
+    # the user zooms in, the limits of the axes are actually changed twice by
+    # matplotlib - a second time when the aspect ratio is enforced. So we need
+    # to make sure that we update the modest_image when this is the case.
+
+    session = simple_session()
+
+    np.random.seed(12345)
+
+    data = Data(x=np.random.random((2048, 2048)), label='image')
+    session.data_collection.append(data)
+
+    image = ImageWidget(session=session)
+    image.add_data(data)
+
+    image.show()
+
+    image.axes.figure.canvas.key_press_event('o')
+    image.axes.figure.canvas.button_press_event(200, 200, 1)
+    image.axes.figure.canvas.motion_notify_event(400, 210)
+    image.axes.figure.canvas.button_release_event(400, 210, 1)
+
+    return image.axes.figure