ENH: Add +/- key support for incrementing/decrementing the volume for 4D data sets

Add tests and update the OrthoSlicer3D docstring to describe 4D support.

Author: grlee77

nibabel/tests/test_viewers.py

@@ -15,7 +15,7 @@
 from ..viewers import OrthoSlicer3D
 
 from numpy.testing.decorators import skipif
-from numpy.testing import assert_array_equal
+from numpy.testing import assert_array_equal, assert_equal
 
 from nose.tools import assert_raises, assert_true
 
@@ -48,7 +48,17 @@ def test_viewer():
         v._on_mouse(nt('event', 'xdata ydata inaxes button')(0.5, 0.5, ax, 1))
     v._on_mouse(nt('event', 'xdata ydata inaxes button')(0.5, 0.5, None, None))
     v.set_volume_idx(1)
+
+    # decrement/increment volume numbers via keypress
     v.set_volume_idx(1)  # should just pass
+    v._on_keypress(nt('event', 'key')('-'))  # decrement
+    assert_equal(v._data_idx[3], 0)
+    v._on_keypress(nt('event', 'key')('+'))  # increment
+    assert_equal(v._data_idx[3], 1)
+    v._on_keypress(nt('event', 'key')('-'))
+    v._on_keypress(nt('event', 'key')('='))  # alternative increment key
+    assert_equal(v._data_idx[3], 1)
+
     v.close()
     v._draw()  # should be safe
 

nibabel/viewers.py

@@ -22,6 +22,12 @@ class OrthoSlicer3D(object):
     corresponding slices in the other two. Scrolling up and
     down moves the slice up and down in the current axis.
 
+    OrthoSlicer3d also supports 4-dimensional data, where multiple
+    3-dimensional volumes are stacked along the last axis.  For 4-dimensional
+    data the fourth figure axis can be used to control which 3-dimensional
+    volume is displayed.  Alternatively, the - key can be used to decrement the
+    displayed volume and the + or = keys can be used to increment it.
+
     Example
     -------
     >>> import numpy as np
@@ -436,6 +442,16 @@ def _on_keypress(self, event):
         """Handle mpl keypress events"""
         if event.key is not None and 'escape' in event.key:
             self.close()
+        elif event.key in ["=", '+']:
+            # increment volume index
+            new_idx = min(self._data_idx[3]+1, self.n_volumes)
+            self._set_volume_index(new_idx, update_slices=True)
+            self._draw()
+        elif event.key == '-':
+            # decrement volume index
+            new_idx = max(self._data_idx[3]-1, 0)
+            self._set_volume_index(new_idx, update_slices=True)
+            self._draw()
 
     def _draw(self):
         """Update all four (or three) plots"""