Implement smarter keypoint insertion (closes #5)

This is implemented by choosing the first and second existing keypoints that are closer to the insertion point and choosing the appropriate index such that the new keypoint is inserted correctly.

bob/ip/annotator/widgets.py

@@ -225,7 +225,7 @@ class Annotation(object):
   def _highlight_widget(self, k):
     """Highlights a given widget on the screen"""
 
-    if not self.active: return
+    if (not self.active) or (not self.point) or (k is None): return
     self._deemphasize_widgets()
     self.canvas.itemconfig(self.widget[k], fill=COLOR_ACTIVE)
 
@@ -238,7 +238,7 @@ class Annotation(object):
     annotated point.
     """
 
-    if self.active: return  #ignore
+    if self.active or (not self.point): return  #ignore
 
     self.active = True
 
@@ -289,8 +289,19 @@ class Annotation(object):
     ``(y,x)`` format
     """
 
-    return numpy.argmin(scipy.spatial.distance.cdist(self.point,
-      [unzoom_point(self.zoom, p)]))
+    if not self.point: return None
+    return self._k_closest_annotations(p, 1)[0]
+
+
+  def _k_closest_annotations(self, p, k):
+    """Returns the ``k`` closest elements to the location provided (in
+    ``(y,x)`` format)
+    """
+
+    distances = scipy.spatial.distance.cdist(self.point,
+        [unzoom_point(self.zoom, p)])[:,0]
+    if len(distances) == 1: return [0]
+    return numpy.argsort(distances)[:k]
 
 
   def insert_point(self, p):
@@ -302,7 +313,23 @@ class Annotation(object):
     # can't insert if no points are there...
     if not self.point: return
 
-    closest_point = self._closest_annotation(p)
+    # finds first and second closest points
+    closest_points = self._k_closest_annotations(p, 2)
+    closest_point = None
+    second_closest = None
+    if len(closest_points) >= 1:
+      closest_point = closest_points[0]
+    if len(closest_points) >= 2:
+      second_closest = closest_points[1]
+
+    if closest_point is None:  # no points yet, just append
+      return self.append_point(p)
+
+    if second_closest is not None:  # there are two points, choose
+      if closest_point < second_closest:
+        # the pointer is in highlighting the annotation before
+        closest_point = second_closest
+
     self.point.insert(closest_point, p)
 
     self.widget.insert(closest_point, self._make_cross(p))
@@ -417,7 +444,7 @@ class Annotation(object):
   def _remove_point(self, k):
     """Removes the active annotation"""
 
-    if not self.point:
+    if (not self.point) or (k is None):
       return
 
     self.point.pop(k)