BUG: Fix blitting behavior in canvastools

skimage/viewer/canvastools/base.py

@@ -23,8 +23,8 @@ class CanvasToolBase(object):
             useblit = True if mpl.backends.backend.endswith('Agg') else False
         self.useblit = useblit
         if useblit:
-            bbox = self.ax.bbox
-            self.img_background = self.canvas.copy_from_bbox(bbox)
+            self.canvas.draw()
+            self.img_background = self.canvas.copy_from_bbox(self.ax.bbox)
 
     def connect_event(self, event, callback):
         """Connect callback with an event.

skimage/viewer/canvastools/line_tool.py

@@ -23,9 +23,6 @@ class LineTool(CanvasToolBase):
                  lineprops=None):
         super(LineTool, self).__init__(ax)
 
-        #TODO: Figure out how to cleanly restore image background for useblit
-        self.useblit = False
-
         props = dict(color='r', linewidth=1, alpha=0.4, solid_capstyle='butt')
         props.update(lineprops if lineprops is not None else {})
         self.linewidth = props['linewidth']
@@ -105,8 +102,9 @@ class LineTool(CanvasToolBase):
 
     def redraw(self):
         if self.useblit:
-            # self.canvas.restore_region(self.img_background)
-            self.ax.draw_artist(self._line)
+            self.canvas.restore_region(self.img_background)
+            for artist in self._artists:
+                self.ax.draw_artist(artist)
             self.canvas.blit(self.ax.bbox)
         else:
             self.canvas.draw_idle()