Datashade fixes (#4021)

holoviews/operation/datashader.py

@@ -27,7 +27,7 @@
     datetime_types, dt_to_int, get_param_values, max_range)
 from ..element import (Image, Path, Curve, RGB, Graph, TriMesh,
                        QuadMesh, Contours, Spikes, Area, Spread,
-                       Segments)
+                       Segments, Scatter, Points)
 from ..streams import RangeXY, PlotSize
 
 ds_version = LooseVersion(ds.__version__)
@@ -829,12 +829,12 @@ def _process(self, element, key=None):
             if isinstance(y0, datetime_types):
                 y0, y1 = dt_to_int(y0, 'ns'), dt_to_int(y1, 'ns')
             exspan, eyspan = (x1-x0), (y1-y0)
-            if np.isfinite(exspan) and exspan > 0:
-                width = min([int((xspan/exspan) * len(coords[0])), width])
+            if np.isfinite(exspan) and exspan > 0 and xspan > 0:
+                width = max([min([int((xspan/exspan) * len(coords[0])), width]), 1])
             else:
                 width = 0
-            if np.isfinite(eyspan) and eyspan > 0:
-                height = min([int((yspan/eyspan) * len(coords[1])), height])
+            if np.isfinite(eyspan) and eyspan > 0 and yspan > 0:
+                height = max([min([int((yspan/eyspan) * len(coords[1])), height]), 1])
             else:
                 height = 0
             xunit = float(xspan)/width if width else 0
@@ -847,8 +847,10 @@ def _process(self, element, key=None):
 
         params = dict(bounds=(x0, y0, x1, y1))
         if width == 0 or height == 0:
-            if width == 0: params['xdensity'] = 1
-            if height == 0: params['ydensity'] = 1
+            if width == 0:
+                params['xdensity'] = 1
+            if height == 0:
+                params['ydensity'] = 1
             return element.clone((xs, ys, np.zeros((height, width))), **params)
 
         cvs = ds.Canvas(plot_width=width, plot_height=height,
@@ -1057,17 +1059,18 @@ class rasterize(AggregationOperation):
                    (TriMesh, trimesh_rasterize),
                    (QuadMesh, quadmesh_rasterize),
                    (lambda x: (isinstance(x, NdOverlay) and
-                               issubclass(x.type, Dataset)
-                               and not issubclass(x.type, Image)),
+                               issubclass(x.type, (Scatter, Points, Curve, Path))),
                     aggregate),
                    (Spikes, spikes_aggregate),
                    (Area, area_aggregate),
                    (Spread, spread_aggregate),
                    (Segments, segments_aggregate),
                    (Contours, contours_rasterize),
-                   (lambda x: (isinstance(x, Dataset) and
-                               (not isinstance(x, Image))),
-                    aggregate)]
+                   (Graph, aggregate),
+                   (Scatter, aggregate),
+                   (Points, aggregate),
+                   (Curve, aggregate),
+                   (Path, aggregate)]
 
     def _process(self, element, key=None):
         for predicate, transform in self._transforms:

holoviews/plotting/bokeh/element.py

@@ -497,12 +497,15 @@ def _plot_properties(self, key, element):
             # Sync the plot size on dynamic plots to support accurate
             # scaling of dimension ranges
             plot_size = [s for s in self.streams if isinstance(s, PlotSize)]
+            callbacks = [c for c in self.callbacks if isinstance(c, PlotSizeCallback)]
             if plot_size:
                 stream = plot_size[0]
-                stream.add_subscriber(self._update_size)
+            elif callbacks:
+                stream = callbacks[0].streams[0]
             else:
-                stream = PlotSize(subscribers=[self._update_size])
+                stream = PlotSize()
                 self.callbacks.append(PlotSizeCallback(self, [stream], None))
+            stream.add_subscriber(self._update_size)
 
         plot_props = {
             'align':         self.align,