Introduced update_submobject to Animation. I'd be surprised if this didn't break something.

animation/animation.py

@@ -18,6 +18,9 @@ class Animation(object):
         "name" : None,
         #Does this animation add or remove a mobject form the screen
         "remover" : False, 
+        #Options are lagged_start, smoothed_lagged_start,
+        #one_at_a_time, all_at_once
+        "submobject_mode" : "lagged_start",
     }
     def __init__(self, mobject, **kwargs):
         mobject = instantiate(mobject)
@@ -31,8 +34,6 @@ class Animation(object):
         self.update(0)
 
     def update_config(self, **kwargs):
-        if "path_arc" in kwargs:
-            kwargs["path_arc"]
         digest_config(self, kwargs)
         return self
 
@@ -49,6 +50,40 @@ class Animation(object):
             alpha = 1.0
         self.update_mobject(self.rate_func(alpha))
 
+    def update_mobject(self, alpha):
+        families = self.get_all_families_zipped()
+        for i, mobs in enumerate(families):
+            sub_alpha = self.get_sub_alpha(alpha, i, len(families))
+            self.update_submobject(*list(mobs) + [sub_alpha])
+        return self
+
+    def update_submobject(self, submobject, starting_sumobject, alpha):
+        #Typically ipmlemented by subclass
+        pass
+
+    def get_all_families_zipped(self):
+        """
+        Ordering must match the ording of arguments to update_submobject
+        """ 
+        return zip(
+            self.mobject.submobject_family(),
+            self.starting_mobject.submobject_family()
+        )
+
+    def get_sub_alpha(self, alpha, index, num_submobjects):
+        if self.submobject_mode in ["lagged_start", "smoothed_lagged_start"]:
+            prop = float(index)/num_submobjects
+            if self.submobject_mode is "smoothed_lagged_start":
+                prop = smooth(prop)
+            return np.clip(2*alpha - prop, 0, 1)
+        elif self.submobject_mode == "one_at_a_time":
+            lower = float(index)/num_submobjects
+            upper = float(index+1)/num_submobjects
+            return np.clip((alpha-lower)/(upper-lower), 0, 1)
+        elif self.submobject_mode == "all_at_once":
+            return alpha
+        raise Exception("Invalid submobject mode")
+
     def filter_out(self, *filter_functions):
         self.filter_functions += filter_functions
         return self
@@ -71,11 +106,7 @@ class Animation(object):
 
     def set_name(self, name):
         self.name = name
-        return self        
-
-    def update_mobject(self, alpha):
-        #Typically ipmlemented by subclass
-        pass
+        return self
 
     def is_remover(self):
         return self.remover