Better support for custom action handling and custom Bullet/Action subclasses.

diff --git a/bulletml/impl.py b/bulletml/impl.py
index 0548b9d1392f1c858bf71ebcc6723b1f8d22072d..e800810c798de5401b813c926a015d8e851d8919 100644 (file)
--- a/bulletml/impl.py
+++ b/bulletml/impl.py
@@ -6,15 +6,22 @@ import math
 
 from bulletml import parser
 
-# TODO(jfw): This is very non-Pythonic, it's pretty much just the
-# BulletML reference ActionImpl translated to Python.
-
 PI_2 = math.pi * 2
 
 __all__ = ["Action", "Bullet"]
 
 class Action(object):
-    """Running action implementation."""
+    """Running action implementation.
+
+    To implement new actions,
+
+    - Add a new element/class pair to parser.ActionDef.CONSTRUCTORS.
+      It should support FromXML, __getstate__, and __setstate__.
+    - Subclass impl.Action and override the 'handle' method to handle
+      your custom action type.
+    - Pass the impl.Bullet constructor your Action subclass when
+      creating your root Bullet.
+    """
 
     def __init__(self, owner, parent, actions, params, rank, repeat=1):
         self.actions = actions
@@ -61,9 +68,10 @@ class Action(object):
         self.previous_fire_direction = other.previous_fire_direction
         self.previous_fire_speed = other.previous_fire_speed
 
-    def step(self, owner, rank, created, sin=math.sin, cos=math.cos):
+    def step(self, owner, created, sin=math.sin, cos=math.cos):
         """Advance by one frame."""
         s_params = self.params
+        rank = owner.rank
 
         if self.speed_frames > 0:
             self.speed_frames -= 1
@@ -112,16 +120,17 @@ class Action(object):
 
             if isinstance(action, parser.Repeat):
                 repeat, (actions, params) = action(s_params, rank)
-                child = Action(owner, self, actions, params, rank, repeat)
+                child = self.__class__(
+                    owner, self, actions, params, rank, repeat)
                 owner.replace(self, child)
-                child.step(owner, rank, created, sin, cos)
+                child.step(owner, created, sin, cos)
                 break
 
             elif isinstance(action, (parser.ActionDef, parser.ActionRef)):
                 actions, params = action(s_params, rank)
-                child = Action(owner, self, actions, params, rank)
+                child = self.__class__(owner, self, actions, params, rank)
                 owner.replace(self, child)
-                child.step(owner, rank, created, sin, cos)
+                child.step(owner, created, sin, cos)
                 break
 
             elif isinstance(action, (parser.FireDef, parser.FireRef)):
@@ -165,7 +174,7 @@ class Action(object):
                         x += off_x
                         y += off_y
 
-                bullet = Bullet(
+                bullet = owner.__class__(
                     x, y, direction, speed, owner.target, actions, self, rank)
                 created.append(bullet)
 
@@ -251,6 +260,13 @@ class Action(object):
                 owner.vanish()
                 break
 
+            else:
+                self.handle(action, owner, created, sin, cos)
+
+    def handle(self, action, owner, created, sin, cos):
+        """Override in subclasses for new action types."""
+        raise NotImplementedError(action.__class__.__name__)
+
 class Bullet(object):
     """Simple bullet implementation.
 
@@ -274,7 +290,7 @@ class Bullet(object):
     """
 
     def __init__(self, x=0, y=0, direction=0, speed=0, target=None,
-                 actions=(), parent=None, rank=0.5):
+                 actions=(), parent=None, rank=0.5, Action=Action):
         self.x = self.px = x
         self.y = self.py = y
         self.mx = 0
@@ -352,7 +368,7 @@ class Bullet(object):
         created = []
 
         for action in self._actions:
-            action.step(self, self.rank, created, sin, cos)
+            action.step(self, created, sin, cos)
 
         self.px = self.x
         self.py = self.y