...

workdir/ct/_node.py

@@ -32,8 +32,6 @@ def __init__(self, name: str, parent: 'Node'=None) -> None:
         self.scale = vec2(1, 1)
         # hierarchy
         self.children = {}
-        # box2d
-        self.b2_body = None             # box2d body attached to this node
 
         if parent is None:
             parent = Node._root
@@ -51,8 +49,15 @@ def get_node(self, path: str) -> 'Node':
             node = node.children[name]
         return node
 
+    def create_body(self) -> box2d.Body:
+        """create a box2d body attached to this node with RAII enabled"""
+        return self.RAII(box2d.Body(Node._b2_world, node=self))
+
     def RAII(self, obj):
-        """automatically destroy the object when this node is destroyed"""
+        """automatically destroy the object when this node is destroyed
+        
+        + `obj`: an object which contains a `destroy` method
+        """
         self._raii_objects.append(obj)
         return obj
 
@@ -131,24 +136,18 @@ def stop_all_coroutines(self):
         for i in range(len(self._coroutines)):
             self._coroutines[i] = None
 
-    # box2d step callbacks
     def on_box2d_pre_step(self):
-        if self.b2_body is None:
-            return
-        self.b2_body.position = self.position
-        self.b2_body.rotation = self.rotation
+        pass
 
     def on_box2d_post_step(self):
-        if self.b2_body is None:
-            return
-        self.position = self.b2_body.position
-        self.rotation = self.b2_body.rotation
+        pass
+
+
 
 def get_node(path: str) -> Node:
     return Node._root.get_node(path)
 
 
-
 def build_scene_tree(tree: dict, g, root: Node = None):
     root: Node = root or Node._root
     for key, child in tree.items():

workdir/ct/_tilemap.py

@@ -194,7 +194,7 @@ def bake_box2d_bodies(self, node: Node) -> list[box2d.Body]:
         transform = node.transform()
         cell_size = vec2(self.cell_size.x, self.cell_size.y)
         for path in res:
-            body = box2d.Body(Node._b2_world, node)
+            body = node.create_body()
             body.type = 0   # static
             vertices = []
             for v in path:

workdir/main.py

@@ -18,7 +18,7 @@ class Player(Node):
     def on_ready(self):
         self.tex = load_texture('assets/kenney_simple-space/ship_G.png')
         self.speed = 1
-        self.b2_body = Node._b2_world.create_body(self)
+        self.b2_body = self.create_body()
         # self.b2_body.set_circle_shape(0.5 * self.scale.x)
         self.b2_body.set_box_shape(0.5 * self.scale.x, 0.5 * self.scale.y)
         # self.b2_body.velocity = vec2(-1, 0)
@@ -56,13 +56,24 @@ class Ball(Node):
     def on_ready(self):
         self.tex = load_texture('assets/circle_64x64.png')
         self.scale = vec2(1, 1) * 0.4
-        self.b2_body = self.RAII(box2d.Body(Node._b2_world, node=self))
+        self.b2_body = self.create_body()
         self.b2_body.set_circle_shape(0.32 * self.scale.x)
         self.b2_body.velocity = vec2(1.5, 0)
 
     def on_render(self):
         draw_sprite(self.transform(), self.tex)
 
+    # box2d step callbacks
+    def on_box2d_pre_step(self):
+        self.b2_body.position = self.position
+        self.b2_body.rotation = self.rotation
+
+    def on_box2d_post_step(self):
+        self.position = self.b2_body.position
+        self.rotation = self.b2_body.rotation
+
+
+
 class Cell:
     def __init__(self, tex, tint_col: vec4):
         if tex is None: