support update functions

src/doodles/doodles.py

@@ -27,6 +27,7 @@ class Doodle(ABC):
         self._parent = parent
         self._color = parent._color if parent else Color.BLACK
         self._z_index = 0
+        self._updates = []
         # Is storing this vector in a tuple the right thing to do?
         # It might make more sense to store _x and _y, or use
         # a library's optimized 2D vector implementation.
@@ -55,12 +56,20 @@ class Doodle(ABC):
         """
         pass
 
+    def register_update(self, method, *args):
+        self._updates.append((method, args))
+
     def update(self) -> None:
         """
-        An optional method, if implemented will be called every frame,
-        allowing for animation of properties.
+        Default implementation is to support
+        update function behavior.
+
+        Can be overriden (see examples.balls)
+        to provide per-object update behavior.
         """
-        pass
+        for method, args in self._updates:
+            evaled_args = [arg() for arg in args]
+            method(*evaled_args)
 
     def copy(self) -> "Doodle":
         """

src/doodles/examples/clock.py

@@ -0,0 +1,9 @@
+import time
+from doodles import Circle, Color, Line, Group
+
+def create():
+    g = Group().pos(400, 300)
+    Circle(g).radius(300).color(Color.BLACK).z_index(1)
+    Circle(g).radius(290).color(Color.BROWN).z_index(10)
+    Circle(g).radius(20).color(Color.BLACK).z_index(50)
+    Line(g).vec(lambda: time.time() % 60 / 60 * 360, 200).z_index(100)

src/doodles/lines.py

@@ -1,8 +1,10 @@
 import math
 import random
 import pygame
+from typing import Callable
 from .doodles import Doodle
 
+
 class Line(Doodle):
     def __init__(self, parent=None):
         """
@@ -58,6 +60,14 @@ class Line(Doodle):
         """
         Alternate constructor, to create offset vector from angle & length.
         """
+        if isinstance(degrees, Callable):
+            self.register_update(
+                self.to,
+                lambda: magnitude * math.cos(math.radians(degrees())),
+                lambda: magnitude * math.sin(math.radians(degrees())),
+            )
+            return self
+
         return self.to(
             magnitude * math.cos(math.radians(degrees)),
             magnitude * math.sin(math.radians(degrees)),
@@ -89,4 +99,3 @@ class Line(Doodle):
             self.x + self._offset_vec[0],
             self.y + self._offset_vec[1],
         )
-