update method

src/doodles/doodles.py

@@ -57,6 +57,13 @@ class Doodle(ABC):
         """
         pass
 
+    def update(self) -> None:
+        """
+        An optional method, if implemented will be called every frame,
+        allowing for animation of properties.
+        """
+        pass
+
     def copy(self) -> "Doodle":
         """
         It will be useful to have the ability to obtain a copy

src/doodles/examples/balls.py

@@ -0,0 +1,44 @@
+from doodles.doodles import Group, Circle, Color
+import random
+from doodles.world import world
+
+"""
+Demonstrates two different update strategies.
+
+This uses the Template Method pattern, by implementing update
+the behavior of an object can be overriden.
+
+Sometimes a default method would be supplied, but just as often
+it is left as a pass-through like we see here.
+
+Objects without an update method are static.
+"""
+
+class Ball(Circle):
+    def __init__(self):
+        super().__init__()
+        self.speed = 0.005 + random.random() * 0.005
+
+    def update(self):
+        self.move(0, self.speed)
+        if self.y > world.HEIGHT + 20:
+            self.move(0, -world.HEIGHT-20)
+
+balls = [Ball().pos(40*i, 0).radius(10).color(Color.BLUE) for i in range(21)]
+
+
+class GravityBall(Circle):
+    def __init__(self):
+        super().__init__()
+        self.accel = 0.0000001 # accel per frame
+        self.speed = random.random() * 0.002
+
+    def update(self):
+        self.speed += self.accel
+        self.move(0, self.speed)
+        if self.y > world.HEIGHT - 10:
+            self.speed *= -0.98 # dampening
+            self.pos(self.x, world.HEIGHT - 10.01)
+
+
+grav = [GravityBall().pos(20+40*i, 0).radius(10).color(Color.PURPLE) for i in range(21)]

src/doodles/main.py

@@ -1,4 +1,5 @@
 import sys
+import time
 import copy
 import random
 import math
@@ -7,6 +8,8 @@ import importlib
 import typer
 from .world import world
 
+FPS = 60
+MS_PER_FRAME = 1000 / 60
 
 def main(modname: str):
     pygame.init()
@@ -23,13 +26,18 @@ def main(modname: str):
         except ImportError:
             raise ImportError(f"Tried to import {modname} and doodles.examples.{modname}")
 
+    elapsed = last_update = 0
+
     while True:
         for event in pygame.event.get():
             if event.type == pygame.QUIT:
                 pygame.quit()
                 sys.exit()
+        elapsed = pygame.time.get_ticks() - last_update
+        while elapsed > MS_PER_FRAME:
+            elapsed -= MS_PER_FRAME
+            world.tick()
         world.render()
-        #print(f"world contains {len(world._drawables)}")
         pygame.display.flip()
 
 

src/doodles/world.py

@@ -57,6 +57,10 @@ class World:
     def add(self, drawable):
         self._drawables.append(drawable)
 
+    def tick(self):
+        for d in self._drawables:
+            d.update()
+
     def render(self):
         """
         Draw world to screen