Add layout manager and a circle layout

sugar/scene/CircleLayout.py

@@ -0,0 +1,21 @@
+import math
+
+from sugar.scene.LayoutManager import LayoutManager
+
+class CircleLayout(LayoutManager):
+	def __init__(self, radium):
+		LayoutManager.__init__(self)
+
+		self._radium = radium
+
+	def layout_group(self, group):
+		step = 2 * math.pi / len(group.get_actors())
+		angle = 2 * math.pi
+		for actor in group.get_actors():
+			self._update_position(actor, angle)
+			angle -= step
+
+	def _update_position(self, actor, angle):
+		x = math.cos(angle) * self._radium + self._radium
+		y = math.sin(angle) * self._radium + self._radium
+		actor.set_position(int(x), int(y))

sugar/scene/Group.py

@@ -3,12 +3,24 @@ from sugar.scene.Actor import Actor
 class Group(Actor):
 	def __init__(self):
 		self._actors = []
+		self._layout_manager = None
 
 	def add(self, actor):
 		self._actors.append(actor)
+		if self._layout_manager:
+			self._layout_manager.layout_group(slef)
 
 	def remove(self, actor):
 		self._actors.remove(actor)
+		if self._layout_manager:
+			self._layout_manager.layout_group(self)
+
+	def get_actors(self):
+		return self._actors
+
+	def set_layout_manager(self, layout_manager):
+		self._layout_manager = layout_manager
+		self._layout_manager.layout_group(self)
 
 	def render(self, drawable):
 		for actor in self._actors:

sugar/scene/LayoutManager.py

@@ -0,0 +1,7 @@
+class LayoutManager:
+	def __init__(self):
+		pass
+
+	def layout_group(self, group):
+		pass
+