Docs: Effect managers

Author: einarf

docs/source/effectmanagers.rst

@@ -2,4 +2,68 @@
 Effect Managers
 ===============
 
-Write stuff
+An effect manager is responsible of:
+
+- Instantiating effects
+- Knowing what effect should be drawn based in some internal state
+- Reading keyboard events if this is needed (optional)
+
+This is an example of the default ``SingleEffectManager``.
+
+.. code-block:: python
+
+   class SingleEffectManager(BaseEffectManger):
+       """Run a single effect"""
+       def __init__(self, effect_module=None):
+           """
+           Initalize the manager telling it what effect should run.
+
+           :param effect_module: The effect module to run
+           """
+           self.active_effect = None
+           self.effect_module = effect_module
+
+       def pre_load(self):
+           """
+           Initialize the effect that should run.
+           """
+           # Instantiate all registered effects
+           effect_list = [cfg.cls() for name, cfg in effects.effects.items()]
+           # Find the single effect we are supposed to draw
+           for effect in effect_list:
+               if effect.name == self.effect_module:
+                   self.active_effect = effect
+
+           # Show some modest anger when we have been lied to
+           if not self.active_effect:
+               print("Cannot find effect '{}'".format(self.active_effect))
+               print("Available effects:")
+               print("\n".join(e.name for e in effect_list))
+               return False
+           return True
+
+       def post_load(self):
+           return True
+
+       def draw(self, time, frametime, target):
+           """This is called every frame by the framework"""
+           self.active_effect.draw(time, frametime, target)
+
+       def key_event(self, key, scancode, action, mods):
+           """Called on most key presses"""
+           print("SingleEffectManager:key_event", key, scancode, action, mods)
+
+It's important to understand that ``pre_load`` is called before resources are loaded
+and this is the correct place to instantiate effects. ``post_load`` is called right
+after loading is done.
+
+The ``draw`` method is called every frame and you will have to send this to the effect
+you want to draw.
+
+The ``key_events`` method will trigger on key presses.
+
+BaseEffectManger
+^^^^^^^^^^^^^^^^
+
+.. autoclass:: demosys.effects.managers.BaseEffectManger
+   :members:

docs/source/effects.rst

@@ -85,7 +85,7 @@ decides the effect should be active at least.
 
 The standard effect example:
 
-.. code-block:: bash
+.. code-block:: python
 
     from demosys.effects import effect
     from demosys.opengl import geometry