Grease system abstract base class. Systems define behaviorial aspects of a World. All systems must define a step() method that is invoked by the world each timestep. User-defined systems are not required to subclass this class.
See an example system from the tutorial.
Bind the system to a world
Grease renderer abstract base class. Renderers define the presentation of a World. All renderers must define a draw() method that is invoked by the world when the display needs to be redrawn. User-defined renderers are not required to subclass this class.
See an example renderer from the tutorial.
Issue drawing commands for this renderer. Must be defined for all renderer classes.
Bind the system to a world