Glossary

Actors: elements that can interact with each other

• ship is an actor
• ship missiles are actors
• asteroids are actors

AnimationTime(also often called "step"): time since last update frame, usually in milliseconds

Viewport: boundary that actors can exist in

• when actor goes past viewport boundary, actor will come back through inverse viewport location
  • example:
    • viewport boundary is 600x600
    • actor exits boundary at location 0x455
    • actor will reenter viewport with same trajectory and velocity at inverse of viewport boundary exit
    • actor reenters viewport at boundary location 600x145

KeyList: list of keyCodes that will trigger events

Level: object representing the state of Actors and all other moving objects

Basic organization:

Game state is held inside Level

• Level.animate(step, keys) is a method that takes a time increment (step), the keys pressed for that step, and animates the Level actors
• CanvasDisplay displays the default stuff that doesn't have to be handled by Level (borders, background, etc)
• CanvasDisplay displays Level, including Level actors

Basic operation:

At each frame, CanvasDisplay

1. increments animationTime with time since last frame
2. clears canvas
3. draws background
4. interacts with Level:
5. passes animationTime increment to Level
6. receives new game state from Level
7. animates new game state onto canvas