1. 2D Collision Response
For CSE 3902
By: Matt Boggus

2. Collision response organization options
Response logic in client code
Methods in Mario.cs
Response logic encapsulated in dedicated classes
MarioCollisionHandler
MarioBlockHandler, MarioEnemyHandler, etc.
AllCollisionHandler

3. Separation of concerns: collision detection vs. collision response
Assume a collision detection class has already determined the type of collision (ICollision)
Left
Right
Top
Bottom
None

4. Response logic in Mario
Expect to see methods like:
void HandleBlockCollision(Block block, ICollision side)
void HandleEnemyCollision(IEnemy enemy, ICollision side)
etc.
Lowers cohesion and raises coupling of Mario class

5. Response logic in MarioCollisionHandler
Still expect to see methods like:
void HandleBlockCollision(Block block, ICollision side)
void HandleEnemyCollision(IEnemy enemy, ICollision side)
etc., assuming the class has a reference to mario stored in a field
Mario class’ cohesion and coupling remains the same as before
This class has high coupling

6. Response logic in MarioBlockCollisionHandler
Now only expect to see the method:
void HandleCollision(Mario mario, Block block, ICollision side)
This class has high cohesion and low coupling
That’s good!
Similar to the state pattern, we increase the total number of classes and risk code duplication

7. Selecting the right collision handler
Given generic storage, like
List<IGameObject> gameObjects
Decision making logic is required to determine the correct handler or methods
Can we avoid branching statements (if, else, switch)?

8. AllCollisionHandler
Consider a table of use cases

9. AllCollisionHandler
Each use case has a specific response; we can encapsulate methods using Command objects.
This makes a Dictionary that we can use for lookup.
Note: passing the data needed to carry out these commands is easier said then done.

10. Relevant design patterns for collision detection and handling
Visitor
A way of separating an algorithm (handleCollision) from an object structure on which it operates (different types of GameObjects)
Observer
The subject (the collisionHandler), maintains a list of its dependents, called observers (the GameObjects), and notifies them automatically of any state changes, usually by calling one of their methods.