1. UFCEKU-20-3Web Games Programming Unity 3D Physics Colliders and Object Collisions

2. UFCEKU-20-3Web Games Programming Agenda The Unity ‘Physics Engine’ Creating and Using ‘Colliders’ Using Colliders as 'Triggers’ for Events Updating World Objects via Collision and Trigger Events

3. UFCEKU-20-3Web Games Programming The Unity Physics Engine Unity contains the powerful NVIDIA PhysX Physics Engine The physics engine provides realistic ‘motion under gravity’ characteristics when applied to objects in the 3D environment friction, acceleration, collision reactions based on the chosen physics material, metal, wood, rubber, elastic etc. The physics engine also provides basic collision detection between objects via ‘Colliders’ Objects created in Unity usually have a default collider created when the object is created – e.g. a sphere object would be created with a sphere collider. Objects imported as models would require an appropriate collider to be chosen.

4. UFCEKU-20-3Web Games Programming Collision Detection Detect when an world object or element has made contact with another world object or element Collision with world boundaries e.g. terrain Player collides with world object Player acquires a resource Collisions must be accurately detected Collision events must be handled by system logic World state changed to reflect changes made by collisions – update values, acquire energy, add time bonus, communicate with other objects via scripts etc.

5. UFCEKU-20-3Web Games Programming 2D Sprite Collisions

6. UFCEKU-20-3Web Games Programming 2D Sprite Bounding Boxes

7. UFCEKU-20-3Web Games Programming False Collisions Sprite boundaries overlap but sprites not colliding

8. UFCEKU-20-3Web Games Programming Collision Detection for 3D Some 3D scenarios may use bounding spheres A bounding sphere is a hypothetical sphere that completely encompasses an object. For finer-grain collision detection several spheres could be used on a single object Each would need to be coded to see if a collision had occurred Most 3D APIs provide some functional collision detection.

9. UFCEKU-20-3Web Games Programming Physics ‘Colliders’ in Unity 3D When choosing colliders there is a need to take account of the accuracy of collision detection required versus the computational impact of the chosen collider. A box collider would use much less computation than a mesh collider Unity also provides a capsule collider, which is the default collider for a First Person Controller.

10. UFCEKU-20-3Web Games Programming Example Colliders: Box Cube Box Collider

11. UFCEKU-20-3Web Games Programming Example Colliders: Sphere Cube Sphere Collider

12. UFCEKU-20-3Web Games Programming Example Colliders: Capsule Cube Capsule Collider

13. UFCEKU-20-3Web Games Programming Example Colliders: Mesh Cube Mesh Collider

14. UFCEKU-20-3Web Games Programming Example Colliders: False Collisions Cube Collider on Sphere False Collision

15. UFCEKU-20-3Web Games Programming Example Colliders: Imported Models Model in Maya

16. UFCEKU-20-3Web Games Programming Example Colliders: Models Box on MeshCapsule on MeshMesh on Mesh

17. UFCEKU-20-3Web Games Programming Using Colliders as ‘Colliders’ The default setting for any collider attached to an object is to restrict the object being passed through be other world objects. The collision event must be handled by a script attached to one or both of the objects involved in the collision ObjectCollisons.js Code to handle collisions

18. UFCEKU-20-3Web Games Programming Handling Events Initiated by Collisions This function is attached to the First Person Controller (Capsule Collider) function OnControllerColliderHit(hit:ControllerColliderHit){ if (hit.collider == GameObject.Find("RedSphere").collider){ Debug.Log("I've hit the Red Sphere"); }; if (hit.collider == GameObject.Find("BlueSphere").collider){ Debug.Log("I've hit the Blue Sphere"); }; Unity has a built in function for detecting collisions:

19. UFCEKU-20-3Web Games Programming Tag Names and the Tag Manager To reference objects in the collision function each object must have a name (Tag) defined via the Tag Manager The tag name used in any script reference must exactly match the tag name defined in the Tag Manager So RedSphere is not the same as redSphere

20. UFCEKU-20-3Web Games Programming Tag Manager Window RedSphere named in Tag Manager Element Slot

21. UFCEKU-20-3Web Games Programming Using Colliders as ‘Triggers’ Object collisions may be used to generate events ‘triggers’ which can be used to update logic in the World, generate actions, instantiate (create) new objects or remove unwanted objects from the world. Using triggers is one way for the player to collect items that update values via attached scripts. ObjectTriggers.js Code to handle collisions as event triggers. Objects defined as triggers can be ‘passed through’ by other objects

22. UFCEKU-20-3Web Games Programming Handling Events Initiated by Triggers This function is attached to the First Person Controller (Capsule Collider) function OnTriggerEnter(collisionInfo:Collider){ if(collisionInfo.gameObject.tag == "RedSphere"){ Debug.Log("I've gone through the Red Sphere!"); } if(collisionInfo.gameObject.tag == "BlueSphere"){ Debug.Log("I've deleted the Blue Sphere!"); Destroy(collisionInfo.gameObject); } Unity has a built in function for detecting collisions as triggers:

23. UFCEKU-20-3Web Games Programming Summary Unity has a built-in Physics Engine that provides ‘motion-under-gravity’ properties and behaviors for objects with attached physics components Basic collision detection is also provided by several default colliders such as Box and Capsule for objects created in Unity. Models with more complex mesh topology must have colliders selected to suit their purpose while considering the computational impact on system performance. Unity provides basic functions to detect and handle collision events for both collision reactions and triggers events. World objects must be named in the Tag Manager for associated scripts to reference object names accordingly. Tag names are case sensitive and must exactly match their corresponding script references.