These slides are part of a course about interactive objects in games. The lectures cover some of the most widely used methodologies that allow smart objects and non-player characters (NPCs) to exhibit autonomy and flexible behavior through various forms of decision making, including techniques for pathfinding, reactive behavior through automata and processes, and goal-oriented action planning. More information can be found here: http://tinyurl.com/sv-intobj-2013

1. INTERACTIVE OBJECTS IN
GAMING APPLICATIONS
Basic principles and practical scenarios in Unity
June 2013Stavros Vassos Sapienza University of Rome, DIAG, Italy vassos@dis.uniroma1.it

2. Interactive objects in games
2
 Pathfinding
 Part 1: A* heuristic search on a grid
 Part 2: Examples in Unity
 Part 3: Beyond the basics
 Action-based decision making
 AI Architectures

3. Pathfinding: Examples in Unity
3

4. Pathfinding: Examples in Unity
4
 We will use a sample project in Pathfinding.zip
 Based on
 Aron Granberg A* Pathfinding project (free version)
 http://arongranberg.com/astar/download
 http://arongranberg.com/astar/docs/getstarted.php
 3D Platformer Tutorial by Unity (free)
 http://u3d.as/content/unity-technologies/3d-platformer-
tutorial/
 Unzip, open project, and load scene “Pathfinding on
a plane” (it is already ready for experimentation)

5. Pathfinding: Examples in Unity
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 We will use a sample project in Pathfinding.zip
 Based on
 Aron Granberg A* Pathfinding project (free version)
 http://arongranberg.com/astar/download
 http://arongranberg.com/astar/docs/getstarted.php
 3D Platformer Tutorial by Unity (free)
 http://u3d.as/content/unity-technologies/3d-platformer-
tutorial/
 Unzip, open project, and load scene “Pathfinding on
a plane” (it is already ready for experimentation)
Many other packages available, paid, free, or
freemium. You can also write your own!

6. Pathfinding: Examples in Unity
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 Creating the scene
 Simple plane
 Rigid body (docs.unity3d.com:Rigidbody)
 Box collider (docs.unity3d.com:BoxCollider)
 Checkerboard material
 Crates
 Rigid body
 Box collider
 Some material that looks nice

7. Pathfinding: Examples in Unity
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 Creating the scene
 Simple plane
 Rigid body (docs.unity3d.com:Rigidbody)
 Box collider (docs.unity3d.com:BoxCollider)
 Checkerboard material
 We want to note that this is the “ground” for navigation
 Crates
 Rigid body
 Box collider
 Some material that looks nice
 We want to note that these are “obstacles” for navigation

8. Pathfinding: Examples in Unity
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 Tags: mostly for finding game objects
(docs.unity3d.com:Tags)
 Layers: mostly for rendering purposes
(docs.unity3d.com:Layers)

9. Pathfinding: Examples in Unity
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 Here we specify two layers
 Ground
 Obstacles
 And set the plane and crates to
the correct one

10. Pathfinding: Examples in Unity
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 Creating the scene
 Adding a character that we will instruct to move around
 Lerpz prefab from 3D Platformer Tutorial of Unity
 Character controller component

11. Pathfinding: Examples in Unity
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 Essentially a capsule-shaped Collider
(docs.unity3d.com:CharacterController)
 Can be told to move in some direction from a script
 Can carry out the movement but be constrained by
collisions (also step offset, slope limit)

12. Pathfinding: Examples in Unity
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 Aron’s pathfinding package
 Adding pathfinding functionality in the scene
 Create empty object
 Name it “A* Pathfinder”
 Add the AstarPath script from Aron’s package
 This is a unique central hub for computing paths
 Adding pathfiding functionality to the character
 Add the Seeker component

13. Pathfinding: Ex. in Unity
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 Specify the parameters of the
AstarPath script
 Grid Graph
 Position/size
 4-connected/8-connected
 Cut corners
 Collision testing
 Type/size of collider
 Mask: Use Obstacle Layer
 Scan and observe!

14. Pathfinding: Ex. in Unity
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 Capsule collider with diameter 2
 8-connected

15. Pathfinding: Ex. in Unity
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 Capsule collider with diameter 2
 8-connected
“Cut corners”
option affects
these edges

16. Pathfinding: Ex. in Unity
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 Capsule collider with diameter 6
 4-connected

17. Pathfinding: Examples in Unity
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 Using the Seeker script to get paths for Lerpz
 Astar AI1
 Astar AI2
 Astar AI3
 Astar AI4
 Based on sample code in Aron’s pathfinding package

18. Pathfinding: Examples in Unity
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 Using the Seeker script to get paths for Lerpz
public class AstarAI1 : MonoBehaviour {
public Vector3 targetPosition;
public void Start () {
//Get a reference to the Seeker component
Seeker seeker = GetComponent<Seeker>();
//Start a new path to the targetPosition,
//return the result to the OnPathComplete function
seeker.StartPath (transform.position,targetPosition,
OnPathComplete);
}
public void OnPathComplete (Path p) {
Debug.Log ("Yey, we got a path back!");
}
}

19. Pathfinding: Examples in Unity
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 Astar A1 script calls the Seeker's StartPath function
 The Seeker creates a new Path instance and sends it to
the AstarPath script (in the A* Pathfinder game-object)
 AstarPath script puts the path in a queue, when
available, it processes the path by searching the grid in
the A* heuristic search manner we described earlier
 AstarPAth script calls the function OnPathComplete with
the path it found as a parameter p
 p.VectorPath holds a list of Vector3 objects that show
how the destination can be reached

20. Pathfinding: Examples in Unity
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 Seeker option to display path via gizmos

21. Pathfinding: Examples in Unity
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 Post-processing path via modifiers (here: Funnell mod.)

22. Pathfinding: Examples in Unity
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 Using Astar AI1 script, Lerpz is able to find out how
to get to the target object (fuel cell prefab)
 So, let’s make Lerpz move!
 Accessing other components
(docs.unity3d.com:Accessing)
 SimpleMove function of Character component
(docs.unity3d.com:CharacterController.SimpleMove)
 FixedUpdate instead Update for physics-related things
(docs.unity3d.com:FixedUpdate,
unity3d.com/tutorials:Update-and-Fixedupdate)

23. Pathfinding: Examples in Unity
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public class AstarAI2 : MonoBehaviour {
...
//The calculated path
public Path path;
//The character’s speed
public float speed = 100;
//The distance to a waypoint for moving to the next
public float nextWaypointDistance = 3;
//The waypoint we are currently moving towards
private int currentWaypoint = 0;
public void Start () {
... }
public void OnPathComplete (Path p) {
... }
public void FixedUpdate () {
... }
}

24. Pathfinding: Examples in Unity
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public class AstarAI2 : MonoBehaviour {
public void FixedUpdate () {
//Check if we reached the destination
if (currentWaypoint >= path.vectorPath.Count) {
Debug.Log ("End Of Path Reached");
return;
}
//Direction to the next waypoint
Vector3 dir = (path.vectorPath[currentWaypoint]-
transform.position).normalized;
dir *= speed * Time.fixedDeltaTime;
controller.SimpleMove (dir);
//Check if we need to switch to the next waypoint
if (Vector3.Distance(transform.position,
path.vectorPath[currentWaypoint]) < nextWaypointDistance) {
currentWaypoint++;
return;
}
}

25. Pathfinding: Examples in Unity
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 Lerpz moves but without animating its parts
 Basic animation of pre-defined clips
 Animation component (docs.unity3d.com:Animation)
 Play(“walk”), Stop()

26. Pathfinding: Examples in Unity
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 Lerpz.fbx
 Embedded animations that have
been created outside of Unity for
the 3D model
 Available for
 Playing
 Looping
 Blending

27. Pathfinding: Examples in Unity
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public class AstarAI3 : MonoBehaviour {
...
//Cashed reference to Animation component
public Animation anim;
public void Start () { ...
anim = transform.GetComponentInChildren<Animation>();
}
public void OnPathComplete (Path p) { ...
anim.Play("walk");
}
public void FixedUpdate () { ...
if (currentWaypoint >= path.vectorPath.Count) {
Debug.Log ("End Of Path Reached");
anim.Stop();
return;
...
}
}
}

28. Pathfinding: Examples in Unity
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 We can do better than that!
 Turn when changing direction while moving
 Slow down before reaching destination
 Nicer/smoother paths
 Plan/replan for a moving target
 Plan/replan with a dynamic grid

29. Pathfinding: Examples in Unity
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 We can do better than that!
 Astar AI4 script
 Target is a transform of an object in the game-world
 Repath rate
 Turning speed
 Slowdown distance
 Fancy code with coroutines and yield
(docs.unity3d.com:Coroutines-Yield)

30. Pathfinding: Examples in Unity
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 We can do better than that!
 TargetMover script attached on main camera
 Moves target to position of mouse
 Always on or only when double click is detected
 Use the fuel cell as a target
 ObjectPlacer script attached on main camera
 Pressing “p” adds a game-object instance at ray collision
with a game-object in the scene
 Use it to place crates
 Pressing “r” removes game-object

31. Pathfinding: Examples in Unity
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public class TargetMover : MonoBehaviour {
...
//Handle continuous move in Update() function
void Update () {
if (!onlyOnDoubleClick && cam != null) {
UpdateTargetPosition ();
}
}
public void UpdateTargetPosition () {
//Define a ray from eye to mouse position
Ray ray = cam.ScreenPointToRay (Input.mousePosition);
//Do raycast and if it hits the given mask layer
RaycastHit hit;
if (Physics.Raycast(ray, out hit, Mathf.Infinity, mask)){
//transport the target at the hit position
target.position = hit.point;
}
}

32. Pathfinding: Examples in Unity
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public class ObjectPlacer : MonoBehaviour {
...
void Update () {
if (Input.GetKeyDown ("p")) {
PlaceObject ();
}
if (Input.GetKeyDown ("r")) {
RemoveObject ();
}
public void PlaceObject () {
//Cast a ray, etc
...
}
public void RemoveObject () {
//Cast a ray, etc
...
}
}

33. Pathfinding: Examples in Unity
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 Scripts
 Astar AI1
 Astar AI2
 Astar AI3
 Astar AI4
 TargetMover
 ObjectPlacer
 Either as originally from Aron’s Pathfinding Project or
with slight modifications
 Use the ones in the project in Pathfinding.zip

34. Pathfinding: Examples in Unity
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 Many crates

35. Pathfinding: Examples in Unity
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 Many crates – How does Lerpz know to avoid them?

36. Pathfinding: Examples in Unity
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public void PlaceObject () {
Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
RaycastHit hit;
//If we hit an object
if ( Physics.Raycast (ray, out hit, Mathf.Infinity)) {
Vector3 p = hit.point;
//Instantiate a new game-object
GameObject obj = (GameObject)GameObject.Instantiate
(go,p,Quaternion.identity);
//Update the pathfinding graph
Bounds b = obj.collider.bounds;
GraphUpdateObject guo = new GraphUpdateObject(b);
AstarPath.active.UpdateGraphs (guo);
}
}

37. Pathfinding: Examples in Unity
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 Local updates are faster if we have a huge map
 But can be problematic when objects end up farther
away or may fall on the ground later than the update

38. Pathfinding: Examples in Unity
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 Many Lerpzs!

39. Pathfinding: Examples in Unity
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 Many Lerpzs! FPS decreases even for just 10 NPCs

40. Pathfinding: Examples in Unity
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 Grids can only go so far

41. Pathfinding: Examples in Unity
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 Open scene “Pathfiding on platforms”

42. Pathfinding: Unity
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 Height testing
 Similar to obstacles
 Use “Ground” layer to identify
areas that are walkable
 Raycasting

43. Pathfinding: Examples in Unity
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 We can still tweak our grid to do the job

44. Pathfinding: Unity
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 Or we can use a graph (Pointgraph, dist=4)

45. Pathfinding: Unity
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 Or we can use a graph (Pointgraph, dist=4)

46. Pathfinding Part 3: Beyond the basics
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 Many neat tricks for efficient/nice pathfinding
 Alternative game-world representations
 Beyond A*
 Better heuristics