1. Behavior trees & The C# programming language for Java programmers
CS 185C
Behavior trees
&
The C# programming language
for Java programmers

2. In this day in Video Games...

3. State-Based Scripting – Behavior Trees
Allows ”choose the highest priority of the following states”
Allows ”do the following states in order”
Can execute multiple states at a time
Each state knows if it is relevant or not
Can sequence states

4. State-Based Scripting – Behavior Trees
Cutman

5. State-Based Scripting – Behavior Trees
Each node can be successful, failed, or in progress
Different node types (shapes) have different rules

6. State-Based Scripting – Behavior Trees
Harder to write
Easier to understand and modify
Easy to change different node priorities
Easy to break a node up into two steps

7. State-Based Scripting – Behavior Trees
Same Batman boss characters

8. Questions?

9. Unity3D Scripting UnityScript JavaScript-inspired
JavaScript is commonly used for web page scripting
Internally, everything is using .NET via Mono

10. Unity3D Scripting C# Most popular .NET language
Static typed, object oriented
”Microsoft Java”
Microsoft has added a lot of nifty new syntax, but Unity's version lags behind

11. C# Example using UnityEngine; using System.Collections;
public class BackAndForthClass : MonoBehaviour {
public float speed = 6;
// Update is called once per frame
void Update() {
if( transform.position.x > 40 || transform.position.x < -40 ) {
transform.Rotate( 0, 180, 0 );
transform.Translate( -10, 0, 0 );
speed = Random.Range( 6f, 10f ); }
transform.Translate( -speed * Time.deltaTime, 0, 0 );

12. C# Overview Almost exactly the same as Java Classes Methods Members
Public vs Private
Comments
Primitive Types
Branching, Loops
Interface

13. C# - Classes Represent a ”behavior” or concept
In Unity most classes inherit from MonoBehavior
public class CLASSNAME : PARENT {
public float MEMBER = 6;
int ANOTHER_MEMBER = 0;
void METHOD() {
// code would go here }
public float OTHER_METHOD(float PARAM1, float PARAM2) {

14. C# - Comments Note for humans, ignored by the computer
// A single line comment
/* A different single line comment */ /*
A mulitple
line comment */

15. C# - Types bool true or false (boolean in Java) int number (1, 2, 3)
float numer with a decimal point (2.5, 3.14)
string text (String in Java)
object an unknown thing (Object in Java)
Array a collection of objects
Vector3 3D position
Quaternion 3D rotation

16. C# - Branching, Loops Do things conditionally, or multiple times
if( CONDITION ) {
// Stuff only run if condition is true
} else if( CONDITION2 ) {
// Stuff only run if condition2 is true, condition is false
} else {
// Stuff run if condition and condition2 are both false }
while( CONDITION ) {
// Stuff run until condition becomes false
for( INIT; CONDITION; INCREMENT ) {
// Stuff run until condition becomes false, useful for arrays

17. C# - Branching, Loops Do things conditionally, or multiple times
if( CONDITION ) {
// Stuff only run if condition is true
} else if( CONDITION2 ) {
// Stuff only run if condition2 is true, condition is false
} else {
// Stuff run if condition and condition2 are both false }
while( CONDITION ) {
// Stuff run until condition becomes false
for( INIT; CONDITION; INCREMENT ) {
// Stuff run until condition becomes false, useful for arrays

18. C# - Event Handling Events in Unity are just method calls
Important events:
Update
FixedUpdate
OnTriggerEnter
OnCollisionEnter
Many other ”OnX”

19. C# Example using UnityEngine; using System.Collections;
public class BackAndForthClass : MonoBehaviour {
public float speed = 6;
// Update is called once per frame
void Update() {
if( transform.position.x > 40 || transform.position.x < -40 ) {
transform.Rotate( 0, 180, 0 );
transform.Translate( -10, 0, 0 );
speed = Random.Range( 6f, 10f ); }
transform.Translate( -speed * Time.deltaTime, 0, 0 );

20. C# Example using UnityEngine; using System.Collections;
public class BackAndForthClass : MonoBehaviour {
public float speed = 6;
void Update() {
transform.Translate( -speed * Time.deltaTime, 0, 0 ); }
void OnTriggerEnter( Collider c ) {
transform.Rotate( 0, 180, 0 );
transform.Translate( -10, 0, 0 );
speed = Random.Range( 6f, 10f );

21. Questions?

22. C# - struct
Looks and acts just like a class, EXCEPT when passed to a function, it is copied
Allocated on the stack as opposed to the heap
public struct Vector3 {
public float x;
public float y;
public float z;
// helper methods
public void Normalize() {
// code goes here }

23. C# - Operator Overloading
Lets you use math symbols (+, -, *, /) instead of calling methods.
Vector3
operator+
operator-
operator*
operator/
operator==
operator!=

24. C# - Properties Make things look like fields but behave like methods.
public float Length {
get { return Mathf.Sqrt( x*x + y*y + z*z ); }
set {
float old = Mathf.Sqrt( x*x + y*y + z*z );
float scale = value / old;
x *= scale; y *= scale; z *= scale; }

25. C# - goto C# supports goto. Goes to a specific named label.
public object findAndProcessDuplicate(object[] a) {
for( int i = 0; i < a.Length; i++ ) {
for( int j = i + 1; j < a.Length; j++ ) {
if( a[i] == a[j] ) {
Process(a[i]);
goto done; }
done:
afterProcessing();

26. Questions?

27. Let's look at a real example.C#
Let's look at a real example.