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SE 320 – Introduction to Game Development

Lecture 7: ProgrammingLecturer: Gazihan Alankuş

Please look at the last two slides for assignments (marked with TODO)

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Sample Games in Homework

• URL was: http://u3d.as/content/m2h/c-game-examples/1sG

• What were the things that you found interesting?

• What have you learned?• What were your issues?– Let’s quickly go over the games– Jump in when we are close to your question!

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How does a game work?

• You write code– that is able to manipulate the game world

• That code is ran– at certain points in time

• You manipulate game state

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Game State

• Examples– HP (life)– Ammo– Inventory items– Cool-down time for a skill– Experience

• More examples from actual games

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Implementing State

• Variables in your custom componentspublic class LifeManager : MonoBehaviour {

public float HP;}

• The instance of the component will reflect state of the game object that it is attached to.– Different instances of your prefab will have

different values for the state variables

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Implementing State

• Locality of state – which component should keep which state?– One component that keeps HPs of all characters in

the game? – Every character keeps his own HP?

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Accessing Objects in the Scene• Getting another game object

– GameObject enemy = GameObject.Find(“enemy”); //or the one below

– public GameObject enemy; //drag to this• Getting a component

– Attached to the same game object• MyComponent c = GetComponent<MyComponent>();

– Attached to some other game object• MyComponent c = enemy.GetComponent<MyComponent>();

• Using parent/child relationships– Transform parentsTransform = transform.parent;– GameObject parent = transform.parent.gameObject;

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Accessing Objects in the Scene

• It’s slow to keep calling GameObject.Find(“..”) • Make connections in the Awake function

public class Player: MonoBehaviour {GameObject enemy;void Awake() {

enemy = GameObject.Find("enemy");}

}

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Data Types in Unity

• Some standard data types– Vector3 (position, direction, displacement)– Quaternion (orientation, rotation)

• Details of standard components– Transform, Collider, Renderer, RigidBody

• Basic data structures in C#– List, Dictionary, etc.

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Vector3

• Vector3 means “three dimensional vector”• Just three floats: x, y and z• Often used for talking about a 3D position or

direction– Contains methods/properties that help in this

domain• e.g., transform.position is a Vector3

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Vector3: related to magnitude

• v.normalized• v.magnitude• v.Normalize

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Vector3: some constants

• Vector3.zero == new Vector3(0, 0, 0)• Vector3.one == new Vector3(1, 1, 1) (LOL)• Vector3.forward == new Vector3(0, 0, 1)• Vector3.back == new Vector3(0, 0, -1)• Vector3.up == new Vector3(0, 1, 0)• Vector3.down == new Vector3(0, -1, 0)• Vector3.right == new Vector3(1, 0, 0)• Vector3.left == new Vector3(-1, 0, 0) 2/10/2012

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Vector3: Averaging (interpolating)

• Vector3.Lerp(v1, v2, fraction)

• Vector3.Slerp(v1, v2, fraction)

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v1 v2

0 fraction 1

v1 v2

0fraction

1

origin (0, 0, 0)

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Vector3: Geometric operations

• Vector3.Scale(v, s)• Vector3.Project(v, vbase)• Vector3.Angle(v1, v2)• Vector3.Distance(v1, v2)• Vector3.Dot(v1, v2)• Vector3.Cross(v1, v2)

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Vector3: operators

• v1 + v2 – Adds x, y, z values separately and returns the sum

vector• 3.5 * v– Multiplies x, y, z with 3.5

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Quaternion

• Has four values (x, y, z, w). What are they?– Don’t worry about its mathematical definition (has four

values, etc. don’t care because they won’t make sense in our context)

• Is simply (both of these below are true)– A vector and an angle

• Rotate around that vector with that angle– Three consecutive rotations around z, x and y axes

• Represents– Orientation (rotate to here from default orientation)– Rotation (change in orientation)

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Quaternion

• q.x, q.y, q.z, q.w– DON”T CARE!!!1!!!– NEVER USE THEM!!!!! >:@

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Quaternion: its value that makes sense

• q.eulerAngles– Vector3 that contains rotations around axes– Rotation order is z, x, y (but you don’t have to

care)• q.ToAngleAxis(out angle, out axis)– sets the angle and axis variables that you give to it– rotation around that axis with that angle amount

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Quaternion: operations• q1 * q2

– the result is the rotation that is equal to: rotate with q2 first, and then with q1

– or, if q2 is orientation of something, rotates it with q1 (same thing, slightly different interpretation)

• q * v– rotate v with q

• Quaternion.Dot(q1, q2)• Quaternion.AngleAxis(angle, axis)• Quaternion.Euler(x, y, z)• Quaternion.Inverse(q)• ...

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Quaternions: Averaging (interpolating)

• Quaternion.Slerp(q1, q2, fraction)– The correct way to interpolate two quaternions

• Quaternion.Lerp(q1, q2, fraction)– Slightly faster, bad interpolation (moves faster in

the middle)

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There are more

• Ray, Rect, Vector2, Vector4, etc.• Use the scripting reference

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Standard components

• Have – Properties (variables)

• Can’t modify• Can set for an instance

– Functions• Can call for an instance

– Class functions (static)• Can call with the class name, without an instance

– Messages• Functions are called on all components that are attached to

the GameObject when events happen (via SendMessage)

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Transform• transform.position• transform.rotation

– With respect to the world. Changes when parent changes.– Not what you see in the inspector.

• transform.localPosition• transform.localRotation• transform.localScale

– With respect to the parent. Does not change when parent changes.– What you see in the inspector

• transform.right, transform.up, transform.forward – x, y, z axes of the orientation (the arrows you see)

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Global vs. Local

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p

c

p.position ==

p.loca

lPositi

on

c.localPosition

c.position

c.transform.parent == p.transform

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Global vs. Local

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p

c

p.position == p.lo

calPosition

c.localPosition

c.position

Red ones changed as a result of moving the parent

All of this is the same for rotation and localRotation

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Renderer

• r.material• r.isVisible

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Colliders

• c.isTrigger– True• Not used in physics calculations, lets things through• OnTriggerEnter is sent to the GameObject (and its

components)– False• Used in physics calculations, won’t let things through• OnCollisionEnter is sent to the GameObject (and its

components)

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Colliders

• c.material– The physics material (PhysicMaterial)• friction constants• bounciness

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Standard components• Have

– Properties (variables)• Can’t modify• Can set for instance

– Functions• Can call for instance

– Class functions/class variables (static)• Can use with class name, without

an instance. Like global variables but in class.

– Messages• Functions are called on all

components that are attached to the GameObject when events happen

• Examples– t.position = t.position + Vector3.up;

– t.Translate(1, 1, 1)

– Vector3.Lerp(v1, v2, f)– Vector3.up

– Update()– OnCollisionEnter() – OnCollisionEnter(Collision collision)

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There are many other components

• Use the scripting reference!

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Collection Data Structures in C#• using System.Collections;

using System.Collections.Generic;

• List<GameObject> enemies = new List<GameObject>();– loop with foreach, access enemies[5]

• Dictionary<string, GameObject> enemiesByName = new Dictionary<string, GameObject>();– access by enemy name.

enemiesByName[“wolf”]– loop with foreach

• Amazing resource: http://www.dotnetperls.com/• Also should watch:

http://channel9.msdn.com/Series/C-Sharp-Fundamentals-Development-for-Absolute-Beginners/Working-with-Collections-21

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Game Structure• You will have GameObjects for various elements in your game (character,

enemy, robot, etc). Create their own scripts and put code specific for them.• You also need to have code that is common for the game (scoring is an

example). Attach such scripts on the camera or on a similarly unique object.• Wire them up in Awake()• For common singletons, create

– static MyScript instance;– public static MyScript getInstance() { return instance; }– public MyScript() { instance = this; }

• And in other scripts, – MyScript myScript = MyScript.getInstance();– Easier than GameObject.Find()

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TODO: Homework• Start with your own Homework 3 (ask the assistant if you haven’t done it)• Add a bullet prefab that you will use to make your character throw bullets• You already should have a monster prefab. Add a 3D text over its head that you will use to display

the monster’s remaining life percentage. • Create a MonsterLifeManager component that will handle changing and displaying life of the

monster that it’s attached to. • Make it so that the space key will throw a bullet towards which your character is facing

(transform.forward). The bullet needs to remember this initial direction and should move proportional to time at each frame (update) towards this direction.

• When a bullet hits a monster, it should reduce its life by a random value between 5 and 10. Initially life is 100. When life gets to zero, the monster disappears.

• You should have at least three monsters in the scene• Bonus: reduce monster’s life depending on the body part that is hit (headshot, etc.)• Get Özkan to grade it

– ozkansayin.ieu@gmail.com – Subject (paste this): SE 320 Homework 7– What to send:

• Assets -> Export package • File -> Build Settings -> Web player -> Build