PyGame - Unit 4

PyGame Unit 4

4.1 – Object Oriented Programming

OOP

PyGame - Unit 4

Text Book for OOP Module

• Introduction to Computer Science Using Python and PyGame– By Paul Vincent Craven

• It should already be on your network drive.

• Easily found on the Internet:– http://cs.simpson.edu/files/CS_Intro_Book.pdf

PyGame - Unit 4

PyGame – 4.1

Introduction to Object Oriented Programming (OOP)

PyGame - Unit 4

Objectives• By the end of this unit you will be able to:

– Define an object and how it is useful to programmers.

– Describe a class and how it relates to programming objects

– Describe methods and how they relate to classes and functions

– Create and use Classes, Methods and Objects.

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What is an Object• A software construct that allows data to be

merged with its related programming logic.

• A thing that can perform a set of related activities.

• Example object: Zombie:– Data/Properties: health; attackPower; etc.– Activities: walk; attack; climb; etc.

Properties and Methods

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• Why can’t they make up their minds?

• Properties = variables or attributes

• Methods = functions

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Object Example Shooter “1943”

Airplane Object:

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Airplane Object in “1943”Example: • “1943” (A classic top-down shooter game)

– Object: airplane• Properties (Data) - speed; health; shields; image• Methods (functions) – move; fire; shield

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Class• Blueprint for constructing objects

• Programming code and data used to create one or more objects.

• The code is broken into functions called Methods.

• The official term for the data is Properties.

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Classes are like Blueprints• Blueprint = design for one or more homes:

• Class = design for one or more objects:

Class EnemyPlane:…

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Class DiagramsClass Name:

Data:

Methods: (functions)

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Creating Objects• Instance – The name of an object in memory.

Format:

objectVariableName = ClassName()

Example:

enemyObj = EnemyPlane()

– Note: the suffix Obj is not necessary, it helps us remember that it is an object instance.

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Object Instances

enemyObj = EnemyPlane()

enemyObj – can be any name you like– Points to the place in memory where the

object instance exists.

Instance Example (Dog Class)• Dog is the class:• Rayne is the object instance:

• After the Rayne object instance is created, it has the same properties and access to the methods defined in the class.

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Defining our Ship Class (data)

Class Ship: speed = 5 health = 20

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The getSpeed() Method (function)

class Ship: speed = 5 health = 20

getSpeed() return self.speed

• Why self.speed???

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Creating an Instance of “Ship” Object

• Creating the shipObj instance.shipObj = Ship()

• Printing the health for the shipObjprint(shipObj.health)

Returns: 20 (the default value set within the class)

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Modifying a Object’s Parameter

shipObj = Ship()

• Making shipObj very healthyshipObj.health = 500

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Multiple Object Instancesclass EnemyShip:speed = 4health = 15

enemyObj1 = EnemyShip()enemyObj2 = EnemyShip()enemyObj3 = EnemyShip()

enemyObj1.speed = 5enemyObj2.speed = 6enemyObj3.speed = 7

print(enemyObj1.speed, enemyObj2.speed, enemyObj3.speed)

Returns: 5 6 7

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The Power of OOP

• Instantiation (ie. multiple enemies)• Objects can be passed into functions

– Printing the data of shipObj:

printShipData(shipObj)• Sprites

– Displaying and moving images on screen– Collision detection– Sprite Groups:

• Putting sprites in a list (Supports displaying, updating and collision detection)

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• Read the textbook entitled “Introduction to Computer Science Using Python and PyGame”– Read CH 13 PP. 105 – 112– 4-1 Exercises

• See the Intranet for exercise details:

Reading / Exercises

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PyGame – 4.2

Object Oriented Programming (OOP)Inheritance and Constructors

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Objectives• By the end of this unit you will be able to:

– Define inheritance and constructors as they apply to object oriented programming.

– Utilize constructor methods to execute programming logic when an object is instantiated.

– Create a class that inherits the methods and properties of another class.

Constructor

• Constructor – A special function that is called any time an instance of that class is created.

» Courtsey of Borderlands 2

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Constructor

• Runs only once; only when the object is first created (instantiated)

• May be used to:– Get information from data source– Create variables– Etc.

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Sample Constructor• “A new dog is born!” is printed when an instance of

Dog() is created.

class Dog(): # Constructor # Called when creating an object of this type

def __init__ (self): print ("A new dog is born !")

# Create the myDog object from the Dog()class.

myDog = Dog()

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Constructor Input Parameterclass Dog(): name = '' def __init__ (self, newName): self.name = newName

# Create the myDog object from the# Dog()class.myDog = Dog('Spot')print (myDog.name) # Prints “Spot”

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Constructors and selfclass Dog (): name = 'Rover' # Only useful the first time

def __init__ (self , name): # This will print "Rover" print (self.name) # Stays in memory until object is deleted.

# This will print "Spot" print(name)

# Create the myDog objectmyDog = Dog('Spot')

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Selfclass Dog (): self.breed = 'Mutt' # Stays in memory until object is deleted.

def __init__ (self ): # This will print "Rover" print (self.breed)

# Create the myDog objectmyDog = Dog()

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Inheritance

• Inheritance – When a class copies all methods and properties from another class.

• Sprite class– Our custom classes will inherit the methods

and properties of the Sprite class.

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Inheriting From the Person Class

• Customer and Employee inherit the methods and parameters of the Person class.

• Parent Class – Person• Child Classes – Employee; Customer

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Inheritance Example

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class Person (): self.name = ''

class Employee (Person): self.job_title = ''

class Customer (Person): self.email =''

johnSmith = Person ()johnSmith.name = 'John Smith'

janeEmployee = Employee ()janeEmployee.name = 'Jane Employee'janeEmployee.jobTitle = 'Web Developer'

bobCustomer = Customer ()bobCustomer.name = 'Bob Customer'bobCustomer.email = 'send_me@spam.com'

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• Pg4-2-0: Read PP. 112-117 from the "Introduction to Computer Science Using Python and PyGame" text.

• 4-2-1 (Class constructors)• 4-2-2 (Inheritance)

• See the Intranet for exercise details:

Reading / Exercises

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PyGame – 4.3

PyGame SpritesAn Introduction

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Objectives• By the end of this unit you will be able to:

– Define a Sprite and describe how it is used in 2d games.

– Create a class that inherits the Sprite class.

– Create an instance of the class that inherits from Sprite.

Sprite

• Sprite – 2 dimensional image that is part of a larger graphical scene.

• Originally supported by hardware• Used for:

– Animation– Collision detection– Managing groups of sprites– Much Much more…

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Inheriting from a Sprite

• The Player class inherits all methods and properties of the Sprite class.

• The Sprite class is in the pygame.sprite module.

# *** Player Class ***class Player(pygame.sprite.Sprite):

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Call Sprite constructor

• Call the constructor for the Sprite from within the class that is based upon Sprite.– Allows all sprites to initialize

# *** Player Class ***class Player(pygame.sprite.Sprite):

def __init__(self): # Call the parent class (Sprite) constructor

pygame.sprite.Sprite.__init__(self)

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Example (Player Class)# *** Player Class ***class Player(pygame.sprite.Sprite): def __init__(self): # Call the parent class (Sprite) constructor pygame.sprite.Sprite.__init__(self)

# Set the image and rect variables self.image = pygame.image.load(PLYR_SHP).convert() self.rect = self.image.get_rect()

playerObj = Player() # Create an instance of “Player”playerObj.rect.x = 10 # Set the x coordinateplayerObj.rect.y = 400 # Set the y coordinate

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• Pg4-3-0: Read PP. 119-123 from the "Introduction to Computer Science Using Python and PyGame" text.

• 4-3-1 (Create the Triangle class)– See the Intranet for exercise details:

Reading / Exercises

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PyGame – 4.4

PyGame SpritesSprite Groups; Moving Groups of Sprites; Collision Detection

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Objectives• By the end of this unit you will be able to:

– Create Sprite Groups

– Use Sprite Groups to move sprites on the screen.

– Define collision detection

– Use Sprite Groups to implement collision detection

Sprite Groups• Sprite Group – A PyGame feature that assists

us with working with more than one sprite.• Why Sprite Groups:

– Collision Detection: Determining if a sprite in one group collides with a sprite in another group.

• Or if a non-grouped Sprite collides with a sprite in a group.

– Group Updates: Calling update() method for all sprites in the group with one command.

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Adding a Sprite to a GroupallSpritesGroup = pygame.sprite.Group()

# *** Enemy Class ***class Enemy(pygame.sprite.Sprite): def __init__(self): # Call the parent class (Sprite) constructor pygame.sprite.Sprite.__init__(self)

# Set the image and rect variables self.image = pygame.image.load(ENEMY_SHIP).convert() self.rect = self.image.get_rect()

enemyObj = Enemy()# Create an instance of “Enemy”enemyObj.rect.x = 10 # Set the x coordinateenemyObj.rect.y = 400 # Set the y coordinateallSpritesGroup.add(enemyObj)

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Sprite Groups (Enemy Class)allSpritesGroup = pygame.sprite.Group()# *** Enemy Class ***class Enemy(pygame.sprite.Sprite): def __init__(self, color): # Call the parent class (Sprite) constructor pygame.sprite.Sprite.__init__(self) self.image = pygame.image.load(ENEMY_SHIP_1).convert() self.rect = self.image.get_rect()

enemyObj = Enemy() # Create an instance of “Enemy”enemyObj.rect.x = 10 # Set the x coordinateenemyObj.rect.y = 400 # Set the y coordinate

allSpritesGroup.add(enemyObj)•Several instances of the Enemy class are placed in the allSpritesGroup.

– allSpritesGroup is used for collision detection and moving sprites on the screen.

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Updating using Sprite Groupsclass Enemy(pygame.sprite.Sprite):

def __init__(self, color): # Call the parent class (Sprite) constructor pygame.sprite.Sprite.__init__(self) self.image = pygame.image.load(ENEMY_SHIP_1).convert() self.rect = self.image.get_rect()

def update(self): self.rect.y += 5

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Updating and Drawing Sprite Groups

# Update enemyGroup to move enemy ships.enemyGroup.update()

# Clear the screenDISPLAYSURF.fill(WHITE)

# Draw all enemy sprites in enemyGroupenemyGroup.draw(DISPLAYSURF)

fpsClock.tick(FPS)pygame.display.flip()

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Exercise

• Do PyGame exercise 4-4-1. You can find the details on the Intranet.

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Collision Detectionpygame.sprite.groupcollide(group1, group2, True, True)

•Group1 = The first sprite group to compare•Group2 = The second sprite group to compare•True (the first one) = Delete objects in group 1 that have collided with objects in group 2.•True (the second one) = Delete objects in group 2 that have collided with objects in group 1.

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Exercise

• Do PyGame exercise 4-4-2. You can find the details on the Intranet.

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