Unit 12.3A · Term 3

Sprites & Characters

Sprites are 2D images that represent game characters, enemies, and items. PyGame's Sprite class lets you organize game objects with their own image, position, and behavior.

Learning Objectives

12.5.2.2 Create characters for the application
12.5.3.5 Code sprite management

Lesson Presentation

12.3A-sprites-characters.pdf · Slides for classroom use

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Conceptual Anchor

The Actor Analogy

A Sprite is like an actor in a play: it has a costume (self.image), a position on stage (self.rect), and a script (update() method). A Group is the cast list — it manages all actors at once.

Rules & Theory

Loading Images

Method	Purpose
`pygame.image.load("file.png")`	Load image from file
`.convert()`	Optimize for display (no transparency)
`.convert_alpha()`	Optimize with transparency support (PNG)
`pygame.transform.scale(img, (w,h))`	Resize image
`pygame.transform.flip(img, H, V)`	Flip horizontally/vertically
`pygame.transform.rotate(img, angle)`	Rotate by degrees (counter-clockwise)

The Sprite Class Template

class Player(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        # self.image = the visual appearance
        self.image = pygame.Surface((40, 40))
        self.image.fill((255, 50, 50))
        # self.rect = position and collision box
        self.rect = self.image.get_rect(center=(x, y))
        self.speed = 5

    def update(self):
        """Called every frame by the group."""
        keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT]:
            self.rect.x -= self.speed
        if keys[pygame.K_RIGHT]:
            self.rect.x += self.speed

Sprite Groups

Method	Purpose
`group = pygame.sprite.Group()`	Create an empty group
`group.add(sprite)`	Add a sprite to the group
`group.remove(sprite)`	Remove a sprite from the group
`group.update()`	Call `update()` on ALL sprites
`group.draw(surface)`	Draw ALL sprites onto surface
`sprite.kill()`	Remove sprite from ALL groups

Worked Examples

1 Player Sprite with Image

import pygame, sys

pygame.init()
WIDTH, HEIGHT = 800, 600
screen = pygame.display.set_mode((WIDTH, HEIGHT))
clock = pygame.time.Clock()

class Player(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        # Load image OR create colored surface
        self.image = pygame.Surface((50, 50))
        self.image.fill((0, 200, 100))
        self.rect = self.image.get_rect(center=(400, 300))
        self.speed = 5

    def update(self):
        keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT]:  self.rect.x -= self.speed
        if keys[pygame.K_RIGHT]: self.rect.x += self.speed
        if keys[pygame.K_UP]:    self.rect.y -= self.speed
        if keys[pygame.K_DOWN]:  self.rect.y += self.speed
        self.rect.clamp_ip(screen.get_rect())

# Create sprite and group
player = Player()
all_sprites = pygame.sprite.Group(player)

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    all_sprites.update()

    screen.fill((30, 30, 30))
    all_sprites.draw(screen)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()
sys.exit()

2 Spawning Enemies

import pygame, sys, random

class Enemy(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.Surface((30, 30))
        self.image.fill((255, 50, 50))
        # Spawn at random x, above screen
        self.rect = self.image.get_rect(
            center=(random.randint(30, 770), -30)
        )
        self.speed = random.randint(2, 5)

    def update(self):
        self.rect.y += self.speed
        if self.rect.top > 600:
            self.kill()  # remove when off screen

# Usage in game loop:
enemies = pygame.sprite.Group()

# Spawn enemy every 60 frames
frame_count = 0
# inside loop:
frame_count += 1
if frame_count % 60 == 0:
    enemies.add(Enemy())

enemies.update()
enemies.draw(screen)

Common Pitfalls

Forgetting super().init()

Always call super().__init__() in your Sprite subclass. Without it, the sprite won't work with groups.

Missing .convert_alpha()

When loading PNG images with transparency, use .convert_alpha(). Plain .convert() loses the transparent background.

Tasks

Apply

Create a Player sprite that moves with arrow keys and stays within screen bounds.

Apply

Add 10 randomly positioned "coin" sprites (yellow circles) to the screen using a Group.

Create

Create enemies that spawn at the top and fall down. Use kill() to remove them when they exit the screen.

Self-Check Quiz

Q1: What two attributes must every Sprite have?

self.image (the visual surface) and self.rect (position and collision box).

Q2: What does group.update() do?

Calls the update() method on every sprite in the group — used to move, animate, or update state for all objects at once.

Q3: How do you remove a sprite from the game?

sprite.kill() — removes it from all groups it belongs to, effectively removing it from the game.