Alien Invasion Game

A fun 2D space shooter game built with Python and Pygame. Defend your ship from waves of invading aliens!

Game Overview

Alien Invasion is a classic arcade-style shooter where you:

• Control a ship at the bottom of the screen using LEFT and RIGHT arrow keys
• Shoot aliens with the SPACE bar
• Survive waves of aliens that move horizontally and descend toward you
• Earn points for each alien destroyed
• Lose when aliens reach the bottom or hit your ship
• Progress through increasingly difficult levels

Features

✅ Player Controls

• Arrow keys for smooth left/right movement
• Space bar to fire bullets (max 3 on screen)
• Press P to restart after game over
• Press Q to quit

✅ Game Mechanics

• Fleet of aliens that move horizontally and drop down when hitting screen edges
• Collision detection for bullets hitting aliens
• Collision detection for aliens hitting the ship
• Game over when all lives are lost
• Level progression with increasing difficulty
• Score tracking and lives display

✅ Visual Elements

• Sky blue background
• Ship sprite at the bottom
• Green alien sprites in formation
• Black bullet indicators
• Game over screen with restart instructions
• On-screen score and lives counter

Installation

Prerequisites

• Python 3.7 or higher
• uv package manager

Installing uv

If you don't have uv installed, follow the official uv installation guide:

macOS/Linux:

curl -LsSf https://astral.sh/uv/install.sh | sh

Windows:

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

Or install via Homebrew (macOS):

brew install uv

For other installation methods, see the uv documentation.

Setup

1. Navigate to the project directory:

cd alien-invasion

2. Install dependencies:

uv sync

3. Generate the alien sprite image (if not already created):

uv run create_alien_image.py

Running the Game

uv run alien_invasion.py

The game window will open at 1200x800 resolution.

Game Controls

Key	Action
LEFT Arrow	Move ship left
RIGHT Arrow	Move ship right
SPACE	Fire bullet
P	Play again (when game over)
Q	Quit game

Game Settings

You can customize game parameters in settings.py:

• Screen resolution: screen_width, screen_height
• Ship speed: ship_speed
• Bullet settings: bullet_speed, bullet_width, bullet_height, bullets_allowed
• Alien settings: alien_speed, fleet_drop_speed
• Difficulty scaling: speedup_scale (multiplier for speed increase per level)

Example: Making the game harder

self.ship_speed = 2.0          # Faster ship
self.alien_speed = 2.0         # Faster aliens
self.speedup_scale = 1.2       # More aggressive difficulty scaling

Project Structure

alien-invasion/
├── alien_invasion.py       # Main game loop and controller
├── ship.py                 # Ship sprite class
├── bullet.py               # Bullet sprite class
├── alien.py                # Alien sprite class
├── settings.py             # Game configuration and settings
├── create_alien_image.py   # Script to generate alien sprite
├── images/
│   ├── ship.bmp           # Ship sprite image
│   └── alien.bmp          # Alien sprite image
└── README.md              # This file

How the Game Works

Game Loop

1. Check Events: Handle player input (keyboard)
2. Update: Move ship, bullets, and aliens
3. Detect Collisions: Check for bullet-alien hits, alien-ship hits, and aliens reaching bottom
4. Render: Draw all sprites and UI elements
5. Refresh: Update display at 60 FPS

Scoring

• +10 points for each alien destroyed
• Lives: Start with 3
• Game Over: When you lose all lives

Difficulty Progression

• Each completed level (all aliens destroyed) triggers:
  • Speed increase for aliens
  • Speed increase for bullets (optional)
  • New fleet generated at original positions
• Game continues until all lives are lost

Class Overview

AlineInvasion (Main Game)

Manages the overall game flow, sprite groups, collisions, and game state.

Key Methods:

• run_game() - Main game loop
• _check_events() - Handle user input
• _update_bullets() - Update bullet positions
• _update_aliens() - Update alien positions
• _check_collisions() - Detect all collisions
• _create_fleet() - Generate alien formation
• _ship_hit() - Handle ship collision
• _start_new_level() - Progress to next level

Ship

Player-controlled sprite that fires bullets.

Key Methods:

• update() - Move ship based on input flags
• center_ship() - Reset ship position
• blitme() - Draw ship on screen

Bullet

Projectile fired by the ship.

Key Methods:

• update() - Move bullet upward
• draw_bullet() - Draw bullet on screen

Alien

Enemy sprite in the invading fleet.

Key Methods:

• update() - Move alien horizontally
• check_edges() - Detect screen boundary collision

Settings

Configuration class for all game parameters.

Key Methods:

• increase_difficulty() - Scale up game speed

Tips & Tricks

1. Don't waste bullets - You can only have 3 bullets on screen at once
2. Position matters - Try to intercept aliens early before they descend too far
3. Don't get cornered - Move to the center when large groups approach
4. Each level gets harder - Aliens move faster with each completed level
5. Keyboard response - Game runs at 60 FPS for smooth, responsive controls

Troubleshooting

Game won't start

• Ensure pygame is installed: uv pip list | grep pygame
• Check Python version: python --version (requires 3.7+)

Alien images not loading

• Run python create_alien_image.py to generate the alien sprite
• Ensure images/ directory exists

Game is too slow/fast

• Adjust ship_speed, alien_speed in settings.py
• Modify speedup_scale for difficulty progression

Future Enhancement Ideas

Here are some ideas to expand the game:

• 🎵 Sound Effects - Add explosion and shooting sounds
• 💥 Power-ups - Extra lives, rapid fire, shields
• 🎨 Better Graphics - Improved sprite artwork
• 🎯 Obstacles - Bunkers/shields for strategic gameplay
• 📊 High Scores - Persistent leaderboard
• 🌙 Boss Battles - Special enemy waves with unique patterns
• 🏆 Achievements - Complete challenges for badges

Learning Objectives

This project teaches:

• Object-oriented programming in Python
• Game loop structure and timing
• Sprite management with Pygame
• Collision detection algorithms
• Event-driven programming
• Game state management
• Difficulty scaling mechanics

License

Free to use and modify for educational purposes.

Author

Created as a learning project using Python and Pygame.

---

Enjoy the game! 🚀👽