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Overview

Space Birds uses a state machine with three primary states to manage game flow. Each state has distinct visuals, controls, and behaviors.

State Machine

The game uses the GameState enum with three states:
  • MENU: Starting point and main menu
  • PLAYING: Active gameplay
  • GAME_OVER: End screen with final score

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State Diagram

The game starts in MENU state when launched and cycles through these states until the application is closed.

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Description

The initial state where players can start a new game. This is the default state when the game first launches or after returning from GAME_OVER.

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Visual Elements

ElementDescription
BackgroundSpace logo image (space.jpg) filling entire screen
Text Line 1”Pulsa ESPACIO o ENTER para comenzar”
Text Line 2”Controles: FLECHAS para mover, ESPACIO para disparar”
Text Line 3”ENTER para ver puntuación durante el juego”
MusicAngry Birds theme (angry-birds.mp3) looping at 50% volume

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Available Controls

SPACE Key

Starts the game → PLAYING

ENTER Key

Starts the game → PLAYING

Touch Screen

Starts the game → PLAYING

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State Initialization

When entering MENU state:
  • Background menu music starts playing
  • Game logo is displayed
  • Control instructions are shown
  • Player object exists but is not active
The MENU state does not update obstacles or process gameplay logic. It’s purely a waiting state.

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PLAYING State

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Description

The active gameplay state where the player controls the bird, shoots bullets, avoids pigs, and accumulates score.

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Visual Elements

ElementLocationDescription
BackgroundFull screenNight sky image (noche.jpg)
Player BirdBottom centerRed bird (64×64px) that moves based on input
PigsFalling from topEnemy pigs (62×48px) spawning every 0.5s
BulletsMoving upwardRed projectiles (10×20px) from player
TimerTop-right”Tiempo: Xs” showing survival time
Kill CountTop-right”Asteroides: X” showing pigs destroyed
ScoreTop-right”Puntos: X” showing current total
StatusCenter-bottom”Jugando…” in red text
InstructionsTop-leftESC and ENTER key reminders
Flash EffectFull screenWhite flash when shooting (0.1s duration)

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Active Systems

Movement System

Processes keyboard, touch, and mouse input for player movement within screen boundaries

Shooting System

Handles bullet creation with 0.3s cooldown, bullet movement, and removal when off-screen

Spawn System

Generates new pigs every 0.5 seconds at random horizontal positions

Collision System

Detects bullet-pig and bird-pig collisions

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Available Controls

InputAction
Arrow KeysMove bird (↑↓←→)
SPACEShoot bullet
Right ClickShoot bullet (alternative)
TouchMove bird toward touch position
ENTERShow score screen overlay
ESCQuit to game over

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State Updates

Every frame during PLAYING:
  1. Delta time is calculated
  2. Game time increases
  3. Spawn timer increases (pigs spawn at 0.5s intervals)
  4. Player updates (position, bullets, cooldown)
  5. Obstacles update (position, removal if off-screen)
  6. Collision detection runs for bullets and bird
  7. Flash effect timer decreases if active

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Music

Battle music (battle.mp3) loops at 150% volume during PLAYING state.
The music pauses when you open the score screen with ENTER and resumes when you close it.

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GAME_OVER State

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Description

The end state displayed when the player dies (collision) or quits (ESC). Shows final score and allows return to menu.

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Visual Elements

ElementDescription
BackgroundRed screen (solid red fill)
Title Text”GAME OVER” in yellow (center-top)
Score Text”Puntuación final: X” in yellow (center)
Instruction”Pulsa ENTER para volver al menú” (center-bottom)

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Score Calculation

When transitioning to GAME_OVER, the final score is calculated: 
int tiempoPuntos = (int) gameTime;           // 1 point per second
int asteroidesPuntos = asteroidsDestroyed * 10; // 10 points per kill
score = tiempoPuntos + asteroidesPuntos;
The score is locked in at the moment of game over and cannot change in this state.

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Available Controls

ENTER Key Only

Pressing ENTER returns to MENU state
Touch and other inputs are disabled in GAME_OVER state. Only ENTER works.

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State Cleanup

The GAME_OVER state does not perform cleanup. When ENTER is pressed and the game returns to MENU, the cleanup happens:
  • All obstacles are cleared from memory
  • Game music stops
  • Menu music starts
  • Score resets to 0
  • Kill counter resets to 0
  • Game time resets to 0
  • Spawn timer resets to 0

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State Transitions

Triggers: SPACE key, ENTER key, or Touch input Actions:
  1. Menu music pauses
  2. Battle music starts
  3. Player activates (engine sound plays)
  4. Game time resets to 0
  5. Spawn timer resets to 0
  6. All obstacles cleared
  7. State changes to PLAYING
This transition prepares a fresh game session with clean counters and cleared obstacles.

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PLAYING → GAME_OVER

Triggers:
  • Player collision with pig (automatic)
  • ESC key pressed (manual quit)
Actions:
  1. Final score calculated
  2. State changes to GAME_OVER
  3. Game music continues playing until ENTER pressed
  4. Red screen displayed
  5. Score shown
When a collision occurs, the game immediately transitions to GAME_OVER without any “death animation” or delay.

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GAME_OVER → MENU

Trigger: ENTER key Actions:
  1. Game music stops
  2. Menu music starts
  3. All obstacles cleared
  4. Score resets to 0
  5. Kill counter resets to 0
  6. Game time resets to 0
  7. Spawn timer resets to 0
  8. State changes to MENU
This transition performs a complete game reset, so you start fresh when entering PLAYING again.

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State Management Implementation

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State Change Mechanism

The game uses a two-variable system: 
private GameState gameState;      // Current active state
private GameState nextGameState;  // Pending state for next frame
private boolean gameStateChanged; // Flag indicating transition pending

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Transition Process

1

Trigger Detected

When a state transition is triggered (button press, collision), the game sets:
  • nextGameState to the target state
  • gameStateChanged to true
2

Frame Completes

Current frame finishes rendering with the old state
3

State Change Processed

At the end of the render cycle, if gameStateChanged is true:
  • Cleanup/initialization code runs
  • gameState = nextGameState
  • gameStateChanged = false
4

Next Frame Begins

Next frame renders with the new state
This deferred transition system prevents state changes mid-frame, which could cause rendering glitches or logic errors.

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Special State Features

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Score Screen Overlay

While in PLAYING state, pressing ENTER shows a score screen overlay:
  • Does NOT change the game state
  • Pauses background music
  • Shows detailed score information
  • Can be dismissed to resume
  • Gameplay continues in background (not paused)
This is not a true “pause” - pigs keep spawning and moving while the score screen is shown!

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Pause State

The game has a gamePaused boolean variable, but it’s only used for the score screen overlay feature: 
private boolean gamePaused;
This does NOT implement true game pausing - it only tracks UI state.
There is no built-in pause function that stops gameplay. Pressing ESC immediately ends the game.

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State-Specific Music

StateMusicVolumeLooping
MENUangry-birds.mp350%Yes
PLAYINGbattle.mp3150%Yes
GAME_OVER(continues previous)--
The battle music volume is set to 150% for an intense gameplay atmosphere. The menu music is gentler at 50%.

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