Code an Angry Birds Game: Learn Game Development by Making a Physics Puzzler

Angry Birds is one of the most popular mobile games of all time, and for good reason. Its simple yet satisfying physics-based puzzle gameplay is easy to learn but challenging to master. As it turns out, the core mechanics of Angry Birds are also a great way to learn fundamental game development concepts.

In this article, we‘ll explore how you can code your own Angry Birds-style game from scratch. We‘ll use the Lua programming language and the LÖVE 2D game framework, but the principles we‘ll cover can be applied to virtually any language or engine. By the end, you‘ll have a solid understanding of the key components that make an Angry Birds game tick.

Why Angry Birds is a Great Game to Learn From

Before we dive into the code, let‘s consider what makes Angry Birds such an ideal game to recreate as a learning exercise:

1. 2D Physics: The core of Angry Birds‘ gameplay revolves around two-dimensional physics simulations. Birds are launched at structures, causing them to collapse realistically. Implementing a simplified physics engine is a great way to learn about concepts like collision detection, forces, and object interactions.

2. Simple Mechanics: At its heart, Angry Birds has just a few primary mechanics: aiming and launching birds with a slingshot, destroying obstacles, and defeating pigs. This simplicity makes it relatively straightforward to implement the game‘s core features.

3. Level Design: Angry Birds‘ puzzle-like levels are designed to challenge players‘ problem-solving and spatial reasoning skills. Recreating this level design system will teach you about game balancing, difficulty curves, and creating engaging challenges for players.

4. Extensibility: Once you have the basic game up and running, there are endless ways to expand upon it. You could add new bird types with special abilities, design complex boss battles, or even generate levels procedurally. This flexibility provides opportunity to practice more advanced game development techniques.

Breaking Down the Game‘s Components

An Angry Birds game can be broken down into several core components, each of which represents a key area of functionality:

1. Bird Launching: The primary means of interacting with the game is aiming and launching birds from a slingshot. This requires calculating the bird‘s trajectory based on the slingshot‘s pullback, and applying an impulse force to send it flying.

2. Physics Engine: To simulate realistic destruction, the game needs a physics engine capable of handling collisions between objects, applying gravity and other forces, and breaking objects apart. Box2D is a popular choice, but simpler physics models can work as well.

3. Level Design: Each level in Angry Birds presents a unique arrangement of obstacles, pigs, and other elements. These levels can either be manually designed or procedurally generated based on predefined rules and constraints.

4. Scoring System: Players earn points by destroying obstacles and defeating pigs. The game must track the player‘s current score, as well as their high score across multiple levels or play sessions.

5. Sounds and Effects: Audio and visual effects like explosions, breaking glass, and squawking pigs help sell the game‘s cartoon-like destruction. While not strictly necessary, these little touches add a lot to the overall experience.

By focusing on each of these components in turn, you can create a functional Angry Birds game without getting overwhelmed by the project‘s scope.

Coding an Angry Birds Clone

Now that we have a high-level understanding of the game‘s components, let‘s walk through the actual process of coding a simple Angry Birds clone using Lua and LÖVE 2D. We‘ll assume a basic familiarity with programming concepts, but will explain the specific techniques as we go.

1. Setting Up the Game Loop

The first step is to set up our game loop, which will continuously update and render our game world. In LÖVE 2D, this is done by defining `love.load`, `love.update`, and `love.draw` functions:

function love.load()
  -- Initialize game state
end

function love.update(dt)
  -- Update physics, game logic
end

function love.draw()
  -- Render game objects
end

2. Initializing the Physics World

Next, we need to initialize our physics engine. For this example, we‘ll use a simple custom engine, but you could easily swap in Box2D or another third-party solution. Our basic physics world will just need to track a list of objects and simulate their positions over time:

-- Initialize physics world
physics = {
  gravity = 9.8,
  objects = {}
}

function physics:update(dt)
  -- Update object positions based on velocity 
  for _, object in ipairs(self.objects) do
    object.velocity.y = object.velocity.y + self.gravity * dt
    object.position.x = object.position.x + object.velocity.x * dt
    object.position.y = object.position.y + object.velocity.y * dt
  end
end

3. Creating Game Objects

With our physics world in place, we can start defining the actual game objects. We‘ll need birds, pigs, and obstacles (like wood blocks or stone slabs). Each object will have properties like position, velocity, and dimensions.

-- Bird object
bird = {
  position = vec2(0, 0), 
  velocity = vec2(0, 0),
  radius = 20
}

-- Pig object  
pig = {
  position = vec2(100, 100),
  velocity = vec2(0, 0), 
  width = 40,
  height = 40  
}

-- Add to physics world
table.insert(physics.objects, bird)  
table.insert(physics.objects, pig)

4. Implementing Slingshot Controls

To launch our bird, we need to implement controls for aiming and firing the slingshot. We can do this by tracking touch or mouse input, calculating the pullback vector, and applying an impulse force when released.

-- Track if bird is loaded in slingshot
local birdLoaded = true

function love.mousepressed(x, y, button)
  if button == 1 and birdLoaded then
    -- Start tracking pullback    
    pullbackStart = vec2(x, y)
    pulling = true
  end
end

function love.mousereleased(x, y, button) 
  if button == 1 and pulling then
    -- Launch bird
    local pullbackEnd = vec2(x, y)
    local pullbackVector = pullbackEnd - pullbackStart
    bird.velocity = pullbackVector * 10
    birdLoaded = false
    pulling = false
  end
end

5. Setting Up Levels

Each level will consist of a different arrangement of pigs and obstacles. For now, we can hard-code these level designs in our code, but later you might generate them procedurally or load them from files.

-- Define level data
local levels = {
  {
    pigs = {
      vec2(100, 100), 
      vec2(200, 100)
    },
    blocks = {
      { position = vec2(120, 150), width = 100, height = 20 },
      { position = vec2(180, 200), width = 100, height = 20 }  
    }
  },
  -- Additional levels...
}  

-- Load objects for current level
function loadLevel(levelIndex)
  local level = levels[levelIndex]

  for _, pigPos in ipairs(level.pigs) do
    table.insert(physics.objects, {
      position = pigPos, 
      width = 40,
      height = 40 
    })
  end

  for _, block in ipairs(level.blocks) do
    table.insert(physics.objects, block)
  end
end

6. Detecting Collisions

To determine if our bird has hit any pigs or blocks, we need to implement collision detection. A simple axis-aligned bounding box (AABB) check will suffice for this example:

-- AABB collision detection 
function isColliding(a, b)
  return a.position.x < b.position.x + b.width
     and a.position.x + a.width > b.position.x
     and a.position.y < b.position.y + b.height
     and a.position.y + a.height > b.position.y   
end

-- Check for collisions between bird and other objects
function checkCollisions()
  for i = #physics.objects, 1, -1 do
    local object = physics.objects[i]
    if object ~= bird and isColliding(bird, object) then
      if object.type == "pig" then
        -- Destroy pig
        table.remove(physics.objects, i)
        score = score + 100
      else 
        -- Destroy block  
        table.remove(physics.objects, i)
        score = score + 50
      end
    end
  end
end

7. Resetting Levels

After our bird collides with an object or leaves the screen, we‘ll need to reset the level. If the player has destroyed all the pigs, we can advance to the next level.

function resetLevel()
  -- Remove all objects except bird
  physics.objects = { bird }

  -- Reset bird position and velocity
  bird.position = vec2(0, 0)
  bird.velocity = vec2(0, 0)

  -- Reload current level   
  loadLevel(currentLevel)
  birdLoaded = true
end

function advanceLevel()
  currentLevel = currentLevel + 1
  resetLevel()  
end

-- Check for level completion  
function love.update(dt)
  physics:update(dt)
  checkCollisions()

  if birdLoaded == false then
    local pigsRemaining = false

    for _, object in ipairs(physics.objects) do
      if object.type == "pig" then
        pigsRemaining = true
        break
      end      
    end

    if not pigsRemaining then
      advanceLevel()
    elseif bird.position.y > love.graphics.getHeight() then  
      resetLevel()
    end
  end
end  

8. Finishing Touches

With the core gameplay in place, you can start adding some extra polish:

• Draw sprites for each game object
• Add sound effects and music
• Display the current score and level number
• Implement a game over screen when all levels are completed

You can also expand the gameplay with new features:

• Different bird types with special abilities (like splitting or bombing)
• TNT boxes and other explosive obstacles
• Multi-phase levels with boss pigs

The beauty of a game like Angry Birds is that it offers a solid foundation to build upon and experiment with your own ideas.

Key Takeaways

Coding an Angry Birds game is a fun way to learn essential game development techniques that are applicable to many other types of projects:

• Physics simulations: Angry Birds‘ destructible environments are a great showcase for 2D physics. Learning how to implement a physics engine, detect collisions, and resolve object interactions is a key skill for many game genres.

• Game state management: Even a simple game like Angry Birds requires careful tracking of game state, like the current score, level number, and bird spawn states. Figuring out how to efficiently store and update this data is crucial for making more complex games.

• Object-oriented design: Angry Birds provides a natural use case for object-oriented programming, with its bird, pig, and obstacle classes. Structuring your game entities as objects with specific properties and behaviors is an essential pattern to master.

• Level design: Creating engaging, balanced levels is one of the trickiest parts of game design. Angry Birds‘ compact puzzle-like levels are an approachable way to learn about pacing, difficulty curves, and teaching mechanics through play.

By breaking down Angry Birds into its core components and mechanics, you can create a functional clone while learning valuable programming concepts along the way. So why not give it a shot? With some practice and creativity, you might just come up with the next addictive mobile game!