As a coding teacher with over 10 years of experience, one of the most frequent game requests I get from students is to build something like Angry Birds. The hugely popular mobile game makes physics-based projectile motion accessible and fun.
In this comprehensive guide, I‘ll walk you through building a basic Angry Birds clone from scratch using Lua and the LÖVE2D framework. Along the way, you‘ll learn key game development concepts that can be applied to crafting all kinds of 2D games.
Understanding Angry Birds Gameplay
Let‘s briefly examine what gives Angry Birds its widespread appeal. Each level features:
- Bird characters with different abilities
- Intricate structures made of wood, ice and stone
- Using a slingshot to launch birds at the structures
- Scoring points by damaging or demolishing structures
- Lighthearted, humorous visual style
At its heart, it utilizes principles of trajectory projection, gravity, collision detection and basic game physics to create fun and challenging levels. Now we‘ll break down how to code these elements!
Getting Set Up with LÖVE2D
LÖVE2D is a free, open-source framework for building 2D games in Lua. Some key advantages:
- Handles graphics, sound and input
- Built-in physics module
- Good documentation and community
- Wide device support
We‘ll use LÖVE because of its simplicity for prototyping ideas quickly. Download it from www.love2d.org and create a folder for your project.
Inside the main.lua file, we initialize LÖVE:
function love.load() -- setup code here endfunction love.update(dt)-- game logic code end
function love.draw()-- render gameplay
end
This splits up the key tasks our game loop needs to handle. Now let‘s start populating each section!
Drawing the Game World
We first want to create our game screen by drawing some basic visual elements:
- Green grassy area for the structures to inhabit
- Blue sky backdrop
- Slingshot at the bottom to hurl birds from
In love.draw(), we can leverage LÖVE‘s graphics APIs:
function love.draw() love.graphics.setColor(0.5, 0.8, 0.5) love.graphics.rectangle("fill", 0, 120, 400, 200)love.graphics.setColor(0, 0, 1)love.graphics.rectangle("fill", 0, 0, 400, 120)love.graphics.setColor(1, 1, 0)love.graphics.rectangle("fill", 10, 310, 80, 20)
end
This will render basic colored shapes for the ground, sky, and slingshot. Later we can refine with images and textures.
Coding Angry Bird Physics
Now for the fun part – getting our angry bird to act like a projectile! We‘ll break it down into steps:
- Create bird sprite
- Initialize variables for gravity, velocity
- Apply trajectory math each frame
- Detect and handle collisions
Let‘s chunk this out piece by piece, starting with creating our main bird character.
Implementing the Bird Sprite
We can draw a basic red circle for our angry bird:
local bird = {}bird.x = 50bird.y = 200 bird.width = 20bird.height = 20function love.draw()love.graphics.setColor(1, 0, 0)love.graphics.circle("fill", bird.x, bird.y, bird.width)end
Later on we can texture this with an actual art asset! We‘ll build behaviors next.
Coding Gravity and Projectile Motion
The core mechanic is launching this bird with physics. Let‘s code gravity first:
local gravity = 10function love.update(dt)bird.y = bird.y + gravity * dtend
This will make our bird object fall downwards every frame! Next we add horizontal velocity:
local speed = 140local vx = speedfunction love.update(dt)bird.x = bird.x + vx dtbird.y = bird.y + gravity dt end
By separating X and Y velocity, we can model projectile motion! We increment the bird‘s position each frame based on these accelerations.
Improving Trajectory Physics
To really sell the angry birds arc, let‘s make our velocity vectors more realistic. We‘ll increase vertical speed over time:
local vy = 0local maxHeight = 100function love.update(dt)vx = vx * 0.99
vy = vy + gravity * dtif bird.y >= startY + maxHeight then vy = vy * 0.8 endbird.x = bird.x + vx * dtbird.y = bird.y + vy * dt
end
Here we gradually slow the horizontal speed, while accelerating vertical speed up and down to arc more. Tweak constants until it looks right!
There are many more refinements we can add, but this core will get our bird‘s motion feeling right! Next up is handling collisions…
Detecting and Handling Collisions
What fun is launching angry birds if they don‘t get to smash into things? Let‘s explore how to implement collisions.
We need to:
- Create destructible objects for the birds to intersect
- Continuously check for overlaps each frame
- Apply damage and physics impulses on contact
Let‘s build breakable stone columns our bird can knock down!
Coding Breakable Columns
We‘ll make columns with a health value that depletes when hit by birds:
local columns = {}for x = 50, 350, 60 dotable.insert(columns, {x = x,y = 160,width = 40,height = 100,health = 15})end
function love.update(dt)-- check for collisionsend
function love.draw()for k, col in pairs(columns) dolove.graphics.setColor(0.3, 0.3, 0.3) love.graphics.rectangle("fill", col.x, col.y, col.width, col.height)endend
This generates a set of columns spaced horizontally across our level. Next we can make them react to collisions.
Checking for Intersections
Each frame, we need to see if any columns intersect with the bird, then apply damage:
function checkCollision(a, b) -- Check intersect logicendfunction love.update(dt)for k, col in pairs(columns) do
if checkCollision(bird, col) thencol.health = col.health - 1endend endThe separate checkCollision function handles detecting overlap between shapes. If health reaches 0, we can remove that column entirely.
Applying Collision Physics
To sell the impacts, we also want physical reactions from the collision:
function checkCollision(a, b) -- Physics impact logicif bird.x + bird.width > b.x and b.health > 0 thenvx = -vx * 0.5bird.x = b.x - bird.width endend
Here when columns are hit, we reverse and dampen velocity on the x-axis. We also constrain position to stop interpenetration. Similar logic can act on the column health and position.
With these pieces, our basic angry birds game is really starting to take shape! We still need to implement scoring, levels and other features to polish it off.
Expanding Your Angry Birds Game
Even with basic physics and collisions implemented, there are still plenty of improvements we can make:
- More diverse and complex levels
- Slingshot mechanic for aiming and firing birds
- Damage scoring system and UI
- Animations and juicy feedback for events
- More birds like Blues and Yellows!
By iterating on the foundation we‘ve built so far, you can continue expanding the scope and fun. Try tweaking and building on top of the example code shown here.
The core techniques showcased will assist you in coding all kinds of 2D physics games beyond just Angry Birds. Options are endless when you understand principles like trajectories and spatial reasoning.
I hope this guide has shown how achievable something like Angry Birds can be, while demystifying many key game dev concepts along the way. Let me know if you have any other questions!