Question: How do you use physics in Love2D?

Answer

Love2D, also known as LÖVE, supports physics through a built-in module called love.physics. This module is essentially a Lua wrapper around the Box2D physics engine. To utilize physics in your Love2D game, you must initialize a world and then create bodies, shapes, and fixtures within that world.

Here's an example of how to set up a simple physics world with a falling rectangle:

function love.load()
    -- Load the love.physics module
    love.physics.setMeter(64) -- sets the scale for the physics world
    world = love.physics.newWorld(0, 9.81*64, true) -- creates a new physics world with gravity

    -- Create the ground body
    objects = {}
    objects.ground = {}
    objects.ground.body = love.physics.newBody(world, love.graphics.getWidth() / 2, love.graphics.getHeight() - 50, "static")
    objects.ground.shape = love.physics.newRectangleShape(650, 50)
    objects.ground.fixture = love.physics.newFixture(objects.ground.body, objects.ground.shape)

    -- Create a falling body
    objects.block = {}
    objects.block.body = love.physics.newBody(world, love.graphics.getWidth() / 2, love.graphics.getHeight() / 2, "dynamic")
    objects.block.shape = love.physics.newRectangleShape(0, 0, 50, 50)
    objects.block.fixture = love.physics.newFixture(objects.block.body, objects.block.shape, 2) -- The density (last argument) affects the mass
end

function love.update(dt)
    world:update(dt) -- updates the physics world
end

function love.draw()
    -- Draw the ground
    love.graphics.setColor(0.28, 0.63, 0.05)
    love.graphics.polygon("fill", objects.ground.body:getWorldPoints(objects.ground.shape:getPoints()))

    -- Draw the block
    love.graphics.setColor(0.76, 0.18, 0.05)
    love.graphics.polygon("fill", objects.block.body:getWorldPoints(objects.block.shape:getPoints()))
end

Key Points:

1. Initialize the Physics World: Use love.physics.newWorld to create a new world.
2. Set the Scale: love.physics.setMeter defines the size of a meter in the world which helps in scaling the physics simulation.
3. Create Bodies: Bodies are entities that have mass and can interact in the physics simulation (love.physics.newBody).
4. Attach Shapes: Shapes define the form of the physics entity, used for collision detection (love.physics.newRectangleShape for rectangles).
5. Create Fixtures: A fixture binds a shape to a body and adds material properties like density (love.physics.newFixture).
6. Update the World: The world needs to be updated in the love.update callback, typically using the delta time (dt) since the last frame.
7. Draw the Objects: In love.draw, you visually represent the physics entities, using their physical properties to dictate position and rotation.

By adding more bodies, shapes, and joints, you can create complex physics simulations in your Love2D games.