Contact

Contacts are objects created to manage collisions in worlds.

The lifetimes of Contacts are short. When you receive them in callbacks, they may be destroyed immediately after the callback returns. Cache their values instead of storing Contacts directly.

Functions

Contact:getChildren	Gets the child indices of the shapes of the two colliding fixtures.	0.9.0
Contact:getFixtures	Gets the two Fixtures that hold the shapes that are in contact.	0.9.2
Contact:getFriction	Get the friction between two shapes that are in contact.
Contact:getNormal	Get the normal vector between two shapes that are in contact.
Contact:getPosition	Get the location of the contact point between two shapes.		0.8.0
Contact:getPositions	Returns the contact points of the two colliding fixtures.	0.8.0
Contact:getRestitution	Get the restitution between two shapes that are in contact.
Contact:getSeparation	Get the separation between two shapes that are in contact.		0.8.0
Contact:getVelocity	Get the linear impact velocity of a contact.		0.8.0
Contact:isEnabled	Returns whether the contact is enabled.	0.8.0
Contact:isTouching	Returns whether the two colliding fixtures are touching each other.	0.8.0
Contact:resetFriction	Resets the contact friction to the mixture value of both fixtures.	0.8.0
Contact:resetRestitution	Resets the contact restitution to the mixture value of both fixtures.	0.8.0
Contact:setEnabled	Enables or disables the contact.	0.8.0
Contact:setFriction	Sets the contact friction.	0.8.0
Contact:setRestitution	Sets the contact restitution.	0.8.0
Object:release	Immediately destroys the object's Lua reference.	11.0
Object:type	Gets the type of the object as a string.
Object:typeOf	Checks whether an object is of a certain type.
World:setCallbacks	Sets functions to be called when shapes collide.	0.8.0

Supertypes

• Object

See Also

• World:setCallbacks
• World:getContacts
• love.physics

Examples

-- Demonstration of correct use of Contacts to avoid "Attempt to use destroyed contact."
-- Most relevant parts are physics.collisionOnEnter, love.update, love.draw.

local screen = {
    x = 500,
    y = 500,
}
local color = {
    blue = {0.23, 0.25, 0.59, 1},
    purple = {0.25, 0.09, 0.28, 1},
    white = {0.89, 0.91, 0.90, 1},
}

local physics = {
    normals = {},
}

-- Source: https://www.love2d.org/forums/viewtopic.php?p=17018&sid=5c8509cf6b97e3ce5aab1bc49e85acc5#p17018
local function draw_arrow(x1, y1, x2, y2)
    local head_length = 10
    local head_angle = math.pi * 0.2
    love.graphics.line(x1, y1, x2, y2)
    local a = math.atan2(y1 - y2, x1 - x2)
    love.graphics.polygon('fill', x2, y2, x2 + head_length * math.cos(a + head_angle), y2 + head_length * math.sin(a + head_angle), x2 + head_length * math.cos(a - head_angle), y2 + head_length * math.sin(a - head_angle))
end


function physics.collisionOnEnter(fixture_a, fixture_b, contact)
    local dx,dy = contact:getNormal()
    dx = dx * 30
    dy = dy * 30
    local point = {contact:getPositions()}
    for i=1,#point,2 do
        local x,y = point[i], point[i+1]
        -- Cache the values inside the contacts because they're not guaranteed
        -- to be valid later in the frame.
        table.insert(physics.normals, {x,y, x+dx, y+dy})
    end

    -- do not use contact after this function returns
end

function love.load()
    love.physics.setMeter(64)
    local can_bodies_sleep = true
    physics.world = love.physics.newWorld(0, 9.8, can_bodies_sleep)
    physics.world:setCallbacks(physics.collisionOnEnter)

    physics.geo = {}
    for y=0,1 do
        local side = {}
        side.body = love.physics.newBody(physics.world, screen.x/2, screen.y * y)
        side.shape = love.physics.newRectangleShape(screen.x, 50)
        side.fixture = love.physics.newFixture(side.body, side.shape)
        table.insert(physics.geo, side)
    end
    for x=0,1 do
        local side = {}
        side.body = love.physics.newBody(physics.world, screen.x * x, screen.y/2)
        side.shape = love.physics.newRectangleShape(50, screen.y)
        side.fixture = love.physics.newFixture(side.body, side.shape)
        table.insert(physics.geo, side)
    end

    physics.bouncers = {}
    for y=50,screen.y-50,50 do
        for x=50,screen.x-100,50 do
            local ball = {}
            ball.body = love.physics.newBody(physics.world, x, y, "dynamic")
            ball.shape = love.physics.newCircleShape(20)
            ball.fixture = love.physics.newFixture(ball.body, ball.shape, 1)
            ball.fixture:setRestitution(0.9)
            ball.body:setMass(50)
            ball.body:setLinearVelocity(100, 10)
            table.insert(physics.bouncers, ball)
        end
    end

    love.graphics.setBackgroundColor(color.blue)
    love.window.setMode(screen.x, screen.y)
end

function love.update(dt)
    -- Updating the world will trigger collisionOnEnter
    physics.world:update(dt)

    if love.keyboard.isDown("space") then
        for _,ball in ipairs(physics.bouncers) do
            ball.body:applyLinearImpulse(0, 1000)
        end
    elseif love.keyboard.isDown("escape") then
        love.event.quit()
    end
end

function love.draw()
    love.graphics.setColor(color.purple)
    for i,side in ipairs(physics.geo) do
        love.graphics.polygon("fill", side.body:getWorldPoints(side.shape:getPoints()))
    end
    for i,ball in ipairs(physics.bouncers) do
        love.graphics.circle("fill", ball.body:getX(), ball.body:getY(), ball.shape:getRadius())
    end

    love.graphics.setColor(color.white)
    love.graphics.printf("smoosh balls with space", 5,5, 200, "left")
    love.graphics.printf(string.format("%i contacts", #physics.normals), screen.x-100,5, 100, "right")
    love.graphics.printf("arrows show contact normals", 5,screen.y-20, 200, "left")

    -- Use our cached normals
    for key,args in pairs(physics.normals) do
        local x1, y1, x2, y2 = unpack(args)
        draw_arrow(x1, y1, x2, y2)
        physics.normals[key] = nil
    end
end

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