Corona SDK Touch Joint Example

require "physics"
physics.start()
physics.setGravity(0, 9.8)
physics.setDrawMode("hybrid")

stage = display.getCurrentStage()

function getWall(x, y, width, height)
    local wall = display.newRect( x, y, width, height)
    wall:setFillColor( 255, 0, 0, 100)
    physics.addBody(wall, "static", { friction=0.5, bounce=0.0, density=2 } )
    return wall
end

function getBall(x, y, radius, type, props)
    if props == nil then
        props = {density=0.3, friction=0.3, bounce=0.3}
    end
    local ball = display.newCircle(x, y, radius)
    ball:setFillColor(0, 255, 0)
    physics.addBody(ball, props)
    return ball
end

floor = getWall(0, 460, 320, 20)
leftWall = getWall(0, 0, 20, 500)
rightWall = getWall(320, 0, 20, 500)
roof = getWall(0, 0, 460, 20)

ball1 = getBall(100, 100, 10, {density=0.3, friction=0.3, bounce=2})
ball2 = getBall(200, 150, 10, {density=0.3, friction=0.3, bounce=2})

touchJoint = nil

function onTouch(event)
    print(tostring(system.getTimer()) .. " phase: ", event.phase)
    if event.phase == "began" then
        dragging = true
        stage:setFocus(ball1)
        ball1.bodyType = "kinetic"
        if touchJoint then
            touchJoint:removeSelf()
        end
        touchJoint = physics.newJoint( "touch", ball1, event.x, event.y )
        --touchJoint.maxForce = 10000000
        touchJoint.frequency = 0.5
        touchJoint.dampingRatio = 0
        return true
    elseif event.phase == "moved" then
        if dragging == false then return false end
        touchJoint:setTarget(event.x, event.y)
        return true
    elseif event.phase == "ended" or event.phase == "cancelled" then
        if dragging == true then
            dragging = false
            ball1.bodyType = "dynamic"
            touchJoint:removeSelf()
            touchJoint = nil
            return true
        else
            return false
        end
    end
end


Runtime:addEventListener("touch", onTouch)