"Marmalade Quick" lua-based simple Ping Pong game

main.lua

--[[
Provided by Tim Closs see https://devnet.madewithmarmalade.com/questions/3701/kinematic-bodies-in-marmalade-quick.html

Ping pong game.
Drag the bats up and down, and attempt to keep the ball in play.
The bats and ball are physics "sensor" objects, so generate collision
events but no physical responses.
--]]
 
local dw = director.displayWidth
local dh = director.displayHeight
 
local batW = 20
local batH = 80
local ballSpeed = 3
 
physics:setGravity(0, 0)
 
-- Touch listener to drag bats
function dragBat(event)
    local bat = event.target
    if event.phase == "began" then
       bat.yTouchLast = event.y
    elseif event.phase == "moved" then
       bat.yVel = event.y - bat.yTouchLast;
        bat.yTouchLast = event.y
       bat.y = bat.y + bat.yVel
    end
end
 
-- Collision listener
function hit(event)
    if event.phase == "began" then
        local bat, ball
        if event.nodeA.radius then
            bat = event.nodeB
            ball = event.nodeA
        else
            ball = event.nodeB
            bat = event.nodeA
        end
        if ball.vx < 0 then
           ball.x = bat.x + (bat.w + ball.w)/2
        else
           ball.x = bat.x - (bat.w + ball.w)/2
        end
        ball.vx = -ball.vx
        ball.vy = bat.yVel or 0
        return true
    end
end
 
-- Create left bat
local batL = director:createRectangle( {
    x=batW*3/2, y=dh/2, w=batW, h=batH, name="batL",
    color=color.darkRed, strokeColor=color.red,
    } )
physics:addNode(batL, {isSensor=true})
batL:addEventListener("touch", dragBat)
batL:addEventListener("collision", hit)
 
-- Create right bat
local batR = director:createRectangle( {
    x=dw-batW*3/2, y=dh/2, w=batW, h=batH, name="batR",
    color=color.darkGreen, strokeColor=color.green,
    } )
physics:addNode(batR, {isSensor=true})
batR:addEventListener("touch", dragBat)
batR:addEventListener("collision", hit)
 
-- Create ball
local ball = director:createCircle( {
    x=dw/2, y=dh/2, radius=batW/2, name="ball",
    } )
physics:addNode(ball, {isSensor=true, radius=ball.radius})
ball:addEventListener("collision", hit)
ball.inTimer = 2 -- count down from 2 seconds before starting ball
 
-- Update for ball
function updateBall(event)
    -- Are we simply waiting for the ball to appear again?
    if ball.inTimer > 0 then
        ball.inTimer = ball.inTimer - system.deltaTime
        if ball.inTimer < 0 then
            ball.inTimer = 0
            ball.isVisible = true
        end
    end
 
    -- Bounce off top/bottom of display?
    if ball.y < ball.radius then
       ball.y = ball.radius
       ball.vy = -ball.vy
    elseif ball.y > dh - ball.radius then
       ball.y = dh - ball.radius
       ball.vy = -ball.vy
    end
 
    -- Move ball: add velocity to position
    ball.x = ball.x + ball.vx
    ball.y = ball.y + ball.vy
 
    -- Ball out of play (off left/right)? If so, re-center
    if ball.x < 0 or ball.x > dw then
       ball.x = dw/2
       ball.y = dh/2
       ball.vx = ballSpeed
       ball.vy = 0
        ball.inTimer = 2 -- count down from 2 seconds before starting ball again
        ball.isVisible = false
    end
end
system:addEventListener("update", updateBall)
 
-- Add our own velocity properties to the ball sprite object
ball.vx = ballSpeed
ball.vy = 0