Simple spaceship scroller game demo in Lua with the Love game engine

spacescroller.lua

function love.load()
  config = {
    initial_x       = 200,
    initial_y       = 400,
    step            = 500,
    numStars        = 100,
    starSpeedFactor = 1
  }
  
  spaceship = {
    image         = love.graphics.newImage("images/love-ball.png"),
    x             = config.initial_x,
    y             = config.initial_y,
    isBoosted     = false,
    boostFactor   = 4,
    boostDuration = 2,
    timeBoosted   = 0
  }
  
  star = love.graphics.newImage("images/star.png")
  stars = {}
  love.graphics.setColorMode("modulate")
  scrollerHeight = 30
  letterSize = 21
  angle = {}
  x = {}
  initStars()
end

function love.update(dt)
  if spaceship.isBoosted then
    spaceship.timeBoosted = spaceship.timeBoosted + dt
    if spaceship.timeBoosted >= spaceship.boostDuration then
      spaceship.isBoosted = false
      config.starSpeedFactor = 1
    end
  end
  
  if love.keyboard.isDown("left") and (spaceship.x - config.step * dt) >= 0 then
    spaceship.x = spaceship.x - config.step * dt
  end
  
  if love.keyboard.isDown("right") and (spaceship.x + config.step * dt) < 740 then
    spaceship.x = spaceship.x + config.step * dt
  end
  
  if love.keyboard.isDown("up") and (spaceship.y - config.step * dt) >= 0 then
    spaceship.y = spaceship.y - config.step * dt
  end
  
  if love.keyboard.isDown("down") and (spaceship.y + config.step * dt) < 540  then
    spaceship.y = spaceship.y + config.step * dt
  end
  
  for i = 1,config.numStars do
    stars[i].x = stars[i].x - stars[i].speed * config.starSpeedFactor * dt
    if stars[i].x < -20 then
      stars[i].x = math.random(830, 900)
      stars[i].y = math.random(1,600)
    end
    angle[i] = angle[i] + math.pi/1.5 * dt;   
    x[i] = x[i] - letterSize*3*dt
    if x[config.numStars-1] < -letterSize*2 then
      initStars()
    end
  end
end

function love.keypressed(k)
  if k == ' ' and not spaceship.isBoosted then
    config.starSpeedFactor  = spaceship.boostFactor
    spaceship.isBoosted     = true
    spaceship.timeBoosted   = 0
  end
end

function love.draw()
  for i = 1,config.numStars do  
    love.graphics.setColor(255 - stars[i].speed,255 - stars[i].speed/2,150,stars[i].speed*0.9);   
    love.graphics.draw(star, stars[i].x, stars[i].y, 0, stars[i].speed/255 + 0.55)
  end
  
  love.graphics.setColor(255, 255, 255)
  love.graphics.draw(spaceship.image, spaceship.x, spaceship.y)
  love.graphics.print("spaceship.timeBoosted: " .. spaceship.timeBoosted, 10, 20)
end

function initStars()
  local w = 800
  for i = 1,config.numStars do
    table.insert(stars, {x = math.random(1,800), y = math.random(1,600), speed = math.random(2,255)})
    angle[i] = i*6
    x[i] = w+i*letterSize
  end
end