Scrolling Shooter from the tutorial “Your First Love2d Game in 200 Lines”

conf.lua

-- Configuration
function love.conf(t)
  t.title         = "Scrolling Shooter"
  t.version       = "0.9.2"
  t.window.width  = 480
  t.window.height = 700

  t.console = true
end

main.lua

debug     = true
player    = { x = 200, y = 610, speed = 150, img = nil }

isAlive = true
score = 0

-- Timers
-- We declare these here so we don't have to edit them multiple places
canShoot = true
canShootTimerMax = 0.2
canShootTimer = canShootTimerMax

-- Image Storage
bulletImg = nil

-- Entity Storage
bullets = {} -- array of current bullets being drawn and updated

--More timers
createEnemyTimerMax = 0.4
createEnemyTimer = createEnemyTimerMax

-- More images
enemyImg = nil -- Like other images we'll pull this in during out love.load function

-- More storage
enemies = {} -- array of current enemies on screen

function love.load(arg)
  player.img = love.graphics.newImage('assets/plane.png')
  bulletImg  = love.graphics.newImage('assets/bullet.png')
  enemyImg   = love.graphics.newImage('assets/enemy.png')
  gunSound   = love.audio.newSource('assets/gun-sound.wav', 'static')
end

function love.update(dt)
  if love.keyboard.isDown('escape') then
    love.event.push('quit')
  end

  if love.keyboard.isDown('left','a') then
    if player.x > 0 then -- binds us to the map
      player.x = player.x - (player.speed*dt)
    end
  elseif love.keyboard.isDown('right','d') then
    if player.x < (love.graphics.getWidth() - player.img:getWidth()) then
      player.x = player.x + (player.speed*dt)
    end
  end

  -- Time out how far apart our shots can be.
  canShootTimer = canShootTimer - (1 * dt)
  if canShootTimer < 0 then
    canShoot = true
  end

  if love.keyboard.isDown(' ', 'rctrl', 'lctrl', 'ctrl') and canShoot then
    -- Create some bullets
    newBullet = { x = player.x + (player.img:getWidth()/2), y = player.y, img = bulletImg }

    table.insert(bullets, newBullet)

    gunSound:play()

    canShoot = false
    canShootTimer = canShootTimerMax
  end

  -- Vertical movement
  if love.keyboard.isDown('up', 'w') then
    if player.y > (love.graphics.getHeight() / 2) then
      player.y = player.y - (player.speed*dt)
    end
  elseif love.keyboard.isDown('down', 's') then
    if player.y < (love.graphics.getHeight() - 55) then
      player.y = player.y + (player.speed*dt)
    end
  end

  -- update the positions of bullets
  for i, bullet in ipairs(bullets) do
    bullet.y = bullet.y - (250 * dt)

    if bullet.y < 0 then -- remove bullets when they pass off the screen
      table.remove(bullets, i)
    end
  end

  -- Time out enemy creation
  createEnemyTimer = createEnemyTimer - (1 * dt)
  if createEnemyTimer < 0 then
    createEnemyTimer = createEnemyTimerMax

    -- Create an enemy
    randomNumber = math.random(80, love.graphics.getWidth() - 80)
    newEnemy = { x = randomNumber, y = -10, img = enemyImg }
    table.insert(enemies, newEnemy)
  end

  -- update the positions of enemies
  for i, enemy in ipairs(enemies) do
    enemy.y = enemy.y + (200 * dt)

    if enemy.y > 700 then -- remove enemies when they pass off the screen
      table.remove(enemies, i)
    end
  end

  -- run our collision detection
  -- Since there will be fewer enemies on screen than bullets we'll loop them first
  -- Also, we need to see if the enemies hit our player
  for i, enemy in ipairs(enemies) do
    for j, bullet in ipairs(bullets) do
      if CheckCollision(enemy.x, enemy.y, enemy.img:getWidth(), enemy.img:getHeight(), bullet.x, bullet.y, bullet.img:getWidth(), bullet.img:getHeight()) then
        table.remove(bullets, j)
        table.remove(enemies, i)
        score = score + 1
      end
    end

    if CheckCollision(enemy.x, enemy.y, enemy.img:getWidth(), enemy.img:getHeight(), player.x, player.y, player.img:getWidth(), player.img:getHeight())
    and isAlive then
      table.remove(enemies, i)
      isAlive = false
    end
  end

  if not isAlive and love.keyboard.isDown('r') then
    -- remove all our bullets and enemies from screen
    bullets = {}
    enemies = {}

    -- reset timers
    canShootTimer = canShootTimerMax
    createEnemyTimer = createEnemyTimerMax

    -- move player back to default position
    player.x = 200
    player.y = 610

    -- reset our game state
    score = 0
    isAlive = true
  end
end

function love.draw(dt)
  for i, bullet in ipairs(bullets) do
    love.graphics.draw(bullet.img, bullet.x, bullet.y)
  end

  for i, enemy in ipairs(enemies) do
    love.graphics.draw(enemy.img, enemy.x, enemy.y)
  end

  if isAlive then
    love.graphics.draw(player.img, player.x, player.y)
  else
    love.graphics.print("Press 'R' to restart", love.graphics:getWidth()/2-50, love.graphics:getHeight()/2-10)
  end
end

-- Collision detection taken function from http://love2d.org/wiki/BoundingBox.lua
-- Returns true if two boxes overlap, false if they don't
-- x1,y1 are the left-top coords of the first box, while w1,h1 are its width and height
-- x2,y2,w2 & h2 are the same, but for the second box
function CheckCollision(x1,y1,w1,h1, x2,y2,w2,h2)
  return x1 < x2+w2 and
         x2 < x1+w1 and
         y1 < y2+h2 and
         y2 < y1+h1
end

Tutorial: http://osmstudios.com/tutorials/your-first-love2d-game-in-200-lines-part-1-of-3

Nice thx