main.lua

debug = true

-- Timers
-- We declare these here so we don't have to edit them multiple places
canShoot = true
canShootTimerMax = 0.2 
canShootTimer = canShootTimerMax
--More timers
createEnemyTimerMax = 0.4
createEnemyTimer = createEnemyTimerMax
-- Image Storage
bulletImg = nil
enemyImg = nil -- Like other images we'll pull this in during out love.load function
-- Entity Storage
bullets = {} -- array of current bullets being drawn and updated
player = {x = 200, y = 710, speed = 150, img = nil}
enemies = {} -- array of current enemies on screen
-- Game stats
isAlive = true
score = 0

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')
	--we now have an asset ready to be used inside Love
end

function love.update(dt)
	setTimers(dt)
	getControls(dt)
	updateSprite(dt)
	checkCollision()
end

function love.draw(dt)
	if isAlive then
		love.graphics.draw(player.img, player.x, player.y)
		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
		love.graphics.print("Score: " .. score, love.graphics:getWidth()/2-50, 10)
	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 isCollision(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

function checkCollision()
-- 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 isCollision(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 isCollision(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
end

function setTimers(dt)
	-- Time out how far apart our shots can be.
	canShootTimer = canShootTimer - dt
	if canShootTimer < 0 then
	  canShoot = true
	end
	-- Time out enemy creation
	createEnemyTimer = createEnemyTimer - (1 * dt)
	if createEnemyTimer < 0 then
		createEnemyTimer = createEnemyTimerMax
		-- Create an enemy
		randomNumber = math.random(10, love.graphics:getWidth() - 10)
		newEnemy = { x = randomNumber, y = -10, img = enemyImg }
		table.insert(enemies, newEnemy)
	end
end

function getControls(dt)
	-- I always start with an easy way to exit the game
	if love.keyboard.isDown('escape') then
		love.event.push('quit')
	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 = 50
		player.y = 710

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

	if love.keyboard.isDown('space', '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)
		canShoot = false
		canShootTimer = canShootTimerMax
	end
end

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

		if enemy.y > 850 then -- remove enemies when they pass off the screen
			table.remove(enemies, i)
		end
	end
end