Space Invaders Lesson 10 – More Arrays and Loops

-- title:  Space Invaders
-- author: Bob Grant
-- desc:   Lesson 10
-- script: lua

playerShip = {

	position = {
		x = 120,
		y = 128
	},
	
	spriteNum = 0,
	minX = 0,
	maxX = 232,
	speed = 1,
	
	bulletOffset = {
		x = 4,
		y = 4
	}
}

playerBullets = {}
maxPlayerBullets = 5
gameNeedsToBeInitialised = true

function TIC()

 -- game initialisation
 -- check if game needs to be initialised
	if (gameNeedsToBeInitialised) then
		initialiseGame()
		gameNeedsToBeInitialised = false
	end
	
	-- updating
	
	movePlayerShip()
	
	checkPlayerFire()
	movePlayerBullet()
	
	
	-- drawing / rendering
	
	cls()
	
	drawPlayerBullet()
	
	drawPlayerShip()
	
	
end -- end TIC

function movePlayerShip()

	-- check move right button
	if(btn(2)) then
	 playerShip.position.x = 
			playerShip.position.x - playerShip.speed
	end
	-- check move left button
	if(btn(3)) then
	 playerShip.position.x = 
			playerShip.position.x + playerShip.speed
	end
	
	playerShip.position.x = checkLimits(
		playerShip.position.x,
		playerShip.minX,
		playerShip.maxX )

end -- movePlayerShip

function checkLimits(value, min, max)

	if (value > max) then
		value = max
	elseif (value < min) then
		value = min
	else
		value = value
	end
	
	return value

end -- checkLimits

function checkPlayerFire()

	local bulletFired = false
	
	-- if fire button is pressed then
	if (btnp(4)) then
		--  find a bullet that's ready to fire
	 for bullet = 1,maxPlayerBullets do
			if (bulletFired == false) then
				if (not playerBullets[bullet].active) then
						--   initialise bullet
						playerBullets[bullet].position = {
							x = playerShip.position.x + playerShip.bulletOffset.x,
							y = playerShip.position.y + playerShip.bulletOffset.y
						}
						--   mark bullet as active
						playerBullets[bullet].active = true
						--   stop other bullets from firing
						bulletFired = true
				end -- if not active
			end -- if not bulletfired
	
		end -- for

	end -- if button pressed
	
end -- checkPlayerFire

function movePlayerBullet()

	for bullet = 1, maxPlayerBullets do
	
		if (playerBullets[bullet].active) then
			-- move the bullet up the screen
			playerBullets[bullet].position.y = 
			playerBullets[bullet].position.y - playerBullets[bullet].speed
			
			if (playerBullets[bullet].position.y < 0) then
				playerBullets[bullet].active = false
			end
		end
		
	end
		
end -- movePlayerBullet

function drawPlayerBullet()

	for bullet = 1, maxPlayerBullets do
	
		if (playerBullets[bullet].active) then
		
			-- draw player bullet
			-- line(startX, StartY, endX, endY, colour)
			line(
				playerBullets[bullet].position.x,
				playerBullets[bullet].position.y,
				playerBullets[bullet].position.x,
				playerBullets[bullet].position.y + playerBullets[bullet].length,
				playerBullets[bullet].colour
			)
		
		end -- if
	
	end -- for

end -- drawPlayerBullet

function drawPlayerShip()

	spr(playerShip.spriteNum, 
		playerShip.position.x, 
		playerShip.position.y, 0)


end -- drawPlayerShip

function initialiseGame()

	initPlayerBulletsArray()

end -- initialiseGame

function initPlayerBulletsArray()

	for bullet = 1, maxPlayerBullets do
		playerBullets[bullet] = {
			position = {
				x = 0,
				y = 0
			},
	
			length = 5,
			colour = 14,
			speed = 2,
			active = false
		}
	end -- for

end -- initPlayerBulletsArray