Class member variables?

[Afr0]

First off, I'm sorry for all my questions, but classes in Lua still has me a bit confused.
Please bear with me here!

Code: Select all

TileMap = {}
TileMapMT = { __index = TileMap } --This metatable will be attached to every created class instance.

TileMap.Tiles = {}
for i = 1,2 do
	TileMap.Tiles[i] = love.graphics.newImage("Tiles/Tile"..i..".png")
end

TileMap.Map = {}

function TileMap:Create()
	local NewInstance =
	{
		MapWidth = 20,
		MapHeight = 20,
		MapX = 0,
		MapY = 0,
		MapOffsetX = 30,
		MapOffsetY = 30,
		MapDisplayWidth = 14,
		MapDisplayHeight = 10,
		TileWidth = 32,
		TileHeight = 32
	} --The new instance
	setmetatable(NewInstance, TileMapMT)
	
	return NewInstance
end

function TileMap:Draw()
	for y=1, MapDisplayHeight do
      for x=1, MapDisplayWidth do                                                         
         love.graphics.draw( 
            Tiles[Map[y+MapY][x+MapX]], 
            (x*TileWidth)+MapOffsetX, 
            (y*TileHeight)+MapOffsetY)
      end
   end
end

In the TileMap:Draw() function, I'm trying to reference the members inside of NewInstance. This doesn't seem to work. I tried putting 'TileMap.' in front of the variable names, but that didn't work either.
Specifically, the error I'm getting is Tilemap.lua:31:'for' limit must be a number.

I thought about declaring my variables outside of the Create() function, but then how would I make them a part of a new instance?

Edit: I looked here, and it seems to suggest using self (similar to 'this' in C++). I tried doing it:

Code: Select all

function TileMap:Draw()
	for y=1, self.MapDisplayHeight do
      for x=1, self.MapDisplayWidth do                                                         
         love.graphics.draw( 
            self.Tiles[self.Map[y+self.MapY][x+self.MapX]], 
            (x*self.TileWidth)+self.MapOffsetX, 
            (y*self.TileHeight)+self.MapOffsetY)
      end
   end
end

But then I get an error saying 'Tried to access self: a nil value'...?

[bartbes]

Use self (so self.MapDisplayWidth)

[Robin]

Good, you're half way there.

The final thing is that where you call Draw, change the . to :

Code: Select all

someinstance:Draw()

That translates to:

Code: Select all

someinstance.Draw(someinstance)

Just like

Code: Select all

function t:func ()

translates to

Code: Select all

function t.func(self)

[Afr0]

Sigh, I did that. Now it says "TileMap.lua:34:Tried to access field '?' a nil value"

I'm confused!

Thanks though!

Edit:

Here's my main code:

Code: Select all

require("PlayerShip")
require("Bullet")
require("TileMap")

function love.load()
	love.graphics.setBlendMode('alpha')
	--love.graphics.toggleFullscreen()
	
	PShip = PlayerShip.Create()
	Map = TileMap.Create()
	
	Bullets = {}
	BulletIndex = 1
end

function love.keypressed(k)
	if k == 'escape' then
		love.event.push('q') --Quits the game
	end
	
	--TODO: Create bullet instance and add to array!
	if k == 'lctrl' then
		Bullets[BulletIndex] = Bullet.Create()
		Bullets[BulletIndex].X = PShip.X - 3
		Bullets[BulletIndex].Y = PShip.Y - 20
		
		BulletIndex = BulletIndex + 1
	end
end

function love.update(dt)
	if love.keyboard.isDown('up') then
		PShip.Y = PShip.Y - 2
	end
	
	if love.keyboard.isDown('down') then
		PShip.Y = PShip.Y + 2
	end
	
	if love.keyboard.isDown('left') then
		PShip.X = PShip.X - 2
	end
	
	if love.keyboard.isDown('right') then
		PShip.X = PShip.X + 2
	end
	
	for i = 1, 1000 do
		if Bullets[i] then
			Bullets[i].Y = Bullets[i].Y - 3
			
			if(Bullets[i].Y < 0) then
				Bullets[i] = nil
			end
		end
	end
	
	--Reset the Index when 1000 is reached so that new bullets will be inserted at the beginning of the array.
	if BulletIndex >= 1000 then
		BulletIndex = 1 
	end
end

function love.draw()
	love.graphics.draw(PShip.Image, PShip.X, PShip.Y)
	
	Map:Draw()
	
	for i = 1, 1000 do
		if Bullets[i] then
			love.graphics.draw(Bullets[i].Image, Bullets[i].X, Bullets[i].Y)
		end
	end
end

[Robin]

Which line is 34?

It probably contains

Code: Select all

t[x]

where t is a table and x some expression. It means x evaluates to nil, which cannot be used as table key.

[Afr0]

Line 34:

Code: Select all

            self.Tiles[self.Map[y+self.MapY][x+self.MapX]], 

I tried changing MapY and MapX to 1, since my Tiles array starts at 1
I.E:

Code: Select all

	local NewInstance =
	{
		MapWidth = 20,
		MapHeight = 20,
		MapX = 1,
		MapY = 1,
		MapOffsetX = 30,
		MapOffsetY = 30,
		MapDisplayWidth = 14,
		MapDisplayHeight = 10,
		TileWidth = 32,
		TileHeight = 32
	} --The new instance

But the error still persists!

Edit: D'oh! It's because I haven't filled out my Map array yet!