Paint program

[micha]

Sure.

The snippet creates a table of tables. Recall that you need to create a table before you can fill it:
This causes an error:

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a[1] = 5

This will work:

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a = {}
a[1] = 5

Now an 1D-array is a table with integer number as indices:

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a[1] = 1
a[2] = 5
a[3] = 7
...
a[100] = -1

To create an 1D-array with zero in each entry you can do this with a loop:

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a = {}
for i = 1,100 do
  a[i] = 0
end

Next, a 2D array is a 1D array, whose entries are 1D arrays.
So we next the above array-creation-code into itsself (and replace one of the loop variables by another one to avoid conflicts):

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a = {}
for i=1,100 do
  a[i] = {}
  for j = 1,50 do
    a[i][j] = 0
  end
end

This creates a 2D array of size 100x50. To access the entry in column 12 and row 45 you can use

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print(a[12][45])

Setting the value works the same way.

This, by the way, is also the method to store tile-based maps.

[tavuntu]

Hi, that piece of code creates n empty rows, where n=width and for each row creates m pixels, where m=height, something like this (with width=3 and height=3):

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-- First iteration (i=1,j=1):
{0}
-- 2nd iteration (i=1,j=2):
{0,0}
-- 3rd iteration (i=1,j=3):
{0,0,0}
--...
-- 6th iteration (i=2,j=3):
{0,0,0},
{0,0,0}
--.........
-- last iteration (i=3,j=3):
{0,0,0},
{0,0,0},
{0,0,0}

-- at the end the pixel table = 
  {{0,0,0},{0,0,0},{0,0,0}}

I hope I've helped, I could be wrong though.

[tavuntu]

oops, a little later.

[iPoisonxL]

This, by the way, is also the method to store tile-based maps.

Yeah, I've tried working with tilemaps before, I never really grasped the concept correctly. Thanks for explaining this to me! Now, to color the pixels white, I'd simply loop through all the array entries and check if their values are, let's say, the string "white"? And if yes, then color that pixel white?

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for i=1,#pixels do
  for j=1,#pixels[i] do
    if(pixels[i][j]=="white")then
      love.graphics.point(...) --this is the part where I can't figure out. I'm thinking pixels[i][j], but that doesn't work, since it's not a coordinate.
    end
  end
end

EDIT:

oops, a little later.

Thanks for helping nonetheless!

DOUBLE EDIT:
I tried something out, but it has huge performance issues in the love.draw, and it's not even drawing.

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g = love.graphics
m = love.mouse
function love.load()
	pixels = {}
	for i=1,600 do
		pixels[i]={}
		for j=1,800 do
			pixels[i][j]={}
		end
	end
	g.setColor(255,255,255,255)
	g.setCaption("p-a-int")
	width = g.getWidth()
	height = g.getHeight()
end

function love.update()
	pos = {m.getX(), m.getY()}
	if(m.isDown("r"))then
		pixels = {}
	end
	if(m.isDown("l"))then
		for i,v in pairs(pixels) do
			for j,z in pairs(v) do
				z = {1, pos}
			end
		end
	end
end

function love.draw()
	for i,v in pairs(pixels) do
		for j,z in pairs(v) do
			if(z[1]==1)then
				g.point(z[2][1], z[2][2])
			end
		end
	end
	g.print(love.timer.getFPS(), 10, 10)
	--g.print("Amount of pixels being drawn: "..table.length(pixels), 10, 30) to be remade later
end

[Ref]

No surprise that you aren't drawing anything.
Try replacing:

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 pixels = {}
   for i=1,600 do
      pixels[i]={}
      for j=1,800 do
         pixels[i][j]={}
      end
   end

with:

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pixels = {}
for y = 1, 600 do
    pixels[y] = {}
    for x = 1, 800 do
        pixels[y][x] = 0
     end
end

and

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 if(m.isDown("l"))then
      for i,v in pairs(pixels) do
         for j,z in pairs(v) do
            z = {1, pos}
         end
      end
   end

with

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if m.isDown('l') then pixels[m.getY()][m.getX()] = 1 end

and

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for i,v in pairs(pixels) do
      for j,z in pairs(v) do
         if(z[1]==1)then
            g.point(z[2][1], z[2][2])
         end
      end

with

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for y = 1, 600 do
    for x = 1, 800 do
       if pixels[y][x] = 1 then  g.point(x,y) end
    end
end

I think that should work - maybe.
Best

[iPoisonxL]

It works, but it has huge performance issues... I'm trying to do this without any imageData or canvases, is there any way to boost up performance? I understand that it goes through a 2D array of 480,000 entries every frame to check whether it's a 0 or a 1, but there must be a way...

[DaedalusYoung]

The way is to use at least imageData. Why don't you want to use that?

[iPoisonxL]

I need someone to at least explain to me what imageData is.

[DaedalusYoung]

I think you can view ImageData as a sort of virtual image file. It basically works the same as a 2D array, but much more optimised. You can't draw ImageData directly, just as you can't draw an image file without loading it first, so you'll need to create a new image using the ImageData as source every time it changes. Then simply draw that image as you would with any other image.

[tavuntu]

Your performace will always be by soil if you're using ImageData and manipulating it in real time (at least you use a low resolution or have a monster machine), even worse if you make a real image an draw it each time you draw a pixel on screen.

Look this, I'm using a 2D array here to draw in real time over the screen, I use ImageData only when loading/saving the image in/from a real file:
https://www.dropbox.com/s/xb4dbzjqtartt ... ditor.love