Using getPixel and setPixel

[Maholain]

I was looking at the getPixel API and saw it's synopsis as this:

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r, g, b, a = ImageData:getPixel( x, y )

I was wondering, how would I compare what it returns in an if statement? I'm not sure what to do when it returns more than one thing.

Also, when I used setPixel in the update method, I got a 'attempt to access index 'ImageData'. Can someone tell me what is going wrong here?

[Robin]

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local r, g, b, a = ImageData:getPixel(x, y)
-- compare r, g, b, a
-- OR
local t = {ImageData:getPixel(x, y)} -- d'oh!
-- compare t[1], t[2], t[3], t[4]

[bartbes]

That second one is wrong

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local t = {ImageData:getPixel(x, y)}

[Maholain]

I'm trying to set the pixel below the cursor to say green if the pixel below my cursor is black.

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--In load
coverData = love.image.newImageData("overlay.png");
--in Update
if love.mouse.isDown("l") then
		local r, g, b, a = coverData:getPixel(love.mouse.getX(), love.mouse.getY());
		if (r,g,b,a == 0, 0, 0, 255) then
			coverData:setPixel(love.mouse.getX(), love.mouse.getY(), 40, 40, 40, 255);
		end
	end

It doesn't work and I'm wondering if anyone can provide me with a working sample.

[thelinx]

what am I thinking

[vrld]

dont look please

This won't work, because t is a different table than {0,0,0,255} even if t = {0,0,0,255}.
This should work:

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local r, g, b = coverData:getPixel(love.mouse.getX(), love.mouse.getY());
if r + g + b == 0 then
    coverData:setPixel(love.mouse.getX(), love.mouse.getY(), 40, 40, 40)
end

But expect it to be very, very slow...

[Maholain]

Thanks. I still can't get my initial idea to work though. I think it's because

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coverData:setPixel(love.mouse.getX(), love.mouse.getY(), 40, 40, 40, 255);

is only setting the pixel on coverData. I can't draw a ImageData though, so how can I show this coverData on the screen?

[thelinx]

Convert it into an image, draw that image.

[Maholain]

Convert it into an image, draw that image.

Neat! Thanks, problem solved. The code I used if anyone is interested:

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--This code will reveal what's behind it because of setPixel being set to invisible
function love.update(dt) 
	if love.mouse.isDown("l") then
		local r, g, b = coverData:getPixel(love.mouse.getX(), love.mouse.getY());
			if r + g + b == 0 then
				coverData:setPixel(love.mouse.getX(), love.mouse.getY(), 0, 0, 0, 0)
		end
	end
	imagesData = love.graphics.newImage(coverData);
end
function love.draw() 
	love.graphics.draw(imagesData, 0, 0);
end

[leiradel]

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if (r,g,b,a == 0, 0, 0, 255) then

You can't compare multiple values like that AFAIK. Use

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if r == 0 and g == 0 and b == 0 and a == 255 then[/quote]

Summing r, g and b and comparing against zero is more efficient I think, but it only works for black (sum == 0) and white (sum == 765).

Cheers,

Andre