LÖVE

Posted: **Thu Aug 30, 2018 12:39 am**

I am trying to do some deferred rendering stuff and I need to write to multiple canvases at the same time.
I saw that you can do

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love.graphics.setCanvas(canvas1, canvas2)

and to test, I copied the example code from https://love2d.org/wiki/love.graphics.newShader

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local pixelcode = [[
void effects(vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords)
{
    // love_Canvases is a writable array of vec4 colors. Each index corresponds to a Canvas.
    // IMPORTANT: If you don't assign a value to all active canvases, bad things will happen.
    love_Canvases[0] = color;
    love_Canvases[1] = color + vec4(0.5);
    // etc.
}
]]

local testshader = love.graphics.newShader(pixelcode)
local w, h = love.graphics.getDimensions()

local canvas0 = love.graphics.newCanvas(w, h)
local canvas1 = love.graphics.newCanvas(w, h)



function love.draw()
	love.graphics.setCanvas(canvas0, canvas1)
	love.graphics.setShader(testshader)
	love.graphics.setColor(255, 0, 0, 255)
	love.graphics.polygon("fill", 100, 100, 200, 100, 200, 200, 100, 200)


	love.graphics.setCanvas()
	love.graphics.setShader()
	love.graphics.draw(canvas0)
end

And it draws a red square just how it should in love-0.10.2-win64
But when I run it in love-11.1.0-win64 and up, it throws me this error:

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Error

main.lua:12: bad argument #1 to 'newShader' (missing 'position' or 'effect' function?)


Traceback

[C]: in function 'newShader'
main.lua:12: in main chunk
[C]: in function 'require'
[C]: in function 'xpcall'
[C]: in function 'xpcall'

Am I doing something wrong?

Posted: **Thu Aug 30, 2018 6:05 am**

The signature of the effects function has changed with LÖVE 11.

Removed the 'void effects(...)' pixel shader entry point. Use the new 'void effect()' instead.

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void effect() {
...
}

Posted: **Thu Aug 30, 2018 7:57 am**

I see, thank you. I tried void effect, but not without the arguments. Is there a way to get the pixel position? I think I can pipe in and do everything else custom.

Posted: **Thu Aug 30, 2018 11:42 am**

Documentation is lacking in this regard. It has not been updated for 11 yet.
You can use love_PixelCoord:

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local gfx = love.graphics
local tex = gfx.newImage('texture.png')

local cvs1, cvs2 = gfx.newCanvas(256, 256), gfx.newCanvas(256, 256)
local shader = gfx.newShader([[
	uniform Image MainTex;

	void effect() {
		love_Canvases[0] = VaryingColor * Texel(MainTex, VaryingTexCoord.xy);
		love_Canvases[1] = vec4(love_PixelCoord.xy * 1 / 256, 1, 1);
	}
]])

function love.draw()
	gfx.setCanvas(cvs1, cvs2)
	gfx.setShader(shader)
	gfx.draw(tex)
	gfx.setCanvas()
	gfx.setShader()
	gfx.draw(cvs1)
	gfx.draw(cvs2, 0, 256)
end

I'm not sure this is the correct and best way to do this, but it works.

LÖVE

Love2D 11.1 Multiple Canvases void effects

Love2D 11.1 Multiple Canvases void effects

Re: Love2D 11.1 Multiple Canvases void effects

Re: Love2D 11.1 Multiple Canvases void effects

Re: Love2D 11.1 Multiple Canvases void effects