love2d postprocessing

assert(love.graphics, 'This module require love.graphics module')
local graphics = love.graphics
local buffer = graphics.newCanvas()
local resX, resY = graphics.getDimensions()
return function(canvas, shader, clear)
	assert(canvas:type() == 'Canvas', 'Argument #1 error: love2d-canvas expected. Use post processing only with canvases.')
	assert(shader:type() == 'Shader', 'Argument #2 error: love2d-shader expected.')
	local x, y = graphics.getDimensions()
	if x ~= resX or y ~= resY then buffer = graphics.newCanvas(); resX, resY = x, y end
	graphics.push('all')
		graphics.setCanvas(buffer)
		if clear then	graphics.clear(0.0, 0.0, 0.0, 0.0) end
		graphics.setShader(shader) graphics.draw(canvas) graphics.setShader()
		graphics.setCanvas(canvas) graphics.draw(buffer)
	graphics.pop()
end


--[[
Reference:
postprocessing = require 'module' -- replace 'module' to your file
framebuffer = love.graphics.newCanvas()

love.graphics.setCanvas(framebuffer)
--draw any stuff
love.graphics.setCanvas()

postprocessing(framebuffer, shader1)	-- apply first shader
postprocessing(framebuffer, shader2)	-- apply second shader

love.graphics.draw(framebuffer)			-- draw buffers with postprocessing
]]