Initial untested code.

Color.lua

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+--[[
+	Colors related µLua compatibility layer/lib for ctrµLua
+]]
+
+Color = {}
+
+function Color.new(r, g, b)
+	r = r*8
+	g = g*8
+	b = b*8
+	return (r+g*256+b*65536)
+end
+
+function Color.new256(r, g, b)
+	return (r+g*256+b*65536)
+end

screen.lua

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+--[[
+		Screen related µLua compatibility layer/lib for ctrµLua
+
+	Warning: as µLua API was created with the ass, all functions are declared as
+globals. Keep this in mind.
+	Also, not all the functions are implemented, it won't trigger errors but just
+won't draw some things.
+	The screen size is a real problem when you write something like this, so by
+default the library uses NDS screen size, but you can change it to the 3DS size.
+	Finally, µLua draw 1 screen each frame at 60 FPS, so to avoid graphical bugs
+I had to reproduce this. That's bad, but I want something as close to the
+original µLua as possible.
+
+	µLua have ~4MB of RAM available to the user, so using some more bytes for this
+library shouldn't be a problem :). Same thing for the CPU.
+]]
+
+-- Constants
+
+SCREEN_WIDTH = 256
+SCREEN_HEIGHT = 192
+--SCREEN_WIDTH = 320 -- uncomment for a larger screen
+--SCREEN_HEIGHT = 240 -- idem
+SCREEN_UP = 0
+SCREEN_DOWN = 1
+ALPHA_RESET = 100
+
+NB_FPS = 0
+
+-- Local
+
+local ctr = require("ctr")
+local gfx = require("ctr.gfx")
+
+-- As the µLua and ctrµLua drawing systems are very differents, we have to use a
+-- stack. That's bad, but it's the only solution.
+local videoStack = {}
+
+local alpha = ALPHA_RESET
+
+local drawScreen = SCREEN_UP
+
+local fpscount = 0
+local fpstime = ctr.time()
+
+local function RGB2RGBA(c)
+	return (c*256)+alpha)
+end
+
+-- Module
+function startDrawing()
+	screen.startDrawing2D()
+end
+
+function stopDrawing()
+	-- As you can change the screen size, we have to re-calculate this every time.
+	local offsetX = (gfx.BOTTOM_WIDTH-SCREEN_WIDTH)/2
+	local offsetY = (gfx.BOTTOM_HEIGHT-SCREEN_HEIGHT)/2
+	if drawScreen == gfx.SCREEN_UP then
+		offsetX = offsetX + 40
+	end
+	
+	-- FPS counter
+	fpscount = fpscount + 1
+	if (ctr.time() - fpstime) > 1000 then
+		NB_FPS = fpscount
+		fpscount = 0
+	end
+	
+	-- render
+	screen.endDrawing()
+	
+	-- set the screen
+	drawScreen = ((drawScreen == 0 and 1) or 0)
+end
+
+function render()
+	startDrawing()
+	stopDrawing()
+end
+
+screen = {}
+
+function screen.switch()
+	SCREEN_UP, SCREEN_DOWN = SCREEN_DOWN, SCREEN_UP
+end
+
+function screen.getLayer()
+	return #videoStack[drawScreen]
+end
+
+function screen.getAlphaLevel()
+	return ALPHA_RESET
+end
+
+function screen.setAlpha(level, layer)
+	alpha = level
+end
+
+function screen.print(scr, x, y, text, color)
+	videoStack[scr][#videoStack[scr]] = {"text", {x, y, text, 8, RGB2RGBA(color), nil}}
+end
+
+function screen.printFont(scr, x, y, text, color, font)
+	videoStack[scr][#videoStack[scr]] = {"text", {x, y, text, 8, RGB2RGBA(color), font}}
+end
+
+function screen.blit(scr, x, y, img, sx, sy, w, h)
+	local sizex, sizey = img:getSize()
+	videoStack[scr][#videoStack[scr]] = {"img", {x, y, (sx or 0), (sy or 0), (w or sizex), (h or sizey)}}
+end
+
+function screen.drawPoint(scr, x, y, color)
+	videoStack[scr][#videoStack[scr]] = {"point", {x, y, RGB2RGBA(color)}}
+end
+
+function screen.drawLine(scr, x0, y0, x1, y1, color)
+	videoStack[scr][#videoStack[scr]] = {"line", {x0, y0, x1, y1, RGB2RGBA(color)}}
+end
+
+function screen.drawRect(scr, x0, y0, x1, y1, color)
+	videoStack[scr][#videoStack[scr]] = {"line", {x0, y0, x0, y1, RGB2RGBA(color)}}
+	videoStack[scr][#videoStack[scr]] = {"line", {x0, y0, x1, y0, RGB2RGBA(color)}}
+	videoStack[scr][#videoStack[scr]] = {"line", {x0, y1, x1, y1, RGB2RGBA(color)}}
+	videoStack[scr][#videoStack[scr]] = {"line", {x1, y0, x1, y1, RGB2RGBA(color)}}
+end
+
+function screen.drawFillRect(scr, x0, y0, x1, y1, color)
+	videoStack[scr][#videoStack[scr]] = {"rectangle", {x0, y0, (x1-x0), (y1-y0), 0, RGB2RGBA(color)}}
+end
+
+function screen.drawGradientRect(scr, x0, y0, x1, y1, color, color, color, color)
+
+end
+
+function screen.drawTextBox(scr, x0, y0, x1, y1, text, color)
+
+end
+
+function screen.drawTexturedQuad(scr, x0, y0, x1, y1, x2, y2, x3, y3, img, sx, sy, w, h)
+
+end
+
+function screen.drawTexturedTriangle(scr, x0, y0, x1, y1, x2, y2, img, sx, sy, w, h)
+
+end
+
+function screen.getMainLcd()
+	return (drawScreen == SCREEN_UP)
+end
+
+function screen.setSpaceBetweenScreens(space) -- deprecated in µLua 4.7.1
+
+end
+
+function screen.init() -- unused
+
+end
+
+function screen.startDrawing2D() -- unused
+		--reset the video stacks
+	videoStack = {}
+	videoStack[0] = {}
+	videoStack[1] = {}
+end
+
+function screen.endDrawing()
+	gfx.startFrame(drawScreen)
+	for i=1, #videoStack[drawScreen] do
+		local e = videoStack[drawScreen][i]
+		if e[1] == "img" then
+			
+		else
+			gfx[e[1]](unpack(e[2])
+		end
+	end
+	gfx.endFrame()
+	gfx.render()
+end
+
+function screen.waitForVBL() -- unused
+
+end

uCompat.lua

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+--[[
+	Main µLua compatibility layer/lib for ctrµLua
+
+	The goal is not to provide a full compatibility, but something close.
+]]
+
+-- Constants
+ULUA_VERSION = "4.7.2"
+ULUA_DIR = "sdmc:/3ds/ctruLua/"
+ULUA_SCRIPTS = (ULUA_DIR.."scripts/") -- Warning: you need to create the folder
+ULUA_LIBS = (ULUA_DIR.."libs/")
+ULUA_BOOT_FILE = "main.lua"
+ULUA_BOOT_FULLPATH = (ULUA_DIR..ULUA_BOOT_FILE)
+
+-- Other libs
+screen = require("uCompat.screen")