Rotoscale

Rotscale.lua

-- rotoscale!
-- by eiyeron
-- 07/04/2015
-- a good old demo effect! :3
-- retroactive.me/retro-actif
-- thanks zep for everything!:)
-- for pico-8, the code and
-- voxatron!
-- iirc local vars are faster
local t, angle, scale = 0, 0, 1
---- temp variables
-- x/yp = after rotation
local x, y, xp, yp
--trigonometry precalc vars
local ca, sa
local cal, sal = {}, {}

local function _draw()
	-- for each row
	for x=0,127,1 do
		for y=0,127,1 do
			-- here goes the rotation!
			-- with real bits of scale!
			xp = ( cal[x]+sal[y]) /scale
			yp = (-sal[x]+cal[y]) /scale
			-- we're getting the pixel's
			-- color from the spritesheet.
			pset(x,y,sget(xp%32,yp%24))
		end
	end
end

local function _update()
	-- just making things move.
	t = t + 0.005
	scale = abs(cos(t*1.3)) * 3 + 1
	angle = angle + 0.01
	-- some quick precalculations
	ca,sa = cos(angle), sin(angle)
	-- prcalc distance rotations
	-- to render way faster
	for x=0,127,1 do
		y = x-64
		cal[x] = ca * y
		sal[x]	= sa * y
	end
end

-- you lost the game! :)