Images Moving Along A Defined Curve

#!/usr/bin/env lua5.1

require[[fp]]
require[[fptheme]]
require[[fpeffects]]

bg=fp.image{style = "background"}
images = {}
filenames = {"icon_AlarmClock.png", "icon_Browser.png", 
		"icon_Camera.png","icon_Email.png", 
		"icon_Gallery.png", "icon_Music.png",
		"icon_Settings.png"}

--define the movement curve
local pad = 30--pad between first icon and the top
local xoffset = 200 --the offset of x
local slope = 80 --the slope
local tall = 100 --the length of curve
function cal(m)
	 if not m then return false end
	 return tall*( (math.exp((m-xoffset)/slope) - 
		math.exp((-m+xoffset)/slope)) / 
		(math.exp((m-xoffset)/slope) + 
		math.exp((-m+xoffset)/slope)) +1) + pad
end


--place the icons
local N = #filenames -- icon number 
local gap = 50--starting point of the first icon and the gap
local t = 20 --size getting bigger
local fade = 80 --transparency
local geometry={}

for i = 1,N do 
	local f ="data/icon/"..filenames[i]
	images[i] =fp.create{type="image", file=f}
	
	if i<=(#filenames+1)/2 then
		geometry[i]={x=i*gap-i*t/2, y = cal(i*gap)-i*t/2, 
				w=i*t, h=i*t}
		images[i]:transform(geometry[i])
		images[i]:alpha_set(i*fade)
	else geometry[i] = {x=i*gap-t*(N-i+1)/2,
			y = cal(i*gap)-t*(N-i+1)/2, 
			w=t*(N-i+1), h=t*(N-i+1)}
		images[i]:transform(geometry[i])
		images[i]:alpha_set((N-i+1)*fade)
	end
end	

--set the timer for the movement
local k=1
t = fp.timer(0.5, function()
	for i = 1,N do
		images[i]:transform(geometry[(i+k-1)%N+1]) 
	end
	k = k+1
	return true 
		end )

text = fp.text{text="Icons moving automatically", x=100,y=250}
fp.begin()