-- Cool Tunnel
local rnd=math.random
local ins,rem=table.insert,table.remove
local back={}

local ring
local t
local W,H
function back.init()
    ring={}
    t=26
    back.resize(SCR.w,SCR.h)
end
function back.resize(w,h)
    W,H=w,h
end
function back.update(dt)
    t=t-1
    if t==0 then
        t=rnd(26,62)
        ins(ring,0)
    end
    for i=#ring,1,-1 do
        ring[i]=ring[i]+dt
        if ring[i]>3.55 then
            rem(ring,i)
        end
    end
end
function back.draw()
    GC.clear(.08,.08,.084)
    GC.setColor(1,1,1,.1)
    for i=1,#ring do
        local r=ring[i]^2/12
        GC.setLineWidth(30-15/(r+.5))
        GC.rectangle('line',W*.5-W*r/2,H*.5-H*r/2,W*r,H*r)
    end
end
function back.discard()
    ring=nil
end
return back