local cube = dofile("include/cube.lua")
local d=0
return function (page, offset, screen_width, screen_height)
local percent = math.abs(offset/page.width)

if percent < 0.02 then
d = math.random(1, 4)
end
local sign = 0
if offset > 0 then sign=1 end
if offset <=0 then sign=-1 end
offset = math.abs(offset)
    offset = (offset - (0.02 * page.width)) * 100/98
if offset <0 then offset=0 end
offset = sign * offset
    local x, z, angle = cube(page, offset, false, d)

    local threshold = math.abs(math.atan((PERSPECTIVE_DISTANCE - z)/x))
    angle = math.abs(angle)

    if angle > threshold then
        page.alpha = 1 - (angle - threshold)/(math.pi/2 - threshold)
    else
        page.alpha = 1
    end
    if percent > 0.98 then
        page.alpha = 0
    end
end