Vortex (Zoom)

return function(page, offset, screen_width, screen_height)
    local percent = math.abs(offset/page.width)

    local centerX = page.width/2
    local centerY = page.height/2+7

    local const = 1.5
    local scale = percent - 0.35
    local factor = 20

    if scale < 0 then scale = 0 end

    local radius = 0.60 * page.width / const
    if radius > page.height then radius = 0.60 * page.height / (const + factor * scale)
    else radius = 0.60 * page.width / (const + factor * scale) end

    local theta = (2*math.pi)/#page.subviews

    local endStage1P = 1/3
    local endStage2P = 2/3

    local stage1P = percent*(1/endStage1P)
    if (stage1P > 1) then stage1P = 1 end

    local stage2P = (percent-endStage1P)*(1/(endStage2P-endStage1P))
    if (stage2P > 1) then stage2P = 1
    elseif (stage2P < 0) then stage2P = 0 end

    for i, icon in subviews(page) do
        local iconAngle = theta*(i-1) - math.pi/6 + stage2P*(math.pi/3)

        local begX = icon.x+icon.width/2
        local begY = icon.y+icon.height/2

        local endX = centerX+radius*math.cos(iconAngle)
        local endY = centerY-radius*math.sin(iconAngle)

        icon:translate((endX-begX)*stage1P, (endY-begY)*stage1P, 0)
        icon:rotate(-stage1P*((math.pi/2) + iconAngle))
    end

    page.alpha = 1 - stage2P
    page:translate(offset, 0, 0)
end