StepMania 5 - BGAnimation Help

local file = ... or "Square.png"

return LoadActor( file )..{
    OnCommand=function(self)
        self:playcommand("ResetPosition")
    end,
    ResetPositionCommand=function(self)

        -- reset the rotation ammount to 0
        -- reset x to be newly randomized
        -- and reset y to be offscreen below _screen.h
        self:rotationz(0)
            :x( _screen.w - math.random(0, _screen.w) )
            :y( _screen.h + self:GetHeight() )
            :diffuse(color("#5a5a5a"))
            :zoom(0.8)
            :queuecommand("Animate")
    end,
    AnimateCommand=function(self)

        -- tween duraiton of 2 seconds
        self:linear(2)
            -- tween the y position upwards until offscreen
            :y( -self:GetHeight() )
            -- rotate one full revolution on the z-axis
            :rotationz(360)
            -- and, finally, reset the position so we can do this again
            :queuecommand("ResetPosition")
    end
}