SM5 falling sprites

local maxZ = 100
local maxZoom = 4
local minZoom = 1
local targetHalfWidth=16
local startingOffset=128
local minZ = 0
local minFallTime = 6
local fallTimeRange = 4
local numItems = 64


local function CalculateSpawnPosition()
    --1 is x, 2 is y
    local output = {0,0}
    local mode = math.random(1,4)
    if mode <= 2 then --top or bottom
        output[1]=(math.random(SCREEN_LEFT-startingOffset,SCREEN_RIGHT+startingOffset))
    else
        output[2]=(math.random(SCREEN_TOP-startingOffset,SCREEN_BOTTOM+startingOffset))
    end

    if mode==1 then
        output[2]=(SCREEN_TOP-startingOffset)
    elseif mode==2 then
        output[2]=(SCREEN_BOTTOM+startingOffset)
    elseif mode==3 then
        output[1]=(SCREEN_RIGHT+startingOffset)
    elseif mode==4 then
        output[1]=(SCREEN_LEFT-startingOffset)
    end
    return unpack(output)
end

local function CalculateTargetDestination()
    return math.random(SCREEN_CENTER_X-targetHalfWidth, SCREEN_CENTER_X+targetHalfWidth),
    math.random(SCREEN_CENTER_Y-targetHalfWidth, SCREEN_CENTER_Y+targetHalfWidth)
end

local fallingItem = Def.Sprite{
    Texture=THEME:GetPathG("Common", "window icon"),
    InitCommand=function(self) self:queuecommand("Fall") end,
    FallCommand=function(self) self:linear(0):xy(CalculateSpawnPosition(self)):z(maxZ):zoom(maxZoom)
    :linear(minFallTime+math.random()*fallTimeRange):xy(CalculateTargetDestination()):z(minZ):zoom(minZoom)
    :queuecommand("Fall") end,
}

local t = Def.ActorFrame{InitCommand=function(s) s:fov(60):SetDrawByZPosition(true) end}
t[#t+1] = Def.Quad{InitCommand=function(s) s:diffuse(color"#000000"):zoomx(SCREEN_WIDTH):zoomy(SCREEN_HEIGHT) end}
for i=1,numItems do
    t[i] = fallingItem
end
return t