time = 0.5

--Create a window
window = Window:Create()
context = Context:Create(window)
world = World:Create()
camera = Camera:Create()
camera:Move(0,0,-3)
local light = DirectionalLight:Create()
light:SetRotation(35,35,0)

--Create an emitter
emitter = Emitter:Create(100) 

emitter:ClearAlphaControlPoints() --Remove default control points

emitter:AddAlphaControlPoint(0,0)  --at spawn the particle will have an alpha of 0 (fully transparent)
emitter:AddAlphaControlPoint(.5,1)  --halfway through the particle's lifetime alpha will be 1 (ie not transparent)
emitter:AddAlphaControlPoint(1,0)  --at death the particle will be fully transparent

while true do
    
    if window:Closed() or window:KeyHit(Key.Escape) then return false end

    Time:Update()
    world:Update()
    world:Render()

    if (window:KeyDown(Key.Up)) then
            time = time + 0.01 
    
    elseif (window:KeyDown(Key.Down)) then
    
            time = time - 0.01 
    end
    time = math.max(0,time)
    time = math.min(1,time)

    context:SetBlendMode(Blend.Alpha) 
    context:DrawText("At  "..(time*100) .. " percent of the particles life alpha will be :" .. emitter:GetAlphaAtTime(time) ,2,2) 

    context:Sync()
end