Animator source

-- Animation class
--
-- Create with Animator(start, stop, time, easing, callback)
-- "start" is the start value
-- "end" is the end value
-- "time" is the time taken, in seconds, to complete the animation
-- "easing" is the easing of the animation (how it slows down/speeds up)
-- use EASENONE, EASEIN, EASEOUT, or EASEBOTH
-- "callback" is the function that is called once the animation is 
-- complete
--
-- Get the current value of the animation with
-- Animator:value()
-- This will call the callback function if the function is complete
-- (it only calls it once)
-- 
-- You can also get the value at any time t between 0 and 1 using
-- Animator:valueAt(t, [easing])

EASENONE = 1
EASEIN = 2
EASEOUT = 3
EASEBOTH = 4

Animator = class()

function Animator:init(start, stop, time, easing, callback)
    self.start = start
    self.stop = stop
    self.stopTime = time
    self.startTime = ElapsedTime
    self.easing = easing or EASENONE
    self.complete = false
    self.callback = callback or function() end
end

function Animator:valueAt(t, easing)
    easing = easing or self.easing
    if self.easing == EASENONE then
        value = t * (self.stop - self.start) + self.start
    elseif self.easing == EASEOUT then
        value = math.sin(math.pi/2 * t)*
                (self.stop-self.start)+self.start
    elseif self.easing == EASEIN then
        value = (-math.cos(math.pi/2 * t)+1)*
                (self.stop-self.start)+self.start
    elseif self.easing == EASEBOTH then
        value = (-math.cos(math.pi * t)+1)/2*
                (self.stop-self.start)+self.start
    end
    return value
end

function Animator:value()
    time = (ElapsedTime - self.startTime)/self.stopTime
    time = math.min(time, 1)
    if time == 1 then
        if not self.complete then
            self.complete = true
            self.callback()
        end
        return self.stop
    else
        return self:valueAt(time)
    end
end