by
Voetsjoeba  9
December 2006
Easing is a way of moving from one location to another,
so that the speed of the object that moves along its
track varies. This tutorial will deal with a specific
type of easing called ‘Easing Out’; easing in a way so that the
object’s speed decreases as it nears its destination.
The complement of Easing Out is Easing In, and since
they are both similar, I will mention Easing In only in
passing towards the end of the tutorial.
Consider the following two examples to get a good grasp
of what the difference is between the two. Both
represent an object moving from the
left towards a destination on the right, but in two
different ways. The first one uses no easing at all ( a
constant speed ) to move to its destination, the second
uses ‘Easing Out’ to move to its destination. From now
on I will refer to ‘Easing Out’ as simply ‘easing’, for
the sake of consistency and readability.
The above example does not use any
easing. Notice how the square's speed stays constant
throughout the movement.
On the other hand, the above square
contains a slight easing. You should see the square
start to decelerate as it nears its destination.
So, easing as we’ll discuss it here is the way of moving
where an object slows down as it nears its goal. The key
to implementing this in Flash might be simpler than you
thought. What happens is basically you take the distance
between the object and its destination, divide it by a
number greater than 1, and you now have a distance that
is smaller. We then move our object to be at the newly
calculated distance from its destination, and repeat
this reduction as long as necessary.
Why does this make it ease? Well, since we’re dividing,
the greater the distance is between the object and its
destination, the greater the difference in calculated
distance will be in absolute terms. Put otherwise: the
closer the object gets to its goal, the smaller the
distance to the goal is. The smaller the distance to the
goal, the smaller the distance will be that we
calculate. The smaller the distance is that we
calculate, the less we move the object moves towards its
goal. Thus we have easing movement.
That might sound a bit confusing. Consider the following
example: we have an object that is currently at position
0, and we want to ease it to position 120. We must first
pick a number to divide each distance by, as this will
determine the speed of our easing motion. Let’s pick 2.
We can now follow these steps:

Take the distance between the
object’s current position and its destination

Divide this distance by 2

Move the object towards its
destination, so that it is the distance we
calculated in step 2 away from it.

Repeat Step 1
Indeed, this is a loop, every iteration
through it updating the object’s position. To clarify
how it works, here’s a visual representation. The line
on the left indicates the object’s starting position
(0), and the line on the right indicates the object’s
destination (120). The orange line represents the
object’s new position, calculated by dividing the
distance between current position and destination by 2.
Considering that you can go on and on, always dividing
the distance by 2 (don’t worry about ending the loop
yet), we get the following movement pattern:
Now that you have an understanding of how to think
about easing out effects, let's delve into how easing
can be implemented in Flash.
