Voetsjoeba | 9
So far we have focused on implementing
easing and making the implementation more portable (see
previous page), but there
are some edge cases that we will need to address before you
can use this effect without running into any issues.
Up till now, our method has always been using the
onEnterFrame handler of the MovieClip it was easing.
This is an issue when we want to ease a MovieClip that
already has an onEnterFrame handler set to perform some
other task. We can’t just assume that it’s ok for us to
overwrite any MovieClip’s onEnterFrame handler!
[ the MovieClip’s onEnterFrame handler directly sets its
own _x property – not good ! ]
Considering that every MovieClip instance listens to the
onEnterFrame event, the solution to this problem is
obvious: we’ll just use another MovieClip’s onEnterFrame
handler ! But which MovieClip ? It has to be one of
which be can be sure it has no onEnterFrame handler
already in use. The only way we can be sure about that,
is by spawning and using an auxiliary MovieClip. Because
our auxiliary MovieClip has just been created, we are
sure that it does not have an onEnterFrame handler
already in use.
So where do we spawn this auxiliary MovieClip ? Since
every MovieClip must be able to ease separately from any
other, we will create it inside the MovieClip we will be
easing. This also enables for easy targeting: our
auxiliary MovieClip will only need to target its parent
MovieClip to get a reference to the MovieClip it will be
A better way of doing it: delegating the onEnterFrame
to an auxiliary child MovieClip ]
Spawning MovieClips through ActionScript is done using
the createEmptyMovieClip function. The new MovieClip will be
created inside the MovieClip that called the method,
making the MovieClip that called the method the parent
of the newly created MovieClip. When creating it, you
must specify an instance name and a depth for the
MovieClip. The choice of these two values is important,
as they both have to be unique for each easing method.
Right now we’re seeing a method of easing along the X
axis, but we will also see methods for easing a
MovieClip’s width, height, y position, scale, etc.
That’s why we will now rename our easing function to
easeX, to differ between any additional future easing
methods. Because a MovieClip should be able to ease more
than 1 of these properties at the same time, we must
make sure that all the easing methods use different
auxiliary MovieClips that take care of the separate
easing loops. And to ensure they are all different, we
must ensure that they all have both consistently unique
instance names and consistently unique depths.
- // do nothing
Notice that we are now no longer just removing the
MovieClip’s onEnterFrame, but rather the entire
auxiliary MovieClip. This because when the easing
movement has ended, this extra MovieClip has lost its
purpose and should be deleted. For easy code adjustment
within the loop body, we have saved a reference to the
parent MovieClip being eased as _this, so that we need
only replace the this by _this in order to target the
MovieClip we’re easing instead of the auxiliary
So now, we can ease MovieClips around just like before,
but this time keeping their onEnterFrame handler intact.
Onwards to the next page!