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All the actionscript is
on the first frame of the main timeline.
First the variables are "easing" and "target_x"
are declared, defined as numbers and then
assigned values.
var easing:Number = 0.2;
var target_x:Number = Stage.width/2;
ball_mc._x = 10;
A function is created to act on the movie clip "ball_mc" .
ball_mc.onEnterFrame
= function(){
ball_mc._x += (target_x - ball_mc._x)*easing;
};
The event handler
"onEnterFrame" calls the function every
time a new frame is entered. When the function
is called it finds
the difference between the present x position
of the movie clip
"ball_mc" and the target position "target_x",
target_x - ball_mc._x
multiplies the difference
by the easing factor,
(target_x - ball_mc._x)*easing;
then adds the result to the
present x coordinate value of the movie clip "ball_mc._x".
ball_mc._x += (target_x - ball_mc._x)*easing;
This reevaluation of the position
of ball_mc is done every time a frame is entered.
That is 24 times a second the position of the movie
clip is calculated and positioned.
With an easing factor that is smaller
than one the value that is added to the horizontal
position of the movie clip decreases each time
the function is called. The net effect is to make
the ball appear to decelerate as it approaches the
target value.
For example:
If the value of ease is set to 0.5 the amount added
to the x coordinate will be half the separation distance.
var easing:Number = 0.5;
var target_x:Number = 300;
ball_mc._x = 0;
ball_mc.onEnterFrame = function(){
ball_mc._x += (target_x - ball_mc._x)*easing;
};
- The first time the function is called it will
calculate a a difference of 300 - 0 as the ball_mc
is at the point 0 and has a target point of 300.
The function then multiples this difference by
0.5 giving 150. This is then set as the new position
of the ball_mc.
- The function is called again
and calculates a difference of 300-150 = 150 multiples
by the easing factor 0.5 to give 75 then add this
to the x coordinate making a new position of 225.
- When the function is called
again the difference is 300-225 = 75 when multiplied
by the easing factor it becomes 37.5 and the new
x coordinate value becomes 225 + 37.5 = 262.5.
This process continues as the function
is repeatedly called and the total gets closer and
closer to 300.
150,
225,
262.5,
281.25,
290.6,
295.3,
297.65,
298.8,
299.4,
299.7,
299.85,
299.9,
299.95,
299.95,
299.95,
299.95,
299.95,
299.95,
299.95,
299.95,
299.95,
299.95, and so on.....
The final position of the movie clip is never quite
300. Mathematically if you were to have a perfectly
accurate result each time it would take an infinite
number of steps to reach the number 300. But you would
in theory arrive at the number 300 exactly.
In Flash however
there is a limit to the precision of the calculated
values and so the value never exceeds 299.95.
But the since the function is called every time it
enters a frame it continues to calculate and reposition
the mc for as long as the user continues to view the
swf.
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