Animations with flash CS3 - spring and friction + mouse

[Flep]

Here we are with another article reguarding spring+friction.
For the ones who has not read: inertia,  acceleration , spring and spring and friction, I suggest to give them a look to understand what I will talk about next.
This time I will apply the effect based on the coordinates of the user's mouse.
I would like to point to the fact that the applied effect is very simple and not very exciting. As always, this article would like to be a tutorial before an animation and so, I let space to your fantasy to apply other solutions to obtain animations up to your applications.
Let's get into it...


I create a FLA and save it as 'spring_2.fla', into which I create a MovieClip (of whatever shape) and to which I assign the instance name 'square_mc'.
I create a Document Class, an AS file saved as 'Sprin2.as', implemented the following way:

import flash.display.MovieClip;
	import flash.events.Event;
	
	public class Spring2 extends MovieClip
	{
		private const spring:Number=.1;
		private const frizione:Number=.9;
		private var vel_x:Number=0;
		private var vel_y:Number=0;

		public function Spring2()
		{
			init();
		}
		
		private function init():void
		{
			stage.frameRate=31;
			
			square_mc.addEventListener(Event.ENTER_FRAME,muovi);
		}
		
		private function muovi(e:Event):void
		{
			var acc_x:Number=(mouseX-square_mc.x)*spring;
			var acc_y:Number=(mouseY-square_mc.y)*spring;
			vel_x+=acc_x;
			vel_y+=acc_y;
			vel_x*=frizione;
			vel_y*=frizione;
			square_mc.x+=vel_x;
			square_mc.y+=vel_y;
		}
	}
}

The result:

Let's analise the code.

Properties
a numerical constant 'spring'
private const spring:Number=.1;
a numerical constant 'frizione'
private const frizione:Number=.9;
the two speeds which will be modified by the spring and friction before being passed to X and Y
private var vel_x:Number=0;
private var vel_y:Number=0;

Methods
init();
I impost the frame rate
stage.frameRate=31;
I add an interval ENTER_FRAME which calls the function muovi() as many times by seconds as the value of the frame rate
square_mc.addEventListener(Event.ENTER_FRAME,muovi );

muovi();
I create a variable which contains the value of the inertia effect applied to the mouse coordinates and I add the spring effect
var acc_x:Number=(mouseX-square_mc.x)*spring;
var acc_y:Number=(mouseY-square_mc.y)*spring;
I add to vel_x and vel_y ( at each interval's iteration) the inertia
vel_x+=acc_x;
vel_y+=acc_y;
I apply the friction to vel_x and vel_y
vel_x*=frizione;
vel_y*=frizione;
I pass vel_x and vel_y to the x and y of 'square_mc'
square_mc.x+=vel_x;
square_mc.y+=vel_y;

Stay tuned !

[SwalifNet]

thanks