I'm modeling a vector field in flash and spawning a mess of particles to visualize the flow of the field. Using the vector field F(x,y)=yi-xj
This vector field has a curl, the particles are to move in circles which they do. My problem is that the particles diverge from the origin, though this particular vector field has no divergence. I suspect that my data types may be losing decimal precision during the very basic caluclations for this field or perhaps I'm making some logic mistake I am unsure.
This code spawns the particles on the screen (which is 800x450). This code probably isn't in trouble, but for completeness I included it.
//spawn particles
var i:int;
var j:int;
//spread is the spacing between particles
var spread:Number;
spread = 10.0;
//spawn the particles
for (i=0; i<=800/spread; i++)
{
for (j=0; j<=450/spread; j++)
{
//computes the particles position and then constructs the particle.
var iPos:Number = spread * Number(i) - 400.0;
var jPos:Number = 225.0 - spread * Number(j);
var particle:dot = new dot(iPos,jPos,10.0);
addChild(particle);
}
}
This is the "dot" class which contains everything important about the particles being spawned.
package
{
//import stuff
import flash.display.MovieClip;
import flash.events.Event;
public class dot extends MovieClip
{
//variables
private var xPos:Number;
private var yPos:Number;
private var xVel:Number;
private var yVel:Number;
private var mass:Number;
//constructor
public function dot(xPos:Number, yPos:Number, mass:Number)
{
//Defines the function to be called when the stage advances a frame.
this.addEventListener(Event.ENTER_FRAME, moveDot);
//Sets variables from the constructor's arguments.
this.xPos = xPos;
this.yPos = yPos;
this.mass = mass;
//Set these equal to 0.0 so the Number type knows I want a decimal (hopefully).
xVel = 0.0;
yVel = 0.0;
}
//Controlls the particle's behavior when the stage advances a frame.
private function moveDot(event:Event)
{
//The vector field is a force field. F=ma, so we add F/m to the velocity. The mass acts as a time dampener.
xVel += yPos / mass;
yVel += - xPos / mass;
//Add the velocity to the cartesian coordinates.
xPos += xVel;
yPos += yVel;
//Convert the cartesian coordinates to the stage's native coordinates.
this.x = xPos + 400.0;
this.y = 225.0 + yPos;
}
}
}
Ideally the particles would all move in circles about the origin forever. But the code creates a situation where the particles rotate around the origin and spiral outwards, eventually leaving the stage. I'd really appreciate a helping hand. Thanks!
You can normalize each particle's distance from origin (maybe not on each step to save calculations). Also it seems your code is not optimized - you are creating ENTER_FRAME listener for every particle, and there is 3600 of them. One listener should be enough. And I would change all these divisions to multiplication by inverse value.