Flash Actionscript 3.0：数字类型和小数精度（矢量场和粒子）

Question

我正在 Flash 中对矢量场进行建模，并生成一堆粒子来可视化场的流动。使用向量场F(x,y)=yi-xj

这个向量场有一个旋度，粒子将按其圆周运动。我的问题是粒子从原点发散，尽管这个特定的矢量场没有发散。我怀疑我的数据类型可能会在该字段的基本计算过程中丢失小数精度，或者我可能犯了一些我不确定的逻辑错误。

此代码在屏幕（800x450）上生成粒子。这段代码可能没有问题，但为了完整性我将其包含在内。

//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);
 }
}

这是“点”类，其中包含有关所生成的粒子的所有重要信息。

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;
  }
 }
}

理想情况下，粒子将永远绕着原点做圆周运动。但代码创建了一种情况，粒子围绕原点旋转并向外螺旋，最终离开舞台。我真的很感激您的帮助。 谢谢！

Answer 1

您可以标准化每个粒子距原点的距离（也许不是在每个步骤上以节省计算）。另外，您的代码似乎没有优化 - 您正在为每个粒子创建 ENTER_FRAME 侦听器，并且有 3600 个粒子。一名听众就足够了。我会将所有这些除法改为乘以逆值。

Answer 2

要设置小数位，请使用 toFixed() 函数。

//Set these equal to 0.0 so the Number type knows I want a decimal (hopefully).
 xVel = 0;
 yVel = 0;
 xVel.toFixed(1); //(specifies decimal places)
 yVel.toFixed(1);

希望有帮助