class Particle{

  PVector velocity, location; //PVector variables for each particle.

  Particle(){ //Constructor - random location and speed for each particle.
    velocity = new PVector(random(-0.5,0.5), random(-0.5,0.5));
    location = new PVector(random(0,width),random(0,width));
  }

  void update() { location.add(velocity); } //Motion method.

  void edge() {  //Wraparound case for particles.
    if (location.x > width) {location.x = 0;} 
    else if (location.x < 0) {location.x = width;}

    if (location.y > height) {location.y = 0;}
    else if (location.y < 0) {location.y = height;}
  }

  void display(ArrayList<Particle> p){ //Display method to show lines and ellipses between particles.

    for(Particle other: p){ //For every particle in the ArrayList.
     float d = PVector.dist(location,other.location); //Get distance between any two particle.
     float a = 255 - d*2.5; //Map variable 'a' as alpha based on distance. E.g. if distance is high, d = 100, alpha is low, a = 255 - 225 = 30.

     println("Lowest distance of any two particle =" + d); //Debug output.

     if(d<112){ //If the distance of any two particle falls bellow 112.
      noStroke(); //No outline.
      fill(0,a); //Particle are coloured black, 'a' to vary alpha.
      ellipse(location.x, location.y, 8, 8); //Draw ellipse based on location of particle.

      stroke(0,a); //Lines are coloured black, 'a' to vary alpha.
      strokeWeight(0.7);
      line(location.x,location.y,other.location.x,other.location.y); //Draw line between four coordinates, between two particle.
     }

    }
  }
}

ArrayList<Particle> particles = new ArrayList<Particle>(); //Create a new arraylist of type Particle.

void setup(){
  size(640,640,P2D); //Setup frame of sketch.
  particles.add(new Particle()); //Add five Particle elements into arraylist.
  particles.add(new Particle());
  particles.add(new Particle());
  particles.add(new Particle());
  particles.add(new Particle());
}

void draw(){
 background(255); //Set white background.
 for(Particle p: particles){ //For every 'p' of type Particle in arraylist particles.
   p.update(); //Update location based on velocity.
   p.display(particles); //Display each particle in relation to other particles.
   p.edge(); //Wraparound if particle reaches edge of screen.
 }
}

在上面的代码中，有对对象、线条和椭圆进行整形。其透明度受变量a的影响。

变量“a”或alpha是从距离“d”推断出来的。因此，当对象更远时，对象的alpha值会下降。

在这种情况下，线的alpha值不会随着时间的推移而改变，例如随距离渐隐。然而，尽管代码非常相似，椭圆似乎卡在alpha'255'上。

如果'a'的值是硬编码的，例如。

if(d<112){ //If the distance of any two particle falls bellow 112.
      noStroke(); //No outline.

      fill(0,100); //Particle are coloured black, set alpha 'a' to be 100, grey tint.

      ellipse(location.x, location.y, 8, 8); //Draw ellipse based on location of particle.

椭圆按预期将颜色变为灰色。

编辑：我相信我已经找到了问题的根源。变量“a”不区分正在迭代的粒子。因此，alpha可能会卡住/加起来是255。