处理，无法为ArrayList中的对象设置alpha值-Java 学习之路

这是question的后续行动 .

我希望得到一堆粒子对象以保持某个'alpha'值 . 该α值将基于其与相邻粒子的接近度而增加/减少 .

目前我的代码导致所有粒子保持最大alpha值 . 我相信这是由于迭代通过ArrayList导致多次重绘alpha . 由于这个原因，该计划运行缓慢 .

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 - map(d,0,112,0,255); //Map variable 'a' as alpha based on distance. E.g. if distance is high, d = 100, alpha is low, a = 255 - 225 = 30.

if(other==this){continue;}

     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.

    }else{
      noStroke(); //No outline.
      fill(0,30); //For particles far away, set them to a fix alpha of '30'
      ellipse(location.x, location.y, 8, 8); //Draw ellipse based on location of particle.
    }
  }
}
}

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

void setup(){
  size(640,640,P2D); //Setup frame of sketch.

    for (int i=0; i<40; i++) { 
  particles.add(new Particle()); //Add five Particle elements into arraylist.
    }
}

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.
 }
}

1 回答

您从your previous question遇到同样的问题：对于每个 Particle ，您循环浏览 every 其他 Particle ，因此您最终会为每个 Particle 绘制40个省略号 . 相反，您需要遍历 Particle 并找到最近的邻居，然后将您的alpha计算基于 one Particle .

换句话说，您的绘图代码应该发生 after for 循环 .

找到最近的邻居看起来像这样：

Particle closestNeighbor = null;
float closestDistance = 100000;

for (Particle other : p) { //For every particle in the ArrayList.

  if (other == this) {
    continue;
  }


  float d = PVector.dist(location, other.location);
  if (d < closestDistance) {
    closestDistance = d;
    closestNeighbor = other;
  }
}

此循环完成后， closestNeighbor 将指向最近的邻居， closestDistance 将是最近的距离 . 您可以在计算alpha时使用它：

float a = 255 - map(closestDistance, 0, 112, 0, 255); //Map variable 'a' as alpha based on distance. E.g. if distance is high, d = 100, alpha is low, a = 255 - 225 = 30.

if (closestDistance<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.
} else {
  noStroke(); //No outline.
  fill(0, 30); //For particles far away, set them to a fix alpha of '30'
  ellipse(location.x, location.y, 8, 8); //Draw ellipse based on location of particle.
}

回复于 2024-04-28T21:53:38+08:00

处理，无法为ArrayList中的对象设置alpha值

1 回答

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