正在处理，无法为ArrayList中的对象设置Alpha值

Question

这是此question的后续操作。

我正在寻找一堆粒子物体以保持某个'alpha'值。此Alpha值将根据其与相邻粒子的邻近性而增加/减少。

目前我的代码导致所有粒子停留在max alpha。我相信这是由于迭代通过ArrayList结果中的alpha被重绘多次。由于这个，程序运行缓慢。

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. 
} 
} 

Answer 1

你必须从your previous question同样的问题：每个Particle，你通过每其他Particle循环，所以你最终绘制椭圆40为每一个Particle。相反，您需要循环访问Particle并找到最近的邻居，然后将您的阿尔法计算从该一个Particle。

换句话说，您的图纸代码后for循环。

定位最近的邻居是这样的：这个循环完成

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; 
    } 
} 

后，closestNeighbor将指向最近的邻居，和closestDistance将是最近距离。你可以使用这个在Alpha的计算：

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. 
}