almost flow.pde

//from youtube video https://www.youtube.com/watch?v=le6t-kpXFZ4

float inc = 0.8;
float scl = 5;
int xcols, yrows;
Particle[] parts = new Particle[3000];
PVector[] flowField;
PVector prePos = new PVector(random(width), random(height));
int h = 1;

void setup()
{
  size(1000, 1000);
  xcols = int(width/scl);
  yrows = int(height/scl);
  colorMode(HSB);
  background(0);
  for(int i=0; i<parts.length;i++){
   parts[i] = new Particle(); 
  }
  flowField = new PVector[xcols * yrows];
  System.out.print("xcols="+xcols);
  System.out.print("yrows="+yrows);
  background(255);
}

void draw()
{
background(255);
float yoff = 0;
for (int y = 0; y < yrows;y++){
 float xoff = 0;
 for (int x = 0; x < xcols; x++){
  int index = x + y*xcols;
  float angle = noise(xoff, yoff)*TWO_PI;
  PVector vector = new PVector(0,0).fromAngle(angle).setMag(0.1);
  flowField[index] = vector;
  
   xoff += inc;
 //  stroke(1);
 //  pushMatrix();
  // translate (x*scl, y*scl);
  // rotate(vector.heading());
  // line(0,0,scl,0);
  // popMatrix();
 // fill(random(255));
 // rect(x*scl, y*scl, scl, scl);
 }
 yoff += inc;
}
for(int i = 0; i<parts.length; i++){
  parts[i].follow(flowField);
  parts[i].update();
  parts[i].show();
  parts[i].edges();

}
}


class Particle {
 PVector position = new PVector(random(width), random(height));
 PVector velocity = new PVector(0,0);
 PVector  acc = new PVector(0,0);
 PVector prePos;
// prePos = new PVector(position.x,position.y);
 int maxSpeed = 4;
 
 void update(){
  prePos = new PVector(position.x, position.y);
  position.add(velocity);
  velocity.add(acc);
  velocity.limit(maxSpeed);
  acc.mult(0);
 }
 
 void follow(PVector[] v){
  int x = floor(position.x /scl);
  int y = floor(position.y /scl);
  int index = x + y*xcols;
  PVector force = v[index];
  applyForce(force);
 } 
 void applyForce(PVector force){
   acc.add(force);
 }
 
 void show(){
   stroke(h, 120, 120, 56);
   h = h+1;
   if(h >255){
    h = 0; 
   }
   strokeWeight(2);
   fill(random(255));
   line(position.x,position.y, prePos.x, prePos.y);
   point(position.x, position.y);
   updatePrev();
 }
 
 void updatePrev() {
 prePos.x = position.x;
 prePos.y = position.y;
 }
 
 void edges(){
  if(position.x > width-0.1) position.x = 0.1;
    if(position.x < 0.1) position.x = width-0.1;
      if(position.y > height-0.1) position.y = 0.1;
        if(position.y < 0.1) position.y = height-0.1;
 }
}