Problems with noise flow field

Processing Coding Questions
1

Hello,

I try to follow the Perlin noise flow field video:

I have a weird behaviour and I don’t understand why. First, here is the code, similar to the one from the video:

flow_field file:

int cols, rows;
int scale = 20;
float inc = 0.1;
float zoff = 0;

Particles[] particle = new Particles[100];
PVector[] flowField; 

void setup()
{
     size(400, 400);
     background(255);
     cols = floor(width / scale);
    // println(cols);
     rows = floor(height / scale);
     for(int i = 0; i < particle.length; i++)
     {
        particle[i] = new Particles();
     }
  flowField = new PVector[cols*rows]; 
}

void draw()
{
    background(255);
    float yoff = 0;
    
    
    stroke(0, 50);
    
    for(int y = 0; y < rows; y++)
    {
      float xoff = 0;
       for(int x = 0; x < cols; x++)
       {
          int index = x + y * cols;
         // println(index);
          float angle = noise(xoff, yoff, zoff) * TWO_PI;
          PVector v = PVector.fromAngle(angle);
          flowField[index] = v;
          pushMatrix();
          translate(x * scale, y*scale);
          rotate(v.heading());
          strokeWeight(1);
          line(0, 0, scale, 0);
          popMatrix();
          xoff += inc;
       }
       yoff += inc;
       zoff += 0;
    }
  
  for(int i = 0; i < particle.length; i++)
  {
     particle[i].follow(flowField);
     particle[i].update();
     particle[i].display();
     particle[i].edges();
     
  }
  
}

Particles file:

class Particles
{
    PVector location;
    PVector velocity;
    PVector acceleration;

    Particles()
    {
       location = new PVector(random(width - 1), random(height - 1));
       velocity = new PVector(0, 0);
       acceleration = new PVector(0, 0);
    }
    
    void update()
    {
       location.add(velocity);
       velocity.add(acceleration);
       //velocity.limit(0.3);
       acceleration.mult(0);
    }
    
    void display()
    {
      strokeWeight(3);
      stroke(2);
      point(location.x, location.y);
      
    }
    
    void applyForce(PVector force)
    {
       acceleration.add(force); 
    }
    
    void follow(PVector[] flowField)
    {
        int x = floor(location.x / scale);
        println("X: " + x);
        int y = floor(location.y / scale);
        println("Y: " + y);
        int index = x + y * cols;
        applyForce(flowField[index]);
    }
    
    void edges()
    {
       if (location.x < 0)
       {
         location.x = width;
          //velocity.x *= -1; 
       }
       
       if (location.x > width)
       {
         location.x = 0;
          //velocity.x *= -1; 
       }
       
       if (location.y < 0)
       {
         location.y = height;
         // velocity.y *= -1; 
       }
       
       if (location.y > height)
       {
         location.y = 0;
         // velocity.y *= -1; 
       }
    }
}

Now when I run this code, it gives me ArrayIndexOutOfBoundsException when I call applyForce() function.
The problem is that indeed, the value of the index calculated is over the boundaries, but I don’t understand why on the Particles file is calculating wrong and inside the flow_field file, is calculating correctly ?

Hope you can help me to clarify this. :slight_smile: