Several months ago, I was followint a random chain of Processing links, and came upon a script that created a Black and White 2D array of line segments that sort of followed the mouse pointer and made something that looked liek a magnetic field.

Do any of you remember seeing that script, and where it is?

Maybe you mean mine, I just found it in the sketchbook of Processing version 0054. It's not online, but here's the code. Warning: this is old code, so you'll need to tweak it a bit before it will run on Processing Beta. Another warning: the code is really weird, I wrote it when I just started programming.

Code:

avoidVector[][] vectors = new avoidVector[9][9];
float adjust = 0;

void setup() {
  size(200, 200);
  background(255);
  ellipseMode(CENTER_DIAMETER);
  
  for (int i = 0; i < 9; i++) {
    for (int j = 0; j < 9; j++) {
	vectors[i][j] = new avoidVector(i*20+20, j*20+20, 20);
    }
  }
}

void loop() {
  for (int i = 0; i < 9; i++) {
    for (int j = 0; j < 9; j++) {
	vectors[i][j].update();
    }
  }
  
  if (keyPressed) {adjust = PI/2;}
  if (mousePressed) {adjust = PI;}
  if (!mousePressed && !keyPressed) {adjust = 0;}
}

void vector(int x, int y, float dir, float len) {
  dir = dir - 2*dir - PI;
  float x2 = sin(dir) * len + x;
  float y2 = cos(dir) * len + y;
  line(x, y, x2, y2);
}

class avoidVector {
  int x, y;
  float len;
  
  avoidVector(int nx, int ny, float nlen) {
    x = nx;
    y = ny;
    len = nlen;
  }
  
  void update() {
    stroke(0);
    vector(x, y, atan2(mouseY-y, mouseX-x)-PI/2+adjust, len);
    
    fill(255, 0, 0);
    noStroke();
    ellipse(x, y, 4, 4);
  }    
} 

Koenie

If you are looking for the implementation of a hexagonal grid.  This can help you.

Quite a while ago, I had worked on one.  Although the code is a bit messy (it was my first Processing applet!!) hope it helps you.  It may not be the best way, I used no references at all, just a piece of paper an trigonometry.

here's the applet: Hexagonando

cheers
ricard

edit: this applet has a small bug, where the particles move out of the screen.  but I'm planning to fix these things soon when I update it to P5 BETA, now the code only works with ALPHA.