// Daniel Shiffman

// http://natureofcode.com

​

// Flow Field Following

​

​

class FlowField {

​

  constructor(r) {

    // How large is each "cell" of the flow field

    this.resolution = r;

    // Determine the number of columns and rows based on sketch's width and height

    this.cols = width / this.resolution;

    this.rows = height / this.resolution;

    // A flow field is a two dimensional array of p5.Vectors

    // We can't make 2D arrays, but this is sort of faking it

    this.field = this.make2Darray(this.cols);

    this.init();

  }

​

  make2Darray(n) {

    let array = [];

    for (let i = 0; i < n; i++) {

      array[i] = [];

    }

    return array;

  }

​

  init() {

    // Reseed noise so we get a new flow field every time

    // Need to get noise working

    noiseSeed(Math.floor(random(10000)));

    let xoff = 0;

    for (let i = 0; i < this.cols; i++) {

      let yoff = 0;

      for (let j = 0; j < this.rows; j++) {

        let theta = map(noise(xoff, yoff), 0, 1, 0, TWO_PI);

        //let theta = map(sin(xoff)+cos(yoff),-2,2,0,TWO_PI);

        // Polar to cartesian coordinate transformation to get x and y components of the vector

        this.field[i][j] = createVector(cos(theta), sin(theta));

        yoff += 0.1;

      }

      xoff += 0.1;

    }

  }

​

  // Draw every vector

  display() {

    for (let i = 0; i < this.cols; i++) {

      for (let j = 0; j < this.rows; j++) {

        this.drawVector(this.field[i][j], i * this.resolution, j * this.resolution, this.resolution - 2);

      }

    }

  }

​

  lookup(lookup) {

    let column = Math.floor(constrain(lookup.x / this.resolution, 0, this.cols - 1));

    let row = Math.floor(constrain(lookup.y / this.resolution, 0, this.rows - 1));

    //println(lookup.x);

    return this.field[column][row].copy();

  }

​

  // Renders a vector object 'v' as an arrow and a location 'x,y'

  drawVector(v, x, y, scayl) {

    push();

    let arrowsize = 4;

    // Translate to location to render vector

    translate(x, y);

    stroke(0, 100);

    // Call vector heading function to get direction (note that pointing to the right is a heading of 0) and rotate

    rotate(v.heading());

    // Calculate length of vector & scale it to be bigger or smaller if necessary

    let len = v.mag() * scayl;

    // Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)

    line(0, 0, len, 0);

    //line(len,0,len-arrowsize,+arrowsize/2);

    //line(len,0,len-arrowsize,-arrowsize/2);

    pop();

  }

}