Intersections

    var n = 100; // number of lines

var length = 300;

var windowLength = 720;

var widnowHeight = 480;

var radius = 20;

​

function getLine(x, y, angle) {

  // compute halfways

  var distX = sin(angle) * length/2;

  var distY = cos(angle) * length/2;

  return [x - distX, y - distY, x + distX, y + distY];

}

​

// using Paul Bourke's methodology

function intersection(x1,y1, x2,y2, x3,y3, x4,y4) {

  // find denominator

  var sd = (y4 - y3)*(x2 - x1)-(x4 - x3)*(y2 - y1);

  if (sd == 0) return [-1, -1];

  var sn = (x4 - x3)*(y1 - y3)-(y4 - y3)*(x1 - x3);

  var s = sn/sd;

  // first intersection point

  var x = x1 + s*(x2 - x1);

  var y = y1 + s*(y2 - y1);

  // determine if point is within bounds (using x)

  // not using y because sin/cos work weirdly for it

  if (x >= x1 && x <= x2 && x >= x3 && x <= x4)

    return [x, y];

  // no intersection

  return [-1, -1];

}

function click() {

  // reset background

  background('#fff2f2');

  // save lines

  var lineArray = [];

  // generate n random lines, each of length 2 inches (black)

  for (var i = 0; i < n; i++) {

    var angle = random(0, PI);

    var x = random(0, windowLength);

    var y = random(0, windowHeight);

    var l = getLine(x, y, angle);

    append(lineArray, l);

  }

  // draw intersections

  fill(255, 150, 150, 50);

  strokeWeight(0);

  for (var i = 0; i < n; i++) {

    var line1 = lineArray[i];

    for (var j = i+1; j < n; j++) {

      var line2 = lineArray[j];

      var inter = intersection(line1[0], line1[1], 

        line1[2], line1[3], line2[0], 

        line2[1], line2[2], line2[3]);

      if (inter[0] > -1) 

        ellipse(inter[0], inter[1], radius);

    }

  }

  // draw lines

  strokeWeight(2);

  for (var i = 0; i < n; i++) {

    var l = lineArray[i];

    line(l[0], l[1], l[2], l[3]);

  }

  // done

}

​

function draw() { 

  if (mouseIsPressed) click();

}

​

function setup() {

  createCanvas(windowLength, windowHeight);

    background('#fff2f2');

  stroke('#000000');

}