let lineList = [];

let lineCount = 10;

let canWidth;

let canHeight;

​

function setup() {

  canWidth = 640;

  canHeight = 480;

  createCanvas(canWidth, canHeight);

  refresh = true;

}

​

function draw() {

  if (refresh) {

    clear();

    background(39, 94, 80);

    lineList = [];

    //draw lines

    createLines(lineCount);

    //find intersections + make a firefly

    findIntersections();

    refresh = false;

  }

}

​

function mousePressed() {

  refresh = true;

}

​

function createLines(lineCount) {

  stroke(200);

  for (i = 0; i < lineCount; i++) {

    var point1 = {x: random(canWidth), y: random(canHeight)};

    var point2 = {x: random(canWidth), y: random(canHeight)};

    line(point1.x, point1.y, point2.x, point2.y);

    var newLine = {P1: point1, P2: point2};

    append(lineList, newLine);

  }

}

​

function findIntersections() {

  //variable for intersection must be initiated with some value

  var intersect = {x: 0, y: 0};

  for (i = 0; i < lineList.length; i++) {

    for (j = i + 1; j < lineList.length; j++) {

      var currentLine = lineList[i];

      var compareLine = lineList[j];

      if (getIntersection(currentLine, compareLine, intersect)) {

        noStroke();

        colorMode(RGB);

        fill(color(255,50));

        circle(intersect.x, intersect.y, 15, 120);

        fill(color(255,100));

        circle(intersect.x, intersect.y, 12, 120);

        fill(color(255));        

        circle(intersect.x, intersect.y, 7);

      }

    }

  }

}

​

function getIntersection(line1, line2, intersect) {

  //denominator should be the same for both Ua and Ub

  //(y4 - y3)(x2 - x1) - (x4 - x3)(y2 - y1)

  var denominator = (line2.P2.y - line2.P1.y) * (line1.P2.x - line1.P1.x) - (line2.P2.x - line2.P1.x) * (line1.P2.y - line1.P1.y);

  //check if lines are parallel

  if (denominator == 0) return false;

  var numerator1 = (line2.P2.x - line2.P1.x) * (line1.P1.y - line2.P1.y) - (line2.P2.y - line2.P1.y) * (line1.P1.x - line2.P1.x);

  var numerator2 = (line1.P2.x - line1.P1.x) * (line1.P1.y - line2.P1.y) - (line1.P2.y - line1.P1.y) * (line1.P1.x - line2.P1.x);

  if (Ua < 0 || Ub < 0) return false;

  var Ua = numerator1 / denominator;

  var Ub = numerator2 / denominator;

  if (Ua > 1 || Ub > 1) return false;

​

  //x = x1 + ua(x2 - x1)

  //y = y1 + ua(y2 - y1)

  intersect.x = line1.P1.x + Ua * (line1.P2.x - line1.P1.x);

  intersect.y = line1.P1.y + Ua * (line1.P2.y - line1.P1.y);

  //print("true");

  return true;

}