Intersections

var segs = [];

var intersections = [];

var clicked = false;

var numSegs = 12;

var lineLength = 300;

var dotSize = 20;

​

function setup() {

  angleMode(DEGREES);

  createCanvas(400, 400);

  resetLines();

  findIntersections();

}

function draw() {

  background(255);

  //creates a new set of segments if the mouse is clicked

  if(clicked){

    resetLines();

    findIntersections();

    clicked = false;

  }

  drawSegs();

  drawIntersections();

}

​

function drawSegs(){

  for(i = 0; i < numSegs; i++){

    segs[i].drawSeg();

  }

}

​

function drawIntersections(){

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

    intersections[i].drawIntersection();

  }

}

function mousePressed() {

  clicked = true;

}

​

function Segment(x1, x2, y1, y2){

  this.x1 = x1;

  this.x2 = x2;

  this.y1 = y1;

  this.y2 = y2;

  this.drawSeg = function(){

    stroke(0);

    strokeWeight(2);

    line(this.x1, this.y1, this.x2, this.y2);

  }

}

​

function Intersection(x, y){

  this.xPos = x;

  this.yPos = y;

  this.drawIntersection = function(){

    strokeWeight(0);

    fill(0, 100);

    ellipse(this.xPos, this.yPos, dotSize, dotSize);

  }

}

​

function resetLines(){

  segs = [];

  for(i = 0; i < numSegs; i++){

    var x1 = random(0, width);

    var y1 = random(0, height);

    var secondPoint = setSecondPoint(x1, y1);

    var x2 = secondPoint[0];

    var y2 = secondPoint[1];  

    newSeg = new Segment(x1, x2, y1, y2);

    segs.push(newSeg);

  }

}

​

//Calculates the second point by selecting a point at the edge of a circle

//where the radius is the desired length of the lines and the center

//is the first point

function setSecondPoint(x1, y1){

  var angle = random(0, 360);

  var y2 = sin(angle) * lineLength + y1;

  var x2 = cos(angle) * lineLength + x1; 

  //If the second point is outside the canvas, another one is calculated

  while(x2 < 0 || x2 >= width || y2 < 0 || y2 >= height){

    angle = random(0, 360);

    y2 = sin(angle) * lineLength + y1;

    x2 = cos(angle) * lineLength + x1; 

  }

​

  return [x2, y2];

}

​

//iterates through all of the segments to find the intersections

function findIntersections(){

  intersections = [];

  for(firstInd = 0; firstInd < numSegs; firstInd++){

    firstSeg = segs[firstInd];

    for(secInd = 0; secInd < numSegs; secInd++){

      secondSeg = segs[secInd];

      intersection = findIntersection(firstSeg.x1, firstSeg.y1, 

                                      firstSeg.x2, firstSeg.y2,

                                      secondSeg.x1, secondSeg.y1,

                                      secondSeg.x2, secondSeg.y2);

      if(intersectionIsValid(intersection)){

        intersections.push(new Intersection(intersection[0], intersection[1]));

      }

    }

  }

}

​

//check that the intersection exists and hasn't already been discovered

function intersectionIsValid(intersection){

  if(intersection == false){

    return false;

  }

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

    if(intersections[i].xPos == intersection[0] && intersections[i].yPos == intersection[1]){

      return false;

    }

  }

  return true;

}

​

//Paul Bourke's equation for finding the intersection of two lines

//Code courtesy of Leo Bottaro

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

  // Check if none of the lines are of length 0

  if ((x1 === x2 && y1 === y2) || (x3 === x4 && y3 === y4)) {

    return false

  }

​

  denominator = ((y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1))

​

  // Lines are parallel

  if (denominator === 0) {

    return false

  }

​

  let ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3)) / denominator

  let ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3)) / denominator

​

  // is the intersection along the segments

  if (ua < 0 || ua > 1 || ub < 0 || ub > 1) {

    return false

  }

​

  // Return a object with the x and y coordinates of the intersection

  let x = x1 + ua * (x2 - x1)

  let y = y1 + ua * (y2 - y1)

​

  return [floor(x), floor(y)]

}