Category: 01

var segs = [];
var intersections = [];
var clicked = false;
var numSegs = 12;
var lineLength = 300;
var dotSize = 20;
 
function setup() {
  angleMode(DEGREES);
  createCanvas(700, 700);
  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)]
}

let lines = [];
let slider;
let intersectionsArray = [];
let intersection = [];
 
function setup() {
  createCanvas(720, 480);
  background(255, 204, 0);
 
  slider = createSlider(12, 100, 12);
  slider.position(50, 80);
  stroke(0,0,255);
  textSize(15);
  text('click to begin', width/2,height/2);
}
 
function mousePressed(){
 
  intersectionsArray = [];
  lines = [];
  background(255, 204, 0);
  var lineNumber = slider.value();
 
  for (var i = 0; i < lineNumber; i++){
    var newLine = new Line(random(50,width-100), random(50, height-100), random(50,width-100), random(50, height-100));
    lines.push(newLine);  
  }
 
 
  for (i = 0; i < lines.length-1; i++){
   for (var j = 1; j < lines.length; j++) {
     if (lines[i] !== lines[j]){
      intersection = (intersect(lines[i].x1, lines[i].y1, lines[i].x2, lines[i].y2, lines[j].x1, lines[j].y1, lines[j].x2, lines[j].y2));
     }
     if (intersection !== false && intersectionsArray.includes(intersection) == false){
       intersectionsArray.push(intersection);
      }
     }    
  }
  fill(255,0,0,50);
  text('number of lines:', 50,70);
  text(lines.length, 170,70);
  for (let l of lines){
    l.drawLine();
  }
 
  for (i = 0; i < intersectionsArray.length; i++) {
    ellipse(intersectionsArray[i][0], intersectionsArray[i][1],15);
  }
}
 
 
class Line {
  constructor(x1, y1, x2, y2){
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
 }
  drawLine(){
    line (this.x1, this.y1, this.x2, this.y2);
  } 
}
 
 
//intersection calculations from paul bourke and leo bottaro
function intersect(x1, y1, x2, y2, x3, y3, x4, y4) {
 
  if ((x1 === x2 && y1 === y2) || (x3 === x4 && y3 === y4)) {
    return false;
	}
 
  denominator = ((y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1));
 
  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;
 
  if (ua < 0 || ua > 1 || ub < 0 || ub > 1) {
    return false;
	}
 
  let x = x1 + ua * (x2 - x1);
  let y = y1 + ua * (y2 - y1);
 
  return [x, y]
}