thabir – Intersections

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//Credit to Paul Bourke for the math behind this algorithm
//Credit to Joyce for the idea of drawing the circles behind the lines
 
var num_Lines = 12;
var line_Length = 250;
var lines = [];
var intersections;
 
function calculateIntersections(i) {
  for(var j=0; j<i; j++) {
    var x1 = lines[i][0];
    var y1 = lines[i][1];
    var x2 = lines[i][2];
    var y2 = lines[i][3];
    var x3 = lines[j][0];
    var y3 = lines[j][1];
    var x4 = lines[j][2];
    var y4 = lines[j][3];
 
    var denom = ((y4 - y3)*(x2 - x1)) - ((x4 - x3)*(y2 - y1));
    var u1num = ((x4 - x3)*(y1 - y3)) - ((y4 - y3)*(x1 - x3));
    var u2num = ((x2 - x1)*(y1 - y3)) - ((y2 - y1)*(x1 - x3));
 
    if(denom!=0 && u1num!=0 && u2num!=0) {
      var u1 = (u1num*1.0) / denom;
      var u2 = (u2num*1.0) / denom;
      if(0<=u1 && u1<=1 && 0<=u2 && u2<=1) {
        var x = round(x1 + (u1*(x2 - x1)));
        var y = round(y1 + (u1*(y2 - y1)));
        intersections = append(intersections, x);
        intersections = append(intersections, y);
      }
    }
  }
}
 
function drawLinesAndCircles() {
  strokeWeight(1.5);
  fill(50, 255, 255, 50);
  for(var i=0; i<intersections.length; i+=2) {
    ellipse(intersections[i], intersections[i+1], 30, 30);
  }
  for(var i=0; i<num_Lines; i++) {
    line(lines[i][0], lines[i][1], lines[i][2], lines[i][3]);
  }
}
 
function generateRandomLines() {
  intersections = [];
  for(var i=0; i<num_Lines; i++) { lines[i] = []; lines[i][0] = floor(random(720)); lines[i][1] = floor(random(480)); do { var angle = radians(random(360)); lines[i][2] = round(cos(angle)*line_Length) + lines[i][0]; lines[i][3] = round(sin(angle)*line_Length) + lines[i][1]; } while(0>lines[i][2] || lines[i][2]>720 || 0>lines[i][3] || lines[i][3]>480);
    calculateIntersections(i);
  }
}
 
function setup() {
  createCanvas(720, 480);
  background(255, 245, 245);
  generateRandomLines();
  drawLinesAndCircles();
}
 
function draw(){
  background(255, 245, 245);
  drawLinesAndCircles();
}
 
function mousePressed() {
  background(255, 245, 245);
  generateRandomLines();
  drawLinesAndCircles();
}

 

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