var cnt = 5; //counter to reset animation

function setup() {

  createCanvas(400, 400); //create the canvas

  background(60); //gray background

  frameRate (10); //frame rate or speed

}

​

function draw() {

  translate(width/2,width/2) //translate the canvas by half the width/height

  stroke(70) //dark line color

  strokeWeight(2);//thin lines

  y1 = random(-400,400);//random y values:

  y3 = random(-400,400);

  y2 = random(-400,400);

  y4 = random(-400,400);

  findSolution() //call the solution function

  //Only plot lines if the solution lies within the canvas:

  if(xSoln>-200 && xSoln <200 && ySoln<200 && ySoln>-200){

      line(x1,y1,x2,y2) //draw line 

      line(x3,y3,x4,y4) //draw line

  }

  //check cnt number to reset it when it hits 300

  if(cnt > 300){

    background(60);//reset canvas

    cnt = 5;//reset counter

  }

}

//function to find solution:

function findSolution(){

  m1 = (y2-y1)/(x2-x1); //find slope1

  m2 = (y3-y4)/(x3-x4);//find slope2

  b1 = (y1-m1*x1);//find y-intercept1

  b2 = (y3-m2*x3);//find y-intercept2

  xSoln = (b1-b2)/(m2-m1);//find soln x value using substitution

  ySoln = m1*xSoln+b1;//find soln y value by evaluating line equation with xSoln

  fill(random(255),random(255),random(255)); //random color for circle

  circle(xSoln,ySoln,cnt+1);//circle with size equal to count+5

  circle(xSoln,ySoln,5);//small circle to denote solution

  cnt=cnt+1;//increments counter for circles plotted

}