BounceOnce

let x=0,
    y=0,
    a=100,
    b=270;
function setup() {
  createCanvas(400, 400);
  background(0);
  plotP();
}
function draw() {
  translate(15,width/2); stroke(random(50,155),random(50,255),random(50,255))
  strokeWeight(0.08);
    mBeam();
}
function mBeam(){
  if(mouseX-15>width/2-a && mouseX-15 < width-a-30){
    msX = mouseX- 15;
    msY = mouseY-width/2;
    m1 = (msY)/(msX-a);//slope
    m2 = (msY)/(msX-b);//slope2
    a1 = m1*m1;
    a2 = m2*m2;
    b1 = -(2*a*m1*m1+4*a);
    b2 = 4*a-2*b*m2*m2;
    c1 = a*a*m1*m1;
    c2 = b*b*m2*m2-4*370*a;
    tmp = (b1*b1-4*a1*c1)
    tmp2 = (b2*b2-4*a2*c2)
    x1 = (-b1-sqrt(tmp))/(2*a1);
    x2 = (-b2+sqrt(tmp2))/(2*a2);
    y1 = sqrt(4*a*x1);
    y2 = sqrt(370*4*a-4*a*x2);
    if(msY<0){
      line(msX,msY,x1,y1);
      line(msX,msY,x2,y2);
      line(x1,y1,width-x1-30,y1)
      line(x2,y2,-x2+width-30,y2)
    }
    if(msY>=0){
      line(msX,msY,x1,-y1);
      line(msX,msY,x2,-y2);
      line(x1,-y1,width-x1-30,-y1)
      line(x2,-y2,-x2+width-30,-y2)
    }
  }
}
function plotP(){
  if (x===0){translate(15,width/2)};
  for (i=-100;i<100;i=i+1){
    t=i/90;
    y=2*a*t;
    x=a*t*t;
    g =-a*t*t+370
    circle(x,y,2);
    circle(g,y,2)
    circle(b,0,10)
    circle(a,0,10);
    line(-a,-width/2,-a,width/2)
  }
}
function mousePressed(){
  background(0);
  plotP()
}