var x = 180;

var y = 148;

// coordinates for rainbow exit

var xr, yr;

// coordinates of the verteces of the triangle

var xb1 = 150;

var yb1 = 200;

var xb2 = 200;

var yb2 = 113;

var xb3 = 250;

var yb3 = 200;

// color array for rainbow colors

var c = [];

var d;

​

function setup() {

  createCanvas(400, 400);

  c = ['red','red','orange','orange','yellow','yellow','yellow','green','green','blue','blue','blue','purple','purple'];

    d = color(random(50,255),random(50,255),random(50,255),random(100,255));

}

​

function draw() {

  background(0);

  // draw triangle

  stroke(d);

  strokeWeight(5);

  fill(0,0,0,100);

  triangle(xb1,yb1,xb3,yb3,xb2,yb2);

  // draw light ray

  stroke(255,255,255,230);

  strokeWeight(2);

  if (mouseX > xb1 && mouseX < xb2 && mouseY < yb1 && mouseY > yb2) {

    // change point of refraction

    y = mouseY;

    x = (y-yb1)*(xb2-xb1)/(yb2-yb1)+xb1;

  };

  line(0,200,x,y);

  // draw light refracting inside prism

  for(var i = 0; i < 14; i++) {

    if (mouseX == 0 && mouseY == 0) {

      yr = y-6;

      print("I'm off the screen");

    }

    if (mouseX > xb1 && mouseX < xb2 && mouseY < yb1-5 && mouseY > yb2+5) {

      // change point of refraction

      yr = mouseY-6;

    }

    else {

    };

    xr = (yr+i-yb2)*(xb2-xb3)/(yb2-yb3)+xb2;

    strokeWeight(.3);

    line(x,y,xr,yr+i);

    strokeWeight(2);

    stroke(c[(i+mouseY)%14]);

    line(xr,yr+i,width,yr+20+i*1.5);

  }

}