rune.js

var r = new Rune({
  container: "#canvas",
  width: 800,
  height: 600,
  debug: true
});

var x = 0;
var y = 0;
var h = 300;

var right = r.group(400, 100);
for(var i = 0; i < 20; i++) {
  r.line(x, y, x, y + h, right)
    .strokeWidth(5)
  x += 20 - i;
  y += (20 - i) / 4;
  h -= (20 - i) / 2;
}

r.draw();