function CardboardUI(gl) {
  this.gl = gl;

  this.attribs = {
    position: 0
  };
  this.program = Util.linkProgram(gl, uiVS, uiFS, this.attribs);
  this.uniforms = Util.getProgramUniforms(gl, this.program);

  this.vertexBuffer = gl.createBuffer();
  this.gearOffset = 0;
  this.gearVertexCount = 0;
  this.arrowOffset = 0;
  this.arrowVertexCount = 0;

  this.projMat = new Float32Array(16);

  this.listener = null;

  this.onResize();
}
Renders the alignment line and "options" gear. It is assumed that the canvas
this is rendered into covers the entire screen (or close to it.)