A-frame: How to render 2nd camera to canvas

I have a scene with two cameras - a primary camera and plan view camera. How can I render the plan view camera to a plane attached to the primary camera?

I understand that I need to attach a draw-canvas component to the plane as outlined in the Aframe docs - https://aframe.io/docs/0.5.0/components/material.html#canvas-textures. Yet this is as far as I can get with it.

<script>
  AFRAME.registerComponent('draw-canvas', {
  schema: {default: ''},

  init: function () {
    this.canvas = document.getElementById(this.data);
    this.ctx = this.canvas.getContext('2d');

    // Draw on canvas...
   }
  });
</script>

Is there a working example on how to render a camera to a canvas texture with Aframe?

Please see my demo - https://codepen.io/MannyMeadows/pen/OgxwGm

Solution

I found a spectator component to resolve this...

AFRAME.registerComponent('spectator', {
  'schema': {
    canvas: {
      type: 'string',
      default: ''
    },
    // desired FPS of spectator dislay
    fps: {
      type: 'number',
      default: '10.0'
    }
  },
  'init': function() {
    var targetEl = document.querySelector(this.data.canvas);

    this.counter = 0;
    this.renderer = new THREE.WebGLRenderer({
      antialias: false,
      alpha: true
    });

    this.renderer.setPixelRatio(window.devicePixelRatio);
    this.el.object3DMap.camera.aspect = 1;
    this.el.object3DMap.camera.updateProjectionMatrix()
    this.renderer.setSize(targetEl.offsetWidth, targetEl.offsetHeight);

    // creates spectator canvas
    targetEl.appendChild(this.renderer.domElement);
  },
  'tick': function(time, timeDelta) {

    var loopFPS = 1000.0 / timeDelta;
    var hmdIsXFasterThanDesiredFPS = loopFPS / this.data.fps;
    var renderEveryNthFrame = Math.round(hmdIsXFasterThanDesiredFPS);

    if (this.counter % renderEveryNthFrame === 0) {
      this.render(timeDelta);
    }
    this.counter += 1;
  },
  'render': function() {
    this.renderer.render(this.el.sceneEl.object3D, this.el.object3DMap.camera);
  }
});

.container {
  position: absolute;
  width: 300px;
  height: 300px;
  top: 10px;
  z-index: 3;
  right: 20px;
}

<html>

<head>
  <script src="https://aframe.io/releases/0.6.0/aframe.min.js"></script>
  <script src="//cdn.rawgit.com/donmccurdy/aframe-extras/v3.8.5/dist/aframe-extras.min.js"></script>
</head>

<body>
  <a-scene stats>
    <a-assets>
      <img id="map-tex" src="https://cdn0.iconfinder.com/data/icons/architecture-construction/128/1-512.png" crossorigin>
    </a-assets>
    <!-- Scene geometry -->
    <a-sphere position="0 1.25 -1" radius="1.25" color="#EF2D5E">
    </a-sphere>
    <a-box position="-1 0.5 1" rotation="0 45 0" width="1" height="1" depth="1" color="#4CC3D9"></a-box>
    <a-cylinder position="1 0.75 1" radius="0.5" height="1.5" color="#FFC65D"></a-cylinder>
    <a-plane rotation="-90 0 0" width="4" height="4" color="#7BC8A4"></a-plane>
    <a-sky color="#ECECEC"></a-sky>
    <!-- 1st person camera -->
    <a-entity>
      <a-camera id="primaryCamera" position="0 0 3">
      </a-camera>
      <a-camera position="0 20 3" active="false">
        <a-sphere id="icon" position="0 0 0" radius="0.1" color="#EF2D5E"></a-sphere>
      </a-camera>
    </a-entity>
    <!-- spectator camera -->
    <a-entity camera="active:false; fov:1; far:280" spectator="canvas:#spectatorDiv;" active="false" look-controls="enabled: false" wasd-controls="enabled: false" id="secondaryCamera" position="0 300 0" rotation="-90 0 0">
    </a-entity>
    <!-- mini-map -->
    <a-plane position="0 21 0" rotation="-90 0 0" width="4" height="4" src="#map-tex"></a-plane>
  </a-scene>
  <div class="container" id="spectatorDiv">
  </div>
</body>

</html>