title: Casting shadow on MeshPhongMaterial or MeshLambertMaterial in Three.js
body: <p>I feel like I'm missing something simple here.</p>
  
  <p>I used <a href="http://jsfiddle.net/4Txgp/234/" rel="noreferrer">JSFiddle by @WestLangley</a>, which demonstrates how to cast a shadow from an object onto a plane.</p>
  
  <p>Everything works as expected when the plane is filled with just color:</p>
  
  <pre><code>var groundMaterial = new THREE.MeshLambertMaterial({
    color: 0xFF0000
  });
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/4WLtm.png" alt="enter image description here"></p>
  
  <p>Then I change it to use texture instead:</p>
  
  <pre><code>var groundMaterial = new THREE.MeshLambertMaterial({
    // color: 0xFF0000,
    map: texture
  });
  </code></pre>
  
  <p>..all of a sudden, shadow is gone:</p>
  
  <p><img src="https://i.stack.imgur.com/TCbKc.png" alt="enter image description here"></p>
  
  <p>This happens with both <code>MeshPhongMaterial</code> and <code>MeshLambertMaterial</code>.</p>
  
  <p>Note that neither camera position nor shadow configuration is changed. Everything stays the same, yet shadow is gone.</p>
  
  <p>Should texture be "told" to receive light or is this something else?</p>
  
  <p>Tested on r61, r66, r67.</p>