title: three.js - TubeGeometry + DecalGeometry on a segment of the tube
body: <p>I want to put a decal inside a segment of a tube geometry (in the backface).</p>
  
  <p>The way I do is use TubeGeometry as the decal geometry.</p>
  
  <p>This is what I have:
  <a href="https://i.stack.imgur.com/5BVUE.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/5BVUE.jpg" alt="enter image description here"></a></p>
  
  <p>And this is what I want:
  <a href="https://i.stack.imgur.com/crkjx.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/crkjx.jpg" alt="enter image description here"></a>
   <em>(bad drawing)</em></p>
  
  <p>Sample code:</p>
  
  <pre><code>//code
  var tube = new THREE.TubeGeometry(pipelineSpline, 200, 20, 20, closed2);
  
  tubeMesh = THREE.SceneUtils.createMultiMaterialObject(
         geometry, [
              material,       // a phong material
              materialInside // a material for the inside               
         ]);
  
  scene.add(tubeMesh); 
  
  var decalGeometry = new THREE.DecalGeometry(
        tubeMesh.children[0], 
        new THREE.Vector3(0,0,0),      //position
        new THREE.Vector3(0,1,0),      //direction
        new THREE.Vector3(10,10,10),   //dimensions
        new THREE.Vector3(0,0,0)       //check
      );
  </code></pre>
  
  <p>However this seems to apply a decal of the tube along all the backside geometry path. And I want it only on one part of the BackSide of the Tube on key positions.</p>
  
  <p>How can I make a localized decal in a TubeGeometry using THREE.DecalGeometry? Is it possible?</p>