title: Cube map distorts when you translate mesh
body: <p>Trying to create a skybox using the cubemap shader (like in the examples) and noticed a distortion when you transate the mesh.</p>
  
  <p>If you create a cube of say 1 dimension width, height, and depth. Set the side to be THREE.BackSide and depthWrite to false. Then scale the mesh to say 1000 units in the x, y, and z fields. </p>
  
  <p>When the mesh is positioned in the center of the world everything is fine. But as soon as you translate the mesh the cube map starts to distort badly. </p>
  
  <p><img src="https://i.stack.imgur.com/7EpmB.png" alt="enter image description here"></p>
  
  <p>You would want to move the mesh to be the same position as the camera thereby never allowing the skybox to reach its limits if the user walks around.</p>
  
  <p>The shader code I'm using is this:</p>
  
  <pre><code>'cube': {
  
      uniforms: { "tCube": { type: "t", value: null },
                  "tFlip": { type: "f", value: -1 } },
  
      vertexShader: [
  
          "varying vec3 vWorldPosition;",
  
          "void main() {",
  
              "vec4 worldPosition = modelMatrix * vec4( position, 1.0 );",
              "vWorldPosition = worldPosition.xyz;",
  
              "gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
  
          "}"
  
      ].join("\n"),
  
      fragmentShader: [
  
          "uniform samplerCube tCube;",
          "uniform float tFlip;",
  
          "varying vec3 vWorldPosition;",
  
          "void main() {",
  
              "gl_FragColor = textureCube( tCube, vec3( tFlip * vWorldPosition.x, vWorldPosition.yz ) );",
  
          "}"
  
      ].join("\n")
  
  }
  </code></pre>
  
  <p>Does anyone know if the shader can be modified to prevent this distortion?</p>
  
  <p>Many thanks!</p>