title: Dropdown UI widget for fx/hlsl shader
body: <p>I've made a HLSL shader (fx format) and would like to add a enum/list paremeter to its UI - as a better alternative to the list of boolean flags. </p>
  
  <p>So instead of :</p>
  
  <ul>
  <li>[x] "Use custom map"</li>
  <li>[x] "Use custom map alpha"</li>
  <li>[x] "Use diffuse alpha"</li>
  <li>[x] "Use specular alpha"</li>
  <li>[x] "Use normal alpha"</li>
  </ul>
  
  <p>have: </p>
  
  <ul>
  <li>Source: [ "Use custom map" ] </li>
  </ul>
  
  <p>with all 5 choices and the index to selected item on the code level.</p>
  
  <p>"DirectX Standard Annotations and Semantics Reference" mentions about the ListPicker widget but I can't find any example or description how to use it. </p>
  
  <p>The questions are:</p>
  
  <ul>
  <li>Is it possible to have a custom dropdown-like widget in the shader's UI?</li>
  <li>How to achieve it?</li>
  </ul>