title: Weird!! How to read mask info from an SWF file?
body: <p>recently i am research to build some tools like <a href="http://gafmedia.com/converter/" rel="nofollow noreferrer">GAF</a></p>
  
  <p>and i'm stuck by MovieClip's mask</p>
  
  <p><img src="https://i.stack.imgur.com/tPGQa.png" alt="MovieClip Structure"></p>
  
  <p>as the image you can see ,it's an very simple start masked by an rectangle.</p>
  
  <p>i try to get those mask info from code , but got nothing. i wactch the startMc from FlashBuilder,the mask info is null</p>
  
  <p><img src="https://i.stack.imgur.com/VKzQU.png" alt="enter image description here"></p>
  
  <p>but, when i export the same MovieClip by GAF tools, it's read the mask info perfectly</p>
  
  <p><img src="https://i.stack.imgur.com/kHCnb.png" alt="enter image description here"></p>
  
  <p>so, any clue how they did this? </p>
  
  <p>thanks!</p>