title: glEnable(GL_DEPTH_TEST) not working?
body: <p>when I enable the lighting in the opengl es, I suddenly found the depth test fails to work. It looks some object is transparent after some rotation. Handle should be invisible from this angle.</p>
  
  <p>I am using glEnable(GL_DEPTH_TEST) in the beginning.</p>
  
  <p>I am using OpenGL ES 2.0</p>
  
  <p>Anything can be wrong?</p>
  
  <p>When I don't use light, everything looks fine.</p>
  
  <p><img src="https://i.stack.imgur.com/vOBtp.png" alt="enter image description here"></p>