title: OpenGL transform feedback definition completely inside shader
body: <p>I'm trying to get my transform feedback running. I wanted to specify my buffer layout completely from the shaders using the core 4.4 or the GL_ARB_enhanced_layouts extension using layout (xfb_offset=xx) declarers. I assumed that after declaring these in a vertex shader i can call</p>
  
  <pre><code>GLint iTransformFeedbackVars;
  glGetProgramiv(m_uProgramID, GL_TRANSFORM_FEEDBACK_VARYINGS, &amp;iTransformFeedbackVars);
  </code></pre>
  
  <p>to get the number of potential variables that want to be written to a transform feedback buffer. But my opengl keeps returning 0 for "iTransformFeedbackVars". I tried calling the above command BEFORE and AFTER linking the program.</p>
  
  <p>Am I missing something here or is it even possible to let the shader specify the variables it wants to write to and my code create the buffer(s) after the wishes of the shader?</p>