title: renderscript: accessing 'z' coordinate
body: <p>I'm trying to write a simple kernel for image processing; I was planning on storing the channel of image in the 'z' coordinate of an allocation.  I think this should be possible based on the <a href="http://developer.android.com/guide/topics/renderscript/compute.html" rel="nofollow">documentation</a>:</p>
  
  <blockquote>
    <p>A kernel may access the coordinates of the current execution using the x, y, and z arguments. These arguments are optional, but the type of the coordinate arguments must be uint32_t.</p>
  </blockquote>
  
  <p>I tried to write an empty kernel which uses the 'z' coordinate:</p>
  
  <pre><code>#pragma version(1)
  #pragma rs java_package_name(org.rjpower.testcompute)
  
  rs_allocation data_in;
  rs_allocation data_out;
  
  void root(const float* src, float* dst, uint32_t x, uint32_t y, uint32_t z) {
  }
  </code></pre>
  
  <p>But the compile fails with:</p>
  
  <blockquote>
    <p>error: Unexpected kernel root() parameter 'z' of type 'uint32_t'</p>
  </blockquote>
  
  <p>Are z-coordinates actually supported?</p>