title: Why does full-screen iPhone background texture need y-offset of 32 points?
body: <p>I'm using a full-screen background texture. It's stored in a 512x512 PNG file. When rendering it to the screen using glDrawTexfOES, for some reason I need to add a 32 point y-offset in order to make it align with the screen. Why?</p>
  
  <pre><code>glBindTexture(GL_TEXTURE_2D, backgroundTexture);
  int backgroundRectangle[] = { 0, 480, 320, -480 }; // Handle origin at upper left
  glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, backgroundRectangle);
  glColor4f(1, 1, 1, 1);
  glDrawTexfOES(0, 32, 1, 320, 480);
  </code></pre>