title: What does glUseProgram(0) do?
body: <p><a href="https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glUseProgram.xhtml" rel="nofollow noreferrer">The OpenGL docs for <code>glUseProgram</code></a> claim that calling it with an argument of <em>zero</em> will cause the results of shader execution to be <code>undefined</code>.</p>
  <p>However, after a little searching I've seen a couple examples of people using <code>glUseProgram</code> to <em>uninstall</em> the current shader program.</p>
  <p>Is this behavior reliable? If not, then what exactly does <code>glUseProgram(0)</code> do?</p>