title: OpenGL read pixels faster than glReadPixels
body: <p>Is there a way to increase the speed of <code>glReadPixels</code>? Currently I do:</p>
  <pre><code>Gdx.gl.glReadPixels(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight(), GL20.GL_RGBA, GL20.GL_UNSIGNED_BYTE, pixels);
  </code></pre>
  <p>The problem is that it blocks the rendering and is slow.</p>
  <p>I have heard of Pixel Buffer Objects, but I am quite unsure on how to wire it up and whether it is faster or not.</p>
  <p>Also is there any other solutation than <code>glReadPixels</code>?</p>
  <p>Basically, I want to take a screenshot as fast as possible, without blocking the drawing of the next scene.</p>