I'm trying to make the renderer write on top of the previous frame. If I understand the context of autoClear correct, renderer.autoClear = false; should make this possible, however I can't seem to make it work.
Here is a codepen example: http://codepen.io/anon/pen/ifLEz?editors=001
renderer.autoClear = false;
If I'm missing a point, feel free to fork it and paste the solution :)