This adds a RenderEngine type to RNA, which can be subclassed in python (c++ will follow once we support subclassing there). It's very basic, but plugs into the pipeline nicely. Two example scripts: http://www.pasteall.org/6635/python http://www.pasteall.org/6636/python Issues: * Render runs in a separate thread, and there is unrestricted access, so it's possible to crash blender with unsafe access. * Save buffers and full sample are not supported yet.