Add some extra rotations and offsets, to show off the power of
what you can do with a single draw call. Also use QGLWindow instead
of QGLWidget. This improves performance from 23 FPS to 30 FPS on a
4k monitor with integrated Intel graphics.

Change-Id: Iedac1c14cc6057959aa15faaacdf29da91f36ab1
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>