TrackballControls

Trackball camera controls matching EASEL.js r186 TrackballControls. Unlike {@link OrbitControls }, the camera up vector is not kept constant: dragging over the poles rolls the view instead of flipping it. The left, middle, and right mouse buttons rotate, zoom, and pan by default; holding one of {@link TrackballControls.keys} switches every button to that action. One finger rotates and two fingers zoom and pan. Call update() once per frame, and handleResize() whenever the element moves or changes size.