GimpToolGyroscope is a tool widget providing canvas interaction for
3D rotation. The widget doesn't preset a UI, but rather
facilitates panning, rotation, and zoom, by dragging the canvas, or
using the keyboard.
Rotation is expressed using yaw/pitch/roll angles (performed in
this order). A zoom factor can be specified, which affects the
magnitude of the rotation per distance traveled. The widget can
operate in inverse mode, performing an inverse transformation.
