qlinear expression function

Channel segment function: uses quaternions to interpolate.

A channel expression function which uses quaternions to interpolate between the keyframed values. This function requires that it has two neighboring channels named appropriately. This means they should end with x, y, and z, or be three consecutive numbers starting from 0 (such as 0, 1, 2, or 6, 7, 8).

Because the interpolation is done in quaternion space, the orientations will blend smoothly with no gimbal lock or unexpected spins. However, the rotation values may appear to jump suddenly. This is because different rotation values can represent the same orientation.

Note in the graph editor a segment using this expression will show as a dashed straight line. This does not represent the actual intermediate channel values, but does give an accurate visual feel for the behavior of the interpolation.