live demo at NicerApp WebOS Unified Interface
single click somewhere (not on a mesh though), to go to FlyControls.
drag the mouse cursor around to change the flight trajectory.
but when you let go of the mouse button, the view will jump around. 
source-codes are at
NicerApp-WebOS-v6.y.z/NicerAppWebOS/logic.vividUserInterface/v6.y.z/3D/na3D.js at a22eceb26b29582b6430e600495f76c0ada50e4a · NicerEnterprises/NicerApp-WebOS-v6.y.z · GitHub
and
NicerApp-WebOS-v6.y.z/NicerAppWebOS/logic.vividUserInterface/v6.y.z/3D/na3D.js at e00d84f3557cbc84c5c334d9cea3766aabc0e001 · NicerEnterprises/NicerApp-WebOS-v6.y.z · GitHub
and
https://new.nicer.app/NicerAppWebOS/3rd-party/3D/libs/three.js/examples/jsm/controls/FlyControls.js
and
https://new.nicer.app/NicerAppWebOS/3rd-party/3D/libs/three.js/examples/jsm/controls/OrbitControls.js
i now use only FlyControls, and set it’s .movementSpeed to 0 when that’s above 0 and the mouse button is released, which allows for about the same functionality as OrbitControls.
but that does not mean that the jumping around of the view has ended
also, FlyControls always “wants” to move to the 0,0,0 coordinate, and that’s where i have a cube encased in a sphere, which jumps around the view in a jittering fashion when that coordinate is reached.
i could really use some help here again.
my sources are MIT-licensed and published at GitHub - NicerEnterprises/NicerApp-WebOS-v6.y.z