Constraint Points

Hi three js community,
I want to create kind of a cropping tool on a plane. Like this one more or less

by dragging (3) I can only move the height
by dragging (4) I can move height and width

For the controllers I created meshes.
How can I constraint all the points so that for instance if I drag down (4) also (3) and the top-right-corner move down?

Something close about cropping is this topic: Capture part of scene selected with mouse - #7 by prisoner849
I didn’t get the idea of using meshes as controllers, when you can do it with js and html elements :thinking:

The idea is, that we want to still have the camera movement and rotation of the camera and so on. this could all be done with plain js/html but then we would have to map the camera movement and so on to the js/html elements, which we thought is the more tough and error prune task