Attachment point in dragged-object local space. Set once at drag start; the handler mutates this Vector3 in-place so updates are reflected automatically.
ReadonlyplanePlane to project the grabbed point onto. Typically the strategy's fixed drag plane.
Grid snap resolution on the plane. 0 = projection only, no snapping.
Modifies followObject in-place. Invoked after position is resolved each frame.
Called once at drag start and again whenever the drag context resets (e.g. multi-touch → single-pointer transition). Capture any object snapshot (position, rotation, scale) you need to hold fixed during the drag. Constraints that need no dynamic initialization may omit this method.
Projects the grabbed attachment point back onto a plane after position is resolved, with optional grid snapping on that plane. Owned by the strategy that requires plane-clamping (e.g. XZPlaneDragStrategy).