getFlipSlideDeltaNid method
Internal-use-only: FLIP-only Y slide delta for the live nid,
EXCLUDING any held make-room preview offset. 0.0 when no FLIP slide
is in flight for nid.
GHOST-LIFECYCLE READ. Not for painted positions: painted position is
structural + FLIP + preview, which is getSlideDeltaNid, and every
paint, hit-test, snapshot and overreach site must keep using that.
This exists for the one question that is genuinely FLIP-only:
whether an edge ghost still has a slide to animate. A ghost is an
artifact of a FLIP slide (_ghost_registry.dart), so a ghost whose
FLIP delta has reached zero is settled and must retire even while a
preview holds a non-zero offset on the same row. Reading the
composed delta there retained ghosts for the whole of a drag, which
forced every drop-target lookup onto the O(N) full scan
(RenderSliverTree.findRowAtPaintedY).
No X counterpart is needed: getSlideDeltaXNid is already FLIP-only because previews are Y offsets.
Implementation
double getFlipSlideDeltaNid(int nid) => _slide.deltaForNid(nid);