dragSelection method

Implementation

void dragSelection(
  Offset delta, {
  String? eventId,
  bool isWorldDelta = false,
  bool resetUnboundOffset = false,
}) async {
  if (selectedNodeIds.isEmpty) return;

  // If the delta is not already in world coordinates,
  // convert it by dividing by the viewport zoom.
  final Offset effectiveDelta = isWorldDelta ? delta : delta / _viewportZoom;

  for (final id in selectedNodeIds) {
    final node = nodes[id]!;

    // Reset the unbound offset if requested (e.g. during undo/redo)
    if (resetUnboundOffset) {
      _unboundNodeOffsets[id] = node.offset;
    } else {
      _unboundNodeOffsets.putIfAbsent(id, () => node.offset);
    }

    // Update the unbound offset by adding the effective delta.
    _unboundNodeOffsets[id] = _unboundNodeOffsets[id]! + effectiveDelta;

    if (config.enableSnapToGrid) {
      final unboundOffset = _unboundNodeOffsets[id]!;

      // Snap the node's offset to the grid using rounding.
      node.offset = Offset(
        (unboundOffset.dx / config.snapToGridSize).round() *
            config.snapToGridSize,
        (unboundOffset.dy / config.snapToGridSize).round() *
            config.snapToGridSize,
      );
    } else {
      // Apply the effective delta directly to the node's offset.
      node.offset += effectiveDelta;
    }
  }

  linksDataDirty = true;
  nodesDataDirty = true;

  // Emit a DragSelectionEvent with the effective delta (in world coordinates).
  eventBus.emit(
    DragSelectionEvent(
      id: eventId ?? const Uuid().v4(),
      selectedNodeIds.toSet(),
      effectiveDelta,
    ),
  );
}