グループの子要素の位置を再帰的に更新

code:ts

// 位置の変更差分を子供全てに適用する

const updatePosition = <T extends StateItem>(item: T, diff: paper.Point): T => {

const newPosition = item.position.add(diff);

if (isGroupStateItem(item)) {

const newChildren = item.items.map((x) => (updatePosition(x, diff)))

return {

...item,

position: newPosition,

nameplate: updatePosition(item.nameplate, diff),

items: newChildren,

}

} else {

return {

...item, position: newPosition

}

}

}