Method txn

src/ink/log-update.ts:765–772

(fn: (prev: Point) => [patches: Diff, next: Delta])

  }

  txn(fn: (prev: Point) => [patches: Diff, next: Delta]): void {
    const [patches, next] = fn(this.cursor)
    for (const patch of patches) {
      this.diff.push(patch)
    }
    this.cursor.x += next.dx
    this.cursor.y += next.dy
  }
}