///| HeightGrid — 高さ付き2Dグリッド（クォータービュー用）
pub(all) struct HeightGrid {
  width : Int
  height : Int
  cells : Array[Tile]
  heights : Array[Int]
  max_height : Int
}

///|
pub fn HeightGrid::make(
  width : Int,
  height : Int,
  fill : Tile,
  max_height : Int
) -> HeightGrid {
  let size = width * height
  {
    width,
    height,
    cells: Array::make(size, fill),
    heights: Array::make(size, 0),
    max_height,
  }
}

///|
pub fn HeightGrid::in_bounds(self : HeightGrid, x : Int, y : Int) -> Bool {
  x >= 0 && x < self.width && y >= 0 && y < self.height
}

///|
pub fn HeightGrid::get(self : HeightGrid, x : Int, y : Int) -> Tile {
  self.cells[y * self.width + x]
}

///|
pub fn HeightGrid::set(
  self : HeightGrid,
  x : Int,
  y : Int,
  tile : Tile
) -> Unit {
  self.cells[y * self.width + x] = tile
}

///|
pub fn HeightGrid::get_height(self : HeightGrid, x : Int, y : Int) -> Int {
  self.heights[y * self.width + x]
}

///|
pub fn HeightGrid::set_height(
  self : HeightGrid,
  x : Int,
  y : Int,
  h : Int
) -> Unit {
  self.heights[y * self.width + x] = h
}

///|
pub fn HeightGrid::to_ascii(self : HeightGrid) -> String {
  let buf = StringBuilder::new()
  for y in 0.. Grid2D {
  let grid = Grid2D::make(self.width, self.height, Wall)
  for y in 0..