clamp

clamp(v, lo, hi) -> int

Constrains a value to a range: it returns lo if v is below the range, hi if it is above, and v unchanged when it already lies within [lo, hi]. The classic use is keeping a moving object on screen or inside a grid, so its position can never run past the walls no matter how fast it moves. It saves you writing a pair of if checks by hand. Make sure lo is not greater than hi.

Parameters

vthe value to constrain

lothe lowest allowed value (inclusive)

hithe highest allowed value (inclusive)

Example

program ClampToGrid {
  property Position { column: int = 0, row: int = 0 }
  model Player { Position }

  const GRID_WIDTH: int = 20
  const GRID_HEIGHT: int = 15
  const TILE_SIZE: int = 16

  handler SpawnPlayer phase Start {
    spawn Player { Position { column: 5, row: 5 } }
  }

  handler ReadInput phase Input {
    let pressed = Input.key()
    for (Position) in query [Position, {Player}] {
      if pressed == 'd' { Position.column = Position.column + 1 }
      if pressed == 'a' { Position.column = Position.column - 1 }
      Position.column = clamp(Position.column, 0, GRID_WIDTH - 1)
    }
  }

  handler DrawWorld phase Render {
    Screen.clear(Color.MidnightBlue)
    for (Position) in query [Position, {Player}] {
      Screen.fill_rectangle(
        x: Position.column * TILE_SIZE,
        y: Position.row * TILE_SIZE,
        width: TILE_SIZE,
        height: TILE_SIZE,
        color: Color.LimeGreen)
    }
    Screen.show()
  }
}

← All symbols