语法：

mp_grid_clear_all(id);

返回: Boolean（布尔值）

描述

With this function you can clear an mp_grid of all "forbidden" cells.

例如：

if !instance_exists(obj_Player) mp_grid_clear_all(grid);

The above code will clear the mp_grid indexed in the variable "grid", marking all the cells as free, if an instance of the object "obj_Player" no longer exists in the room.