function find_path(level, src, dst)
  local done = initialize_array(false, lh, lw)
  local cands = {}
  table.insert(cands, {x=src.x, y=src.y})
  while #cands > 0 do
    local cand = table.remove(cands, 1)
    local x,y = cand.x, cand.y
    if x == dst.x and y == dst.y then return cand end
    if y >= 1 and y <= lh and x >= 1 and x <= lw and not done[y][x] then
      done[y][x] = true
      local curr = level[y][x]
      if curr ~= CELL_WALL and curr ~= CELL_CRATE and curr ~= CELL_CRATE_ON_TARGET then
        table.insert(cands, {x=x-1, y=y, prev=cand})
        table.insert(cands, {x=x+1, y=y, prev=cand})
        table.insert(cands, {x=x, y=y-1, prev=cand})
        table.insert(cands, {x=x, y=y+1, prev=cand})
      end end end end
function unwind_path(c)
  local result = {}
  while c do
    table.insert(result, {x=c.x, y=c.y})
    c = c.prev
  end
  return result
end
function draw_path(path)
  color(1,0,0)
  for _,cell in ipairs(path) do
    rect('line', left+(cell.x-1)*side, top+(cell.y-1)*side, side, side)
  end end
function initialize_array(val, dim, ...)
  local result = {}
  local other_dims = {...}
  if #other_dims == 0 then
    for i=1,dim do
      table.insert(result, val)
    end
  else
    for i=1,dim do
      table.insert(result, initialize_array(val, ...))
    end
  end
  return result
end

  path = unwind_path(find_path(level_state, {x=15,y=12}, {x=12, y=9}))

  draw_path(path)