RedMew/map_gen/misc/rail_grid.lua

local Event = require "utils.event"

mymodule = {}

local function rot_pos(pos, rot)
  local ctr = {x = 15, y = 15}
  return {
    x = ctr.x + (pos.x - ctr.x) * rot.x - (pos.y - ctr.y) * rot.y,
    y = ctr.y + (pos.x - ctr.x) * rot.y + (pos.y - ctr.y) * rot.x
  }
end

local function rot_dir(dir, rot)
  local cnt = 2 * math.atan2(rot.y, rot.x) / math.pi
  return (dir + 2 * cnt) % 8
end

local rail_grid = {
  ["allway"] = {{["name"] = "curved-rail", ["position"] = {["x"] = 10, ["y"] = 4}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 1}, ["direction"] = 0}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 12.5, ["y"] = 0.5}, ["direction"] = 4}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 17.5, ["y"] = 0.5}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 1}, ["direction"] = 0}, {["name"] = "curved-rail", ["position"] = {["x"] = 20, ["y"] = 4}, ["direction"] = 4}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 3}, ["direction"] = 0}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 15, ["y"] = 3}, ["direction"] = 0}, {["name"] = "curved-rail", ["position"] = {["x"] = 20, ["y"] = 6}, ["direction"] = 4}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 3}, ["direction"] = 0}, {["name"] = "curved-rail", ["position"] = {["x"] = 12, ["y"] = 6}, ["direction"] = 6}, {["name"] = "curved-rail", ["position"] = {["x"] = 12, ["y"] = 8}, ["direction"] = 4}, {["name"] = "curved-rail", ["position"] = {["x"] = 18, ["y"] = 8}, ["direction"] = 5}, {["name"] = "curved-rail", ["position"] = {["x"] = 20, ["y"] = 6}, ["direction"] = 3}, {["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 10}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 6, ["y"] = 10}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 6, ["y"] = 10}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 7}, ["direction"] = 3}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 15.5, ["y"] = 6.5}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 7}, ["direction"] = 5}, {["name"] = "curved-rail", ["position"] = {["x"] = 26, ["y"] = 10}, ["direction"] = 7}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 15.5, ["y"] = 9.5}, ["direction"] = 1}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 14.5, ["y"] = 9.5}, ["direction"] = 3}, {["name"] = "curved-rail", ["position"] = {["x"] = 24, ["y"] = 12}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 11}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 8, ["y"] = 12}, ["direction"] = 3}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 13}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 11}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 13}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 11}, ["direction"] = 3}, {["name"] = "curved-rail", ["position"] = {["x"] = 22, ["y"] = 12}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 27, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 29, ["y"] = 11}, ["direction"] = 2}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 0.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 15}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 15}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 13}, ["direction"] = 3}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 12.5, ["y"] = 12.5}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 17, ["y"] = 13}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 15}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 17, ["y"] = 15}, ["direction"] = 1}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 17.5, ["y"] = 12.5}, ["direction"] = 3}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 29.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 3, ["y"] = 15}, ["direction"] = 0}, {["na
  ["tshape"] = {{["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 12}, ["direction"] = 3}, {["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 5, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 17, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 21, ["y"] = 11}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 26, ["y"] = 12}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 25, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 27, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 29, ["y"] = 11}, ["direction"] = 2}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 0.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 7.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 15}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 15}, ["direction"] = 7}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 22.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 29.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 3, ["y"] = 15}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 15}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 17}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 21, ["y"] = 17}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 21, ["y"] = 15}, ["direction"] = 3}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 27, ["y"] = 15}, ["direction"] = 0}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 0.5, ["y"] = 17.5}, ["direction"] = 2}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 7.5, ["y"] = 17.5}, ["direction"] = 2}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 8.5, ["y"] = 17.5}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 17}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 19}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 19}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 17}, ["direction"] = 3}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 21.5, ["y"] = 17.5}, ["direction"] = 5}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 22.5, ["y"] = 17.5}, ["direction"] = 2}, {["name"] = "rail-chain-signal", ["position"] = {["x"] = 29.5, ["y"] = 17.5}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 19}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 20}, ["direction"] = 3}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 5, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, [
  ["straight"] = {{["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 5, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 17, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 21, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 25, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 27, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 29, ["y"] = 11}, ["direction"] = 2}, {["name"] = "rail-signal", ["position"] = {["x"] = 1.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 3, ["y"] = 15}, ["direction"] = 0}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 27, ["y"] = 15}, ["direction"] = 0}, {["name"] = "rail-signal", ["position"] = {["x"] = 28.5, ["y"] = 17.5}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 5, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 17, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 21, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 25, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 27, ["y"] = 19}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 29, ["y"] = 19}, ["direction"] = 2}},
  ["corner"] = {{["name"] = "straight-rail", ["position"] = {["x"] = 1, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 3, ["y"] = 11}, ["direction"] = 2}, {["name"] = "curved-rail", ["position"] = {["x"] = 8, ["y"] = 12}, ["direction"] = 3}, {["name"] = "rail-signal", ["position"] = {["x"] = 1.5, ["y"] = 12.5}, ["direction"] = 6}, {["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 15}, ["direction"] = 1}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 3, ["y"] = 15}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 15}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 13, ["y"] = 17}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 17}, ["direction"] = 5}, {["name"] = "straight-rail", ["position"] = {["x"] = 15, ["y"] = 19}, ["direction"] = 1}, {["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 20}, ["direction"] = 3}, {["name"] = "curved-rail", ["position"] = {["x"] = 18, ["y"] = 22}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 23}, ["direction"] = 1}, {["name"] = "curved-rail", ["position"] = {["x"] = 10, ["y"] = 26}, ["direction"] = 0}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 15, ["y"] = 27}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 27}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 29}, ["direction"] = 0}},
  ["ushape"] = {{["name"] = "curved-rail", ["position"] = {["x"] = 12, ["y"] = 4}, ["direction"] = 6}, {["name"] = "curved-rail", ["position"] = {["x"] = 20, ["y"] = 4}, ["direction"] = 3}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 7}, ["direction"] = 7}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 7}, ["direction"] = 1}, {["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 10}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 7}, ["direction"] = 3}, {["name"] = "curved-rail", ["position"] = {["x"] = 26, ["y"] = 10}, ["direction"] = 0}, {["name"] = "rail-signal", ["position"] = {["x"] = 7.5, ["y"] = 9.5}, ["direction"] = 5}, {["name"] = "big-electric-pole", ["position"] = {["x"] = 3, ["y"] = 15}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 27, ["y"] = 15}, ["direction"] = 0}, {["name"] = "curved-rail", ["position"] = {["x"] = 26, ["y"] = 20}, ["direction"] = 5}, {["name"] = "curved-rail", ["position"] = {["x"] = 4, ["y"] = 20}, ["direction"] = 3}, {["name"] = "straight-rail", ["position"] = {["x"] = 7, ["y"] = 23}, ["direction"] = 1}, {["name"] = "straight-rail", ["position"] = {["x"] = 9, ["y"] = 23}, ["direction"] = 5}, {["name"] = "curved-rail", ["position"] = {["x"] = 12, ["y"] = 26}, ["direction"] = 7}, {["name"] = "curved-rail", ["position"] = {["x"] = 20, ["y"] = 26}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 23, ["y"] = 23}, ["direction"] = 3}, {["name"] = "train-stop", ["position"] = {["x"] = 25, ["y"] = 15}, ["direction"] = 4}}
}

local paddings = {
  [2] = {{["name"] = "straight-rail", ["position"] = {["x"] = 31, ["y"] = 11}, ["direction"] = 2}, {["name"] = "straight-rail", ["position"] = {["x"] = 31, ["y"] = 19}, ["direction"] = 2}},
  [4] = {{["name"] = "straight-rail", ["position"] = {["x"] = 11, ["y"] = 31}, ["direction"] = 0}, {["name"] = "straight-rail", ["position"] = {["x"] = 19, ["y"] = 31}, ["direction"] = 0}}
}


local function tbl2key(tbl)
	return tbl[1] .. "," .. tbl[2]
end

local cities = {
	[tbl2key({6, -8})] = "Edinburgh Waverley",
	[tbl2key({11, 0})] = "Newcastle Central",
	[tbl2key({4, 9})] = "Liverpool Lime Street",
	[tbl2key({9, 15})] = "Birmingham New Street",
	[tbl2key({15, 21})] = "London Euston",
	[tbl2key({4, 21})] = "Bristol Temple Meads",
	[tbl2key({16, 15})] = "Cambridge",
}

local function connect_line(s, e)
	local bitmap = global.bitmap
	for i = s[1], e[1] do
		if global.bitmap[i] == nil then
			bitmap[i] = {}
		end
		bitmap[i][s[2]] = 1
	end
	for j = s[2], e[2] do
		if bitmap[e[1]] == nil then
			bitmap[e[1]] = {}
		end
		bitmap[e[1]][j] = 1
	end
end

local function on_init()
	global.bitmap = {}
	connect_line({  6,  -8}, {  6,   0})
	connect_line({  6,   0}, { 11,   0})
	connect_line({  9,   0}, {  9,   9})
	connect_line({  4,   9}, { 12,   9})
	connect_line({  9,  15}, { 16,  15})
	connect_line({ 12,   9}, { 12,  21})
	connect_line({  4,  21}, { 15,  21})
end

Event.on_init(on_init)

local function build_intersection(type, origin, rot)
  local surface = game.surfaces[1]
  for _, v in pairs(rail_grid[type]) do
    local pos = rot_pos(v.position, rot)
    local dir = rot_dir(v.direction, rot)
    local ety = surface.create_entity{name=v.name, position={origin.x + pos.x, origin.y + pos.y}, force="neutral", direction=dir}
	if v.name == "train-stop" then
		ety.backer_name = cities[tbl2key({origin.x/32, origin.y/32})]
	end
  end
end

-- dirs : {E, S, W, N}, array of 0/1
local function build_chunk(origin, dirs)
  local surface = game.surfaces[1]
  local cnt = 0
  local sum = {x = 0, y = 0}
  local delta = {x = 1, y = 0}
  for dir, b in ipairs(dirs) do
    cnt = cnt + b
    sum = {x = sum.x + delta.x * b, y = sum.y + delta.y * b}
    delta = {x = -delta.y, y = delta.x}
    if b == 1 and paddings[dir*2] ~= nil then
      -- build paddings
      for _, v in pairs(paddings[dir*2]) do
        surface.create_entity{name=v.name, position={origin.x + v.position.x, origin.y + v.position.y}, force="neutral", direction=v.direction}
      end
    end
  end

  if cnt == 4 then
    build_intersection("allway", origin, {x = 1, y = 0})
  elseif cnt == 3 then
    build_intersection("tshape", origin, {x = sum.y, y = -sum.x})
  elseif cnt == 2 then
    if sum.x == 0 and sum.y == 0 then
      build_intersection("straight", origin, {x = dirs[1], y = dirs[2]})
    else
      build_intersection("corner", origin, {x = (sum.y - sum.x) / 2, y = -(sum.y + sum.x) / 2})
    end
  elseif cnt == 1 then
    build_intersection("ushape", origin, {x = -sum.x, y = -sum.y})
  end
end

local function is_on_grid(gx, gy)
  local bitmap = global.bitmap
  if bitmap[gx] and bitmap[gx][gy] == 1 then
    return true
  else
    return false
  end
end

local function find_connections(gx, gy)
  local dd = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}}
  if is_on_grid(gx, gy) then
    local c = {}
    for _, d in ipairs(dd) do
      if is_on_grid(gx + d[1], gy + d[2]) then
        table.insert(c, 1)
      else
        table.insert(c, 0)
      end
    end
    return c
  else
    return {0,0,0,0}
  end
end

local function disable_items()
  force = game.forces["player"]
  force.recipes["logistic-chest-requester"].enabled = false
  force.recipes["underground-belt"].enabled = false
  force.recipes["fast-underground-belt"].enabled = false
  force.recipes["express-underground-belt"].enabled = false
end


function mymodule.on_chunk_generated(event)
  local bd_box = event.area
  local surface = event.surface
  local chunk_size = 32
  -- assert(chunk_size == bd_box.right_bottom.x - bd_box.left_top.x)
  -- assert(chunk_size == bd_box.right_bottom.y - bd_box.left_top.y)
  if surface ~= game.surfaces[1] then return end

  local gx = bd_box.left_top.x / 32
  local gy = bd_box.left_top.y / 32

  if is_on_grid(gx, gy) then
    -- remove trees and resources
    for _, e in pairs(surface.find_entities_filtered{area=bd_box, type="tree"}) do
      e.destroy()
    end
    for _, e in pairs(surface.find_entities_filtered{area=bd_box, type="resource"}) do
      e.destroy()
    end
    for _, e in pairs(surface.find_entities_filtered{area=bd_box, type="simple-entity"}) do
      e.destroy()
    end
    for _, e in pairs(surface.find_entities_filtered{area=bd_box, force="enemy"}) do
      e.destroy()
    end
    build_chunk({x=gx*chunk_size, y=gy*chunk_size}, find_connections(gx, gy))
  end
end



return mymodule