Deterministic random number

[leadraven]

Hello.
I need a random value determined by coordinates. Currently I'm using math.randomseed for each coordinates I need. Is it a correct way? Won't it break anything in other mods? Will it work properly in multiplayer?
Or, may be, I'd better to use local instance of RNG? If so, how to create it?
How can I upgrade it to be based not only on coordinates, but also on the map seed?

[darkfrei]

Do you need nice noise on the map or every position can have any value?

[leadraven]

Do you need nice noise on the map or every position can have any value?

Independent value for each position.

[orzelek]

You can use LuaRandomGenerator for that but you still need to seed it.

You can find example in RSO in method rng_for_reg_pos.
It's still not perfect since you need to do some magic to create seed from coordinates to prevent bands and symetry. And lua is not exactly nice to play with when you want to overflow int's. Some internet research might net a better method of turning x, y pair into a seed.

[leadraven]

It's still not perfect since you need to do some magic to create seed from coordinates to prevent bands and symetry.

math.randomseed(x)
local seedx = math.random(math.mininteger, math.maxinteger)
math.randomseed(y)
local seedy = math.random(math.mininteger, math.maxinteger)
math.randomseed(seedx+seedy)
local rnd = math.random()

It works, but is it the "correct" way?

[DaveMcW]

Calling math.randomseed() more than once in a program is bad! Factorio already calls it once with the map seed, so mods should not call it at all.

Use LuaRandomGenerator instead.

Code: Select all

function position_random(pos)
  --[[ Generator only accepts even-numbered seeds from 172 to 4294967294. ]]
  local seed = (math.floor(pos.x) % 46340 * 46340 + math.floor(pos.y) % 46340 + 86) * 2
  local generator = game.create_random_generator(seed)

  --[[ Throw away the first few numbers because they are not very random. ]] 
  for i = 1, 16 do 
    generator()  
  end
  return generator()
end

--[[ Test ]]
local player = game.players[1]
for x = player.position.x - 20, player.position.x + 20 do
  for y = player.position.y - 20, player.position.y + 20 do
    local pos = {x=x, y=y}
    player.surface.create_entity{
      name = "flying-text",
      text = math.floor(position_random(pos) * 100),
      force = player.force,
      position = pos,
    }
  end
end

[Bilka]

Calling math.randomseed() more than once in a program is bad!

In factorio it doesnt do anything so you can call it as often as you want :P