Random penalty noise expression with seed gives non-random results

[Natha]

I implemented this noise expression:

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{
	type = "noise-expression",
	name = "random-value-0-1",
	expression = noise.to_noise_expression(noise.to_noise_expression{
	  type = "function-application",
	  function_name = "random-penalty",
	  arguments = {
		x = noise.var("x"),
		y = noise.var("y"),
		source = noise.to_noise_expression(100),
		amplitude = noise.to_noise_expression(100),
		seed = noise.var("map_seed")
	  }
	} / 100) -- cannot use noise.random_between() here because we need to consider map seed
  },

which gives this result:

Unbenannt.PNG (127.45 KiB) Viewed 754 times

As you can see, values are not random for the same x-value. When I use a constant number seed, the results are random.

[Genhis]

Thanks for the report. How do you get the visualisation and what are X/Y coordinates of the tiles? Ideally I'm looking for something which I can just copy-paste and get the same result. Based on the C++ code, this is very unlikely to happen, so either you hit an edge case or your debug visualisation is incorrect.

[Natha]

Thanks for the report. How do you get the visualisation and what are X/Y coordinates of the tiles? Ideally I'm looking for something which I can just copy-paste and get the same result. Based on the C++ code, this is very unlikely to happen, so either you hit an edge case or your debug visualisation is incorrect.

I assigned this expression to a property in map_gen_settings:

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property_expression_names = {["probability"] = "random-value-0-1"}

(Another issue that I noticed is that if you name the property the same as the expression, it won't be taken)

Then I had a test mod which does the following upon running a command:

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local pos_arr = get_area_positions(get_area(player.position, 32)) -- just returns an array full of positions, 2 chunks around the player
		local props = {"probability"}
		for _,p in ipairs(pos_arr) do
			local calcresult = player.surface.calculate_tile_properties(props, {p})
			if calcresult[props[1]] then
				rendering.draw_text{text=string.format("%.4f", calcresult[props[1]][1]), color={1, 1, 1}, surface=player.surface, target=p, scale=0.5, time_to_live=600}
			end
		end

What I just figured out: the issue only occurs when I pass only one position to calculate_tile_properties. If I pass the whole array, the result is completely random (but then different result if the array changes).

Passing the map seed as literal number for random penalty seed gives the same columned result. But passing 1 as literal number gives a random result. Could this be a data type length issue?

Anyway, in my opinion the random penalty should not rely on the position array.
I'm going to setup a test mod for you to reproduce.

[Natha]

This mod shows what I mean:
/test [a, b] [p1, p2, p3]

a is calculate_tile_properties once for each position
b is calculate_tile_properties with whole position array

p1 is a random value noise expression with seed 100
p2 is with map seed variable
p3 is with a literal number which represents a map seed

[Genhis]

Passing the map seed as literal number for random penalty seed gives the same columned result. But passing 1 as literal number gives a random result. Could this be a data type length issue?

It's possible. Random penalty expects batch inputs (not single values) because it has a random generator with side effects - the first position determines the seed for the whole batch. It usually runs on a chunk.

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RandomGenerator rand((int32_t(x[0]) + 213) * 7919 + (int32_t(y[0] + seed) + 315) * 7907);
for (size_t i = cache.vectorSize; i-- > 0;)
  dest[i] = source[i] <= 0 ? source[i] : source[i] - rand.uniformDouble() * amplitude;

If you want to replicate base game map generation, this topic may be useful to you: viewtopic.php?f=25&t=113146
To learn more about our random generator, see this: viewtopic.php?f=34&t=70588