write something there

mods/minetest_game/weather/README.txt

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+Minetest Game mod: weather
+==========================
+See license.txt for license information.
+Source code by paramat (MIT).

mods/minetest_game/weather/api.lua

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+local CYCLE = 8 -- Time period of cyclic clouds update in seconds
+
+weather = {}
+
+-- default implementation is empty
+function weather.get(player)
+	return {}
+end
+
+local function do_update()
+	for _, player in ipairs(minetest.get_connected_players()) do
+		local params = weather.get(player)
+		assert(params ~= nil, "weather.get() must not return nil")
+		if params.clouds then
+			player:set_clouds(params.clouds)
+		end
+		if params.lighting then
+			player:set_lighting(params.lighting)
+		end
+	end
+end
+
+local function cyclic_update()
+	do_update()
+	minetest.after(CYCLE, cyclic_update)
+end
+minetest.after(0, cyclic_update)
+
+-- Update on player join to instantly alter clouds from the default
+minetest.register_on_joinplayer(function(player)
+	do_update()
+end)

mods/minetest_game/weather/init.lua

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+-- Always load the API
+dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/api.lua")
+
+-- Disable by mapgen or setting
+
+if minetest.settings:get_bool("enable_weather") == false then
+	return
+end
+
+local mg_name = minetest.get_mapgen_setting("mg_name")
+if mg_name == "v6" or mg_name == "singlenode" then
+	-- set a default shadow intensity for mgv6 and singlenode
+	minetest.register_on_joinplayer(function(player)
+		player:set_lighting({
+			shadows = { intensity = 0.33 },
+			bloom = { intensity = 0.05 },
+			volumetric_light = { strength = 0.2 },
+		})
+	end)
+
+	return
+end
+
+-- Default implementation for noise based cloud appearance
+
+local TSCALE = 600 -- Time scale of noise variation in seconds
+
+local np_density = {
+	offset = 0.5,
+	scale = 0.5,
+	spread = {x = TSCALE, y = TSCALE, z = TSCALE},
+	seed = 813,
+	octaves = 1,
+	persist = 0,
+	lacunarity = 2,
+}
+
+local np_thickness = {
+	offset = 0.5,
+	scale = 0.5,
+	spread = {x = TSCALE, y = TSCALE, z = TSCALE},
+	seed = 96,
+	octaves = 1,
+	persist = 0,
+	lacunarity = 2,
+}
+
+local np_speedx = {
+	offset = 0,
+	scale = 1,
+	spread = {x = TSCALE, y = TSCALE, z = TSCALE},
+	seed = 911923,
+	octaves = 1,
+	persist = 0,
+	lacunarity = 2,
+}
+
+local np_speedz = {
+	offset = 0,
+	scale = 1,
+	spread = {x = TSCALE, y = TSCALE, z = TSCALE},
+	seed = 5728,
+	octaves = 1,
+	persist = 0,
+	lacunarity = 2,
+}
+
+local nobj_density = nil
+local nobj_thickness = nil
+local nobj_speedx = nil
+local nobj_speedz = nil
+
+local function rangelim(value, lower, upper)
+	return math.min(math.max(value, lower), upper)
+end
+
+local t_offset
+do
+	local meta = minetest.get_mod_storage()
+	if meta:contains("time_offset") then
+		t_offset = meta:get_int("time_offset")
+	else
+		-- Use random offset so not each new world behaves the same.
+		t_offset = math.random(0, 300000)
+		meta:set_int("time_offset", t_offset)
+	end
+end
+
+function weather.get(player)
+	-- Adjusted time in seconds
+	local time = math.floor(minetest.get_gametime() - t_offset)
+
+	nobj_density = nobj_density or minetest.get_perlin(np_density)
+	nobj_thickness = nobj_thickness or minetest.get_perlin(np_thickness)
+	nobj_speedx = nobj_speedx or minetest.get_perlin(np_speedx)
+	nobj_speedz = nobj_speedz or minetest.get_perlin(np_speedz)
+
+	local n_density = nobj_density:get_2d({x = time, y = 0}) -- 0 to 1
+	local n_thickness = nobj_thickness:get_2d({x = time, y = 0}) -- 0 to 1
+	local n_speedx = nobj_speedx:get_2d({x = time, y = 0}) -- -1 to 1
+	local n_speedz = nobj_speedz:get_2d({x = time, y = 0}) -- -1 to 1
+
+	-- Fallback to mid-value 50 for very old worlds
+	local humid = minetest.get_humidity(player:get_pos()) or 50
+	-- Default and classic density value is 0.4, make this happen
+	-- at humidity midvalue 50 when n_density is at midvalue 0.5.
+	-- density_max = 0.25 at humid = 0.
+	-- density_max = 0.8 at humid = 50.
+	-- density_max = 1.35 at humid = 100.
+	local density_max = 0.8 + ((humid - 50) / 50) * 0.55
+	-- Range limit density_max to always have occasional
+	-- small scattered clouds at extreme low humidity.
+	local density = rangelim(density_max, 0.2, 1.0) * n_density
+
+	return {
+		clouds = {
+			density = density,
+			thickness = math.max(math.floor(
+				rangelim(32 * humid / 100, 8, 32) * n_thickness
+				), 2),
+			speed = {x = n_speedx * 4, z = n_speedz * 4},
+		},
+		lighting = {
+			shadows = { intensity = 0.7 * (1 - density) },
+			bloom = { intensity = 0.05 },
+			volumetric_light = { strength = 0.2 },
+		}
+	}
+end

mods/minetest_game/weather/license.txt

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+License of source code
+----------------------
+
+The MIT License (MIT)
+Copyright (C) 2019 paramat
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this
+software and associated documentation files (the "Software"), to deal in the Software
+without restriction, including without limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of the Software, and to permit
+persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or
+substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+
+For more details:
+https://opensource.org/licenses/MIT

mods/minetest_game/weather/mod.conf

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+name = weather
+description = Minetest Game mod: weather