minetest-mod-snow/src/falling_snow.lua

-- Parameters

local function snow_fall(pos)
	local ground_y = nil
	for y=pos.y+10,pos.y+20,1 do
		local n = minetest.get_node({x=pos.x,y=y,z=pos.z}).name
		if n ~= "air" and n ~= "ignore" then
			return
		end
	end
	for y=pos.y+9,pos.y-15,-1 do
		local n = minetest.get_node({x=pos.x,y=y,z=pos.z}).name
		if n ~= "air" and n ~= "ignore" then
			ground_y = y
			break
		end
	end
	if not ground_y then
		return
	end

	pos = {x=pos.x, y=ground_y, z=pos.z}

	snow.place(pos, true)
	--minetest.place_node({x=pos.x, y=pos.y+2, z=pos.z}, {name="default:snow"}) -- LazyJ
end

local YLIMIT = 1 -- Set to world's water level
				-- Particles are timed to disappear at this y
				-- Particles do not spawn when player's head is below this y
local PRECSPR = 6 -- Time scale for precipitation variation in minutes
local PRECOFF = -0.4 -- Precipitation offset, higher = rains more often
local GSCYCLE = 0.5 -- Globalstep cycle (seconds)
local FLAKES = 32 -- Snowflakes per cycle
--~ local DROPS = 128 -- Raindrops per cycle
--~ local RAINGAIN = 0.2 -- Rain sound volume
local COLLIDE = false -- Whether particles collide with nodes
local NISVAL = 39 -- Clouds RGB value at night
local DASVAL = 175 -- Clouds RGB value in daytime

local np_prec = {
	offset = 0,
	scale = 1,
	spread = {x = PRECSPR, y = PRECSPR, z = PRECSPR},
	seed = 813,
	octaves = 1,
	persist = 0,
	lacunarity = 2.0,
	--flags = ""
}

-- These 2 must match biome heat and humidity noise parameters for a world

local np_temp = {
	offset = 50,
	scale = 50,
	spread = {x = 1000, y = 1000, z = 1000},
	seed = 5349,
	octaves = 3,
	persist = 0.5,
	lacunarity = 2.0,
	--flags = ""
}

local np_humid = {
	offset = 50,
	scale = 50,
	spread = {x = 1000, y = 1000, z = 1000},
	seed = 842,
	octaves = 3,
	persist = 0.5,
	lacunarity = 2.0,
	--flags = ""
}


-- Stuff

local difsval = DASVAL - NISVAL
local grad = 14 / 95
local yint = 1496 / 95



-- Globalstep function
local timer = 0

if snow.enable_snowfall then
	minetest.register_globalstep(function(dtime)
		timer = timer + dtime
		if timer < GSCYCLE then
			return
		end

		timer = 0

		for _, player in ipairs(minetest.get_connected_players()) do
			local player_name = player:get_player_name()
			local pos_player = player:getpos()
			local pposy = math.floor(pos_player.y) + 2 -- Precipitation when swimming
			if pposy >= YLIMIT - 2 then
				local pposx = math.floor(pos_player.x)
				local pposz = math.floor(pos_player.z)
				local ppos = {x = pposx, y = pposy, z = pposz}

				local nobj_temp = minetest.get_perlin(np_temp)
				local nobj_humid = minetest.get_perlin(np_humid)
				local nobj_prec = minetest.get_perlin(np_prec)

				local nval_temp = nobj_temp:get2d({x = pposx, y = pposz})
				local nval_humid = nobj_humid:get2d({x = pposx, y = pposz})
				local nval_prec = nobj_prec:get2d({x = os.clock() / 60, y = 0})

				-- Biome system: Frozen biomes below heat 35,
				-- deserts below line 14 * t - 95 * h = -1496
				-- h = (14 * t + 1496) / 95
				-- h = 14/95 * t + 1496/95
				-- where 14/95 is gradient and 1496/95 is y intersection
				-- h - 14/95 t = 1496/95 y intersection
				-- so area above line is
				-- h - 14/95 t > 1496/95
				local freeze = nval_temp < 35
				local precip = nval_prec < (nval_humid - 50) / 50 + PRECOFF and
					nval_humid - grad * nval_temp > yint

				if snow.debug then
					precip = true
				end

				-- Check if player is outside
				local outside = minetest.get_node_light(ppos, 0.5) == 15

				-- Occasionally reset player sky
				if math.random() < 0.1 then
					if precip then
						-- Set overcast sky
						local sval
						local time = minetest.get_timeofday()
						if time >= 0.5 then
							time = 1 - time
						end
						-- Sky brightness transitions:
						-- First transition (24000 -) 4500, (1 -) 0.1875
						-- Last transition (24000 -) 5750, (1 -) 0.2396
						if time <= 0.1875 then
							sval = NISVAL
						elseif time >= 0.2396 then
							sval = DASVAL
						else
							sval = math.floor(NISVAL +
								((time - 0.1875) / 0.0521) * difsval)
						end
						-- Set sky to overcast bluish-grey
						player:set_sky(
							{r = sval, g = sval, b = sval + 16, a = 255},
							"plain",
							{}
						)
					else
						-- Reset sky to normal
						player:set_sky({}, "regular", {})
					end
				end

				if precip and outside then
					-- Precipitation
					if freeze then
						-- Snowfall
						local extime = math.min((pposy + 12 - YLIMIT) / 2, 9)

						local x, y, z = pposx - 24 + math.random(0, 48), pposy + 12, pposz - 24 + math.random(0, 48)

						if not snow.lighter_snowfall then
							snow_fall({
										x = x,
										y = y,
										z = z
									}, true)
						end

						for _ = 1, FLAKES do

							x, y, z = pposx - 24 + math.random(0, 48), pposy + 12, pposz - 24 + math.random(0, 48)

							minetest.add_particle({
								pos = {
									x = x,
									y = y,
									z = z
								},
								velocity = {
									x = (-20 + math.random(0, 40)) / 100,
									y = -2.0,
									z = (-20 + math.random(0, 40)) / 100
								},
								acceleration = {x = 0, y = 0, z = 0},
								expirationtime = extime,
								size = 2.8,
								collisiondetection = COLLIDE,
								collision_removal = true,
								vertical = false,
								texture = "snowdrift_snowflake" ..
									math.random(1, 12) .. ".png",
								playername = player_name
							})
						end
					end
				end
			end
		end
	end)
end