Find minetest sunlight

light_detection.lua

-- See daynightratio.h:23
local dnrvalues = {
	{4250 + 125, 150},
	{4500 + 125, 150},
	{4750 + 125, 250},
	{5000 + 125, 350},
	{5250 + 125, 500},
	{5500 + 125, 675},
	{5750 + 125, 875},
	{6000 + 125, 1000},
	{6250 + 125, 1000},
}
local function time_to_daynight_ratio(tod)
	tod = tod * 24000
	assert(tod >= 0 and tod <= 24000, "invalid time of day")
	if tod > 12000 then
		tod = 24000 - tod
	end
	for i = 1,#dnrvalues do
		if dnrvalues[i][1] > tod then
			if i == 1 then
				return dnrvalues[1][2]
			end
			local td0 = dnrvalues[i][1] - dnrvalues[i - 1][1]
			local f = (tod - dnrvalues[i - 1][1]) / td0
			return f * dnrvalues[i][2] + (1.0 - f) * dnrvalues[i - 1][2]
		end
	end
	return 1000
end

-- the offsets for neighbouring nodes with given order
local dirs = {
	{x=-1, y=0, z=0}, {x=1, y=0, z=0}, {x=0, y=0, z=-1}, {x=0, y=0, z=1},
	{x=0, y=-1, z=0}, {x=0, y=1, z=0}
}

-- walks nodes to find the daylight when it's not known
local function find_sunlight(pos)
	local found_light = 0
	local todo = {{pos, 0}}
	local sp = 1
	local dists = {}
	dists[core.hash_node_position(pos)] = 0
	while sp > 0 do
		local pos, dist = unpack(todo[sp])
		sp = sp - 1
		dist = dist + 1
		for i = 1, 6 do
			local p = vector.add(pos, dirs[i])
			local h = core.hash_node_position(p)
			if not dists[h]
			or dist < dists[h] then
				-- position to walk
				local node = core.get_node(p)
				local def = core.registered_nodes[node.name]
				if def and def.sunlight_propagates then
					-- can walk here
					local daylight = node.param1 % 16
					local possible_finlight = daylight - dist
					if possible_finlight > found_light then
						-- from here brighter sunlight could come from
						local nightlight = math.floor(node.param1 / 16)
						if daylight > nightlight then
							-- found a valid daylight
							found_light = possible_finlight
						else
							-- sunlight may be darker, so walk it's neighbours
							sp = sp + 1
							todo[sp] = {p, dist}
						end
					end
					dists[h] = dist
				else
					-- avoid testing propagation at the same position again
					dists[h] = -1
				end
			end
		end
	end
	return found_light
end

-- See light.h:119
function core.get_natural_light(pos, tod)
	local param1 = core.get_node(pos).param1
	local daylight = param1 % 16
	if daylight == 0 then
		return 0
	end
	if daylight == math.floor(param1 / 16) then
		daylight = find_sunlight(pos)
	end
	tod = tod or core.get_timeofday()
	local sun_factor = time_to_daynight_ratio(tod)
	return math.min(math.floor(sun_factor * daylight / 1000), 15)
end

function core.get_artificial_light(param1)
	return math.floor(param1 / 16)
end