diff --git a/multi_map_core/init.lua b/multi_map_core/init.lua
index caa3510..1ec00be 100644
--- a/multi_map_core/init.lua
+++ b/multi_map_core/init.lua
@@ -1,7 +1,10 @@
 multi_map = {}
 
-multi_map.number_of_layers = 24
-multi_map.layer_height_chunks = 32
+multi_map.number_of_layers = 24		-- How may layers to generate
+multi_map.layers_start_chunk = 0	-- Y level where to start generatint layers, in chunks
+multi_map.layer_height_chunks = 32	-- Height of each layer, in chunks
+
+-- Either engine defaults or derived from above values
 multi_map.layer_height = multi_map.layer_height_chunks * 80
 multi_map.map_height = 61840
 multi_map.map_min = -30912
@@ -9,15 +12,21 @@ multi_map.map_max = 30927
 multi_map.half_layer_height = multi_map.layer_height / 2
 multi_map.current_layer = nil
 
+-- Can be overridden with someone's own values
 multi_map.bedrock = "multi_map_core:bedrock"
 multi_map.skyrock = "multi_map_core:skyrock"
 
+-- Whether to generate a bedrock layer under a layer/ skyrock above a layer
 multi_map.generate_bedrock = true
 multi_map.generate_skyrock = true
 
+-- Chain of generators
 multi_map.generators = {}
+-- When no suitable generator is found, this generator is used as a fallback
 multi_map.fallback_generator = nil
 
+-- Set the current layer which the mapgen is generating
+-- y = absolute y value to be translated to layer
 function multi_map.set_current_layer(y)
 	for l = 0, multi_map.number_of_layers do
 		if y >= multi_map.map_min + (l * multi_map.layer_height)
@@ -28,11 +37,31 @@ function multi_map.set_current_layer(y)
 	end
 end
 
+-- Get the offset y position, i.e. the y relative to the current layer's center point
+-- y = absolute y value to be translated to y relative to layer center point
 function multi_map.get_offset_y(y)
 	local center_point = multi_map.map_min + (multi_map.current_layer * multi_map.layer_height) + multi_map.half_layer_height
+
+	if center_point > 0 and y > 0 then
+		return math.abs(y) - math.abs(center_point)
+	elseif center_point < 0 and y < 0 then
+		return math.abs(center_point) - math.abs(y)
+	else
+		return center_point - y
+	end
+end
+
+-- Get the absolute y position from a relative offset position
+-- layer = the layer we are in
+-- y = relative y value to be translated to absolute world y position
+function multi_map.get_absolute_y(layer, y)
+	local center_point = multi_map.map_min + (multi_map.current_layer * multi_map.layer_height) + multi_map.half_layer_height
 	return y - center_point
 end
 
+-- Register a fallback generator, which is called in case not suitable generators are found for a layer
+-- generator = the function to call
+-- arguments = optional value or table with values that will be passed to the generator when called
 function multi_map.register_fallback_generator(...)
 	local arg = {...}
 	local generator
@@ -47,6 +76,10 @@ function multi_map.register_fallback_generator(...)
 	multi_map.fallback_generator = { generator = generator, arguments = arguments }
 end
 
+-- Register a generator for all if position is left out or one layer if position is specified
+-- position = the optional layer for which call this generator
+-- generator = the function to call
+-- arguments = optional value or table with values that will be passed to the generator when called
 function multi_map.register_generator(...)
 	local arg = {...}
 	local position
@@ -89,6 +122,7 @@ function multi_map.register_generator(...)
 	end
 end
 
+-- Helper to fill a chunk with a single type of node
 function multi_map.generate_singlenode_chunk(minp, maxp, area, vm_data, content_id)
 	for z = minp.z, maxp.z do
 		for y = minp.y, maxp.y do
@@ -103,6 +137,7 @@ end
 
 local firstrun = true
 -- Global helpers for mapgens
+multi_map.c_ignore = nil
 multi_map.c_stone = nil
 multi_map.c_sandstone = nil
 multi_map.c_air = nil
@@ -115,10 +150,12 @@ minetest.register_on_mapgen_init(function(mapgen_params)
 	if multi_map.number_of_layers * multi_map.layer_height > multi_map.map_height then
 		minetest.log("error", "Number of layers for the given layer height exceeds map height!")
 	end
+	minetest.set_mapgen_params({mgname="singlenode", flags="nolight"})
 end)
 
 minetest.register_on_generated(function(minp, maxp)
 	if firstrun then
+		multi_map.c_ignore = minetest.get_content_id("ignore")
 		multi_map.c_stone = minetest.get_content_id("default:stone")
 		multi_map.c_sandstone = minetest.get_content_id("default:sandstone")
 		multi_map.c_air = minetest.get_content_id("air")
@@ -166,6 +203,7 @@ minetest.register_on_generated(function(minp, maxp)
 		vm:write_to_map(false)
 	else
 		local t = multi_map.generators[multi_map.current_layer]
+
 		if not t then
 			if multi_map.fallback_generator then
 				multi_map.fallback_generator.generator(multi_map.current_layer, minp, maxp, offset_minp, offset_maxp, multi_map.fallback_generator.arguments)
@@ -203,3 +241,159 @@ minetest.register_node("multi_map_core:bedrock", {
 	diggable = false,
 	climbable = false,
 })
+
+
+
+
+--[[
+
+
+function multi_map.calc_lighting(emin, emax, pmin, pmax, propagate_shadow, ground_level)
+	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
+	multi_map.propagate_sunlight(vm, emin, emax, propagate_shadow, ground_level)
+	spread_light(pmin, pmax)
+}
+
+
+function multi_map.propagate_sunlight(vm, emin, emax, propagate_shadow, ground_level)
+	local area = VoxelArea:new({MinEdge = emin, MaxEdge = emax})
+	local vm_data = vm:get_data()
+	local light_data = vm:get_light_data()
+
+	-- const v3s16 &em = vm->m_area.getExtent();
+
+	for z = minp.z, maxp.z do
+		for x = minp.x, maxp.x do
+			local vi = area:index(x, emax.y + 1, z)
+			if vm_data[vi] == multi_map.c_ignore then
+				if block_is_underground then
+					goto continue
+				end
+			elseif (light_data[vi] & 15) ~= 15 and propagate_shadow then
+				goto continue
+			end
+			vi = vi + 1
+			::continue::
+		end
+	end
+
+
+	VoxelArea a(nmin, nmax);
+	bool block_is_underground = (water_level >= nmax.Y);
+	const v3s16 &em = vm->m_area.getExtent();
+
+	// NOTE: Direct access to the low 4 bits of param1 is okay here because,
+	// by definition, sunlight will never be in the night lightbank.
+
+	for (int z = a.MinEdge.Z; z <= a.MaxEdge.Z; z++) {
+		for (int x = a.MinEdge.X; x <= a.MaxEdge.X; x++) {
+			// see if we can get a light value from the overtop
+			u32 i = vm->m_area.index(x, a.MaxEdge.Y + 1, z);
+			if (vm->m_data[i].getContent() == CONTENT_IGNORE) {
+				if (block_is_underground)
+					continue;
+			} else if ((vm->m_data[i].param1 & 0x0F) != LIGHT_SUN &&
+					propagate_shadow) {
+				continue;
+			}
+			VoxelArea::add_y(em, i, -1);
+
+			for (int y = a.MaxEdge.Y; y >= a.MinEdge.Y; y--) {
+				MapNode &n = vm->m_data[i];
+				if (!ndef->get(n).sunlight_propagates)
+					break;
+				n.param1 = LIGHT_SUN;
+				VoxelArea::add_y(em, i, -1);
+			}
+		}
+	}
+	//printf("propagateSunlight: %dms\n", t.stop());
+}
+
+void Mapgen::spreadLight(v3s16 nmin, v3s16 nmax)
+{
+	//TimeTaker t("spreadLight");
+	VoxelArea a(nmin, nmax);
+
+	for (int z = a.MinEdge.Z; z <= a.MaxEdge.Z; z++) {
+		for (int y = a.MinEdge.Y; y <= a.MaxEdge.Y; y++) {
+			u32 i = vm->m_area.index(a.MinEdge.X, y, z);
+			for (int x = a.MinEdge.X; x <= a.MaxEdge.X; x++, i++) {
+				MapNode &n = vm->m_data[i];
+				if (n.getContent() == CONTENT_IGNORE)
+					continue;
+
+				const ContentFeatures &cf = ndef->get(n);
+				if (!cf.light_propagates)
+					continue;
+
+				// TODO(hmmmmm): Abstract away direct param1 accesses with a
+				// wrapper, but something lighter than MapNode::get/setLight
+
+				u8 light_produced = cf.light_source;
+				if (light_produced)
+					n.param1 = light_produced | (light_produced << 4);
+
+				u8 light = n.param1;
+				if (light) {
+					lightSpread(a, v3s16(x,     y,     z + 1), light);
+					lightSpread(a, v3s16(x,     y + 1, z    ), light);
+					lightSpread(a, v3s16(x + 1, y,     z    ), light);
+					lightSpread(a, v3s16(x,     y,     z - 1), light);
+					lightSpread(a, v3s16(x,     y - 1, z    ), light);
+					lightSpread(a, v3s16(x - 1, y,     z    ), light);
+				}
+			}
+		}
+	}
+
+	//printf("spreadLight: %dms\n", t.stop());
+}
+
+
+
+function multi_map.light_spread(area, v3s16 p, u8 light)
+{
+	if (light <= 1 || !a.contains(p))
+		return;
+
+	u32 vi = vm->m_area.index(p);
+	MapNode &n = vm->m_data[vi];
+
+	// Decay light in each of the banks separately
+	u8 light_day = light & 0x0F;
+	if (light_day > 0)
+		light_day -= 0x01;
+
+	u8 light_night = light & 0xF0;
+	if (light_night > 0)
+		light_night -= 0x10;
+
+	// Bail out only if we have no more light from either bank to propogate, or
+	// we hit a solid block that light cannot pass through.
+	if ((light_day  <= (n.param1 & 0x0F) &&
+		light_night <= (n.param1 & 0xF0)) ||
+		!ndef->get(n).light_propagates)
+		return;
+
+	// Since this recursive function only terminates when there is no light from
+	// either bank left, we need to take the max of both banks into account for
+	// the case where spreading has stopped for one light bank but not the other.
+	light = MYMAX(light_day, n.param1 & 0x0F) |
+			MYMAX(light_night, n.param1 & 0xF0);
+
+	n.param1 = light;
+
+	lightSpread(a, p + v3s16(0, 0, 1), light);
+	lightSpread(a, p + v3s16(0, 1, 0), light);
+	lightSpread(a, p + v3s16(1, 0, 0), light);
+	lightSpread(a, p - v3s16(0, 0, 1), light);
+	lightSpread(a, p - v3s16(0, 1, 0), light);
+	lightSpread(a, p - v3s16(1, 0, 0), light);
+}
+
+
+
+
+
+]]--
\ No newline at end of file
diff --git a/multi_map_generators/mmgen_levels.lua b/multi_map_generators/mmgen_levels.lua
index 11359bb..d07017c 100644
--- a/multi_map_generators/mmgen_levels.lua
+++ b/multi_map_generators/mmgen_levels.lua
@@ -112,6 +112,7 @@ function mmgen_levels.generate(current_layer, minp, maxp, offset_minp, offset_ma
 	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
 	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
 	local data = vm:get_data()
+	local light_data = vm:get_light_data()
 	
 	local c_stone = minetest.get_content_id("default:stone")
 	local c_sand  = minetest.get_content_id("default:sand")
@@ -232,6 +233,14 @@ function mmgen_levels.generate(current_layer, minp, maxp, offset_minp, offset_ma
 					end
 				end
 
+--				if relative_y < 0 then
+--					if relative_y > -15 then
+--						light_data[vi] = 15 + relative_y
+--					else
+--						light_data[vi] = 0
+--					end
+--				end
+
 				ni3d = ni3d + 1
 				ni2d = ni2d + 1
 				vi = vi + 1
@@ -243,13 +252,12 @@ function mmgen_levels.generate(current_layer, minp, maxp, offset_minp, offset_ma
 	end
 
 	vm:set_data(data)
-	if oy0 < 0 then
-		vm:set_lighting({day=0, night=0})
-	else
-		vm:set_lighting({day=15, night=0})
-	end
+--	vm:set_light_data(light_data)
+--	if oy0 < 0 then
+--		vm:set_lighting({day=0, night=0})
+--	end
 	vm:calc_lighting()
-	vm:write_to_map(data)
+	vm:write_to_map()
 	vm:update_liquids()
 
 end