fix ground_y searching bug

fixes #18

M  readme.txt
M  src/mapgen_v6.lua

readme.txt

@@ -1,19 +1,19 @@
-   _____                       __  __           _ 
+   _____                       __  __           _
   / ____|                     |  \/  |         | |
  | (___  _ __   _____      __ | \  / | ___   __| |
   \___ \| '_ \ / _ \ \ /\ / / | |\/| |/ _ \ / _` |
   ____) | | | | (_) \ V  V /  | |  | | (_) | (_| |
  |_____/|_| |_|\___/ \_/\_/   |_|  |_|\___/ \__,_|
-				
+
 					Version 3.2
-				
+
 By Splizard and LazyJ.
 
 Minetest version:  0.4.9
 Depends: default
 License:  GPL v2
 
-Complimentary Mods: 
+Complimentary Mods:
 ---------------------
 *	"Snowdrift" by paramat
 *	"More Blocks" by Calinou (2014_05_11 or newer)
@@ -62,7 +62,7 @@ There are nine biome types:
 * Alpine
 * Snowy
 * Plain
-  
+
 Snow can be picked up and thrown as snowballs or stacked into snow blocks.
 Snow and ice melts when near warm blocks such as torches or igniters such as lava.
 Snow blocks freeze water source blocks around them.
@@ -101,3 +101,9 @@ As admin you can use the /snow command in-game to make various changes.
 UNINSTALL:
 ------------
 Simply delete the folder snow from the mods folder.
+
+
+
+TODO:
+— use the settingtypes.txt
+— test if the fixed ground_y search works correctly at chunkcorners at ground level

src/mapgen_v6.lua

@@ -41,9 +41,9 @@ local function do_ws_func(a, x)
 	local n = math.pi * x / 16000
 	local y = 0
 	for k = 1,1000 do
-		y = y + 1000*math.sin(k^a * n)/(k^a)
+		y = y + math.sin(k^a * n)/(k^a)
 	end
-	return y/math.pi
+	return 1000*y/math.pi
 end
 
 
@@ -184,19 +184,19 @@ minetest.register_on_generated(function(minp, maxp, seed)
 		define_contents()
 	end
 
-	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
-	local area = VoxelArea:new({MinEdge=emin, MaxEdge=emax})
+	local vm, emin, emax = minetest.get_mapgen_object"voxelmanip"
+	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
 	local data = vm:get_data()
 	local param2s = vm:get_param2_data()
 
-	local heightmap = minetest.get_mapgen_object("heightmap")
+	local heightmap = minetest.get_mapgen_object"heightmap"
 
 	local snow_tab,num = {},1
 	local pines_tab,pnum = {},1
 
 	local sidelen = x1 - x0 + 1
 	local chulens = {x=sidelen, y=sidelen, z=sidelen}
-	local nvals_default = minetest.get_perlin_map(np_default, chulens):get2dMap_flat({x=x0+150, y=z0+50})
+	local nvals_default = minetest.get_perlin_map(np_default, chulens):get2dMap_flat{x=x0+150, y=z0+50}
 	local nvals_cold, nvals_ice
 
 	-- Choose biomes
@@ -224,7 +224,7 @@ minetest.register_on_generated(function(minp, maxp, seed)
 		local test
 		if nvals_default[ni] < 0.35 then
 			if not nvals_cold then
-				nvals_cold = minetest.get_perlin_map(np_cold, chulens):get2dMap_flat({x=x0, y=z0})
+				nvals_cold = minetest.get_perlin_map(np_cold, chulens):get2dMap_flat{x=x0, y=z0}
 			end
 			test = math.min(nvals_cold[ni], 1)
 			if smooth then
@@ -246,10 +246,12 @@ minetest.register_on_generated(function(minp, maxp, seed)
 			and test > smooth_rarity_min then
 				-- remove trees near alpine
 				local ground_y
-				for y = math.min(heightmap[ni]+20, maxp.y), math.max(minp.y, heightmap[ni]-5), -1 do
-					if data[area:index(x, y, z)] ~= c.air then
-						ground_y = y
-						break
+				if data[area:index(x, maxp.y, z)] == c.air then
+					for y = math.min(heightmap[ni]+20, maxp.y), math.max(minp.y, heightmap[ni]-5), -1 do
+						if data[area:index(x, y, z)] ~= c.air then
+							ground_y = y
+							break
+						end
 					end
 				end
 
@@ -279,7 +281,7 @@ minetest.register_on_generated(function(minp, maxp, seed)
 			nodes_added = true
 			write_to_map = true
 			if not nvals_ice then
-				nvals_ice = minetest.get_perlin_map(np_ice, chulens):get2dMap_flat({x=x0, y=z0})
+				nvals_ice = minetest.get_perlin_map(np_ice, chulens):get2dMap_flat{x=x0, y=z0}
 			end
 			local icetype = nvals_ice[ni]
 			local cool = icetype > 0 -- only spawns ice on edge of water
@@ -290,11 +292,14 @@ minetest.register_on_generated(function(minp, maxp, seed)
 
 
 			local ground_y
-			for y = math.min(heightmap[ni]+20, maxp.y), math.max(minp.y, heightmap[ni]-5), -1 do
-				local nodid = data[area:index(x, y, z)]
-				if nodid ~= c.air then
-					ground_y = y
-					break
+			-- avoid generating underground
+			if data[area:index(x, maxp.y, z)] == c.air then
+				-- search for non air node from 20 m above ground down to 5 m below ground (confined by minp and maxp)
+				for y = math.min(heightmap[ni]+20, maxp.y), math.max(minp.y, heightmap[ni]-5), -1 do
+					if data[area:index(x, y, z)] ~= c.air then
+						ground_y = y
+						break
+					end
 				end
 			end