Re-organized the code. All polygon-related calculations go to polygons.lua.

polygons.lua

@@ -0,0 +1,166 @@
+local modpath = minetest.get_modpath(minetest.get_current_modname()) .. '/'
+local worldpath = minetest.get_worldpath() .. '/'
+local load_map = dofile(modpath .. 'load.lua')
+
+local function copy_if_needed(filename)
+	local wfilename = worldpath..filename
+	local wfile = io.open(wfilename, 'r')
+	if wfile then
+		wfile:close()
+		return
+	end
+	local mfilename = modpath..filename
+	local mfile = io.open(mfilename, 'r')
+	local wfile = io.open(wfilename, 'w')
+	wfile:write(mfile:read("*all"))
+	mfile:close()
+	wfile:close()
+end
+
+copy_if_needed('size')
+local sfile = io.open(worldpath..'size')
+local X = tonumber(sfile:read('*l'))
+local Z = tonumber(sfile:read('*l'))
+sfile:close()
+
+copy_if_needed('dem')
+local dem = load_map('dem', 2, true, X*Z)
+copy_if_needed('lakes')
+local lakes = load_map('lakes', 2, true, X*Z)
+copy_if_needed('bounds_x')
+local bounds_x = load_map('bounds_x', 4, false, (X-1)*Z)
+copy_if_needed('bounds_y')
+local bounds_z = load_map('bounds_y', 4, false, X*(Z-1))
+
+copy_if_needed('offset_x')
+local offset_x = load_map('offset_x', 1, true, X*Z)
+for k, v in ipairs(offset_x) do
+	offset_x[k] = (v+0.5)/256
+end
+
+copy_if_needed('offset_y')
+local offset_z = load_map('offset_y', 1, true, X*Z)
+for k, v in ipairs(offset_z) do
+	offset_z[k] = (v+0.5)/256
+end
+
+local function index(x, z)
+	return z*X+x+1
+end
+
+local blocksize = mapgen_rivers.blocksize
+local min_catchment = mapgen_rivers.min_catchment
+local max_catchment = mapgen_rivers.max_catchment
+
+-- Width coefficients: coefficients solving
+--   wfactor * min_catchment ^ wpower = 1/(2*blocksize)
+--   wfactor * max_catchment ^ wpower = 1
+local wpower = math.log(2*blocksize)/math.log(max_catchment/min_catchment)
+local wfactor = 1 / max_catchment ^ wpower
+local function river_width(flow)
+	flow = math.abs(flow)
+	if flow < min_catchment then
+		return 0
+	end
+
+	return math.min(wfactor * flow ^ wpower, 1)
+end
+
+local function make_polygons(minp, maxp)
+	local chulens = maxp.z - minp.z + 1
+
+	local polygons = {}
+	local xpmin, xpmax = math.max(math.floor(minp.x/blocksize - 0.5), 0), math.min(math.ceil(maxp.x/blocksize), X-2)
+	local zpmin, zpmax = math.max(math.floor(minp.z/blocksize - 0.5), 0), math.min(math.ceil(maxp.z/blocksize), Z-2)
+
+	for xp = xpmin, xpmax do
+		for zp=zpmin, zpmax do
+			local iA = index(xp, zp)
+			local iB = index(xp+1, zp)
+			local iC = index(xp+1, zp+1)
+			local iD = index(xp, zp+1)
+			local poly_x = {offset_x[iA]+xp, offset_x[iB]+xp+1, offset_x[iC]+xp+1, offset_x[iD]+xp}
+			local poly_z = {offset_z[iA]+zp, offset_z[iB]+zp, offset_z[iC]+zp+1, offset_z[iD]+zp+1}
+			local polygon = {x=poly_x, z=poly_z, i={iA, iB, iC, iD}}
+
+			local bounds = {}
+			local xmin = math.max(math.floor(blocksize*math.min(unpack(poly_x)))+1, minp.x)
+			local xmax = math.min(math.floor(blocksize*math.max(unpack(poly_x))), maxp.x)
+			for x=xmin, xmax do
+				bounds[x] = {}
+			end
+
+			local i1 = 4
+			for i2=1, 4 do -- Loop on 4 edges
+				local x1, x2 = poly_x[i1], poly_x[i2]
+				local lxmin = math.floor(blocksize*math.min(x1, x2))+1
+				local lxmax = math.floor(blocksize*math.max(x1, x2))
+				if lxmin <= lxmax then
+					local z1, z2 = poly_z[i1], poly_z[i2]
+					local a = (z1-z2) / (x1-x2)
+					local b = blocksize*(z1 - a*x1)
+					for x=math.max(lxmin, minp.x), math.min(lxmax, maxp.x) do
+						table.insert(bounds[x], a*x+b)
+					end
+				end
+				i1 = i2
+			end
+			for x=xmin, xmax do
+				local xlist = bounds[x]
+				table.sort(xlist)
+				local c = math.floor(#xlist/2)
+				for l=1, c do
+					local zmin = math.max(math.floor(xlist[l*2-1])+1, minp.z)
+					local zmax = math.min(math.floor(xlist[l*2]), maxp.z)
+					local i = (x-minp.x) * chulens + (zmin-minp.z) + 1
+					for z=zmin, zmax do
+						polygons[i] = polygon
+						i = i + 1
+					end
+				end
+			end
+
+			polygon.dem = {dem[iA], dem[iB], dem[iC], dem[iD]}
+			polygon.lake = math.min(lakes[iA], lakes[iB], lakes[iC], lakes[iD])
+
+			local river_west = river_width(bounds_z[iA])
+			local river_north = river_width(bounds_x[iA-zp])
+			local river_east = 1-river_width(bounds_z[iB])
+			local river_south = 1-river_width(bounds_x[iD-zp-1])
+			if river_west > river_east then
+				local mean = (river_west + river_east) / 2
+				river_west = mean
+				river_east = mean
+			end
+			if river_north > river_south then
+				local mean = (river_north + river_south) / 2
+				river_north = mean
+				river_south = mean
+			end
+			polygon.rivers = {river_west, river_north, river_east, river_south}
+
+			local around = {0,0,0,0,0,0,0,0}
+			if zp > 0 then
+				around[1] = river_width(bounds_z[iA-X])
+				around[2] = river_width(bounds_z[iB-X])
+			end
+			if xp < X-2 then
+				around[3] = river_width(bounds_x[iB-zp])
+				around[4] = river_width(bounds_x[iC-zp-1])
+			end
+			if zp < Z-2 then
+				around[5] = river_width(bounds_z[iC])
+				around[6] = river_width(bounds_z[iD])
+			end
+			if xp > 0 then
+				around[7] = river_width(bounds_x[iD-zp-2])
+				around[8] = river_width(bounds_x[iA-zp-1])
+			end
+			polygon.river_corners = {math.max(around[8], around[1]), math.max(around[2], around[3]), math.max(around[4], around[5]), math.max(around[6], around[7])}
+		end
+	end
+
+	return polygons
+end
+
+return make_polygons