Added option to add trains to a pre-generated map.

This should save lots of cpu time by removing the higly cpu-intensive
map generating steps.

Benchmark:
Generating map completely: 30.493s
Adding trains:              0.157s

This benchmark was obtained from the data of the Linuxworks server,
which has about 500k nodes and about 600 trains.

main.lua

@@ -93,6 +93,32 @@ dofile("track_defs.lua")
 dofile("nodedb.lua")
 
 
+function parse_args(argv) 
+	local i = 1
+	local no_trains = false
+	local datapath, mappath
+	while i <= #argv do
+		local a = argv[i]
+		if (a == "-m") or (a == "--map-file") then
+			-- only draw trains – requires specifying an already drawn file
+			i = i+1
+			if not argv[i] then
+				error(("missing filename after `%s'"):format(a))
+			end
+			mappath = argv[i]
+		elseif (a == "-t") or (a == "--no-trains") then
+			-- do not draw trains
+			no_trains = true
+		else
+			datapath = a
+		end
+		i = i + 1
+	end
+	return datapath, mappath, no_trains
+end
+
+datapath, mappath, no_trains = parse_args(arg)
+
 -- Load saves
 local file, err = io.open(datapath.."advtrains", "r")
 local tbl = minetest.deserialize(file:read("*a"))
@@ -101,7 +127,9 @@ if type(tbl) ~= "table" then
 end
 if tbl.version then
 	advtrains.trains = tbl.trains
+	if not mappath then
 		advtrains.ndb.load_data(tbl.ndb)
+	end
 	
 else
 	error("Incompatible save format!")
@@ -112,6 +140,12 @@ file:close()
 
 local svgfile = io.open(datapath.."out.svg", "w")
 
+
+if mappath then
+	mapfile = io.open(mappath, "r")
+	cont = mapfile:read("*a"):sub(1, -7) -- remove </svg> end tag
+	svgfile:write(cont)
+else
 	svgfile:write([[
 <?xml version="1.0" standalone="no" ?>
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
@@ -122,11 +156,10 @@ svgfile:write([[
 
 	svgfile:write('viewBox="'..(-maxc)..' '..(-maxc)..' '..(2*maxc)..' '..(2*maxc)..'" >')
 
-
 	svgfile:write([[
 <circle cx="0" cy="0" r="5" stroke="red" stroke-width="1" />
 ]])
-
+end
 if wimg then
 	local wimx = -(wimresx*wimscale/2)
 	local wimy = -(wimresy*wimscale/2)
@@ -272,8 +305,11 @@ local function polyline_write(pl)
 end
 
 
+	
+
 -- while there are entries in the nodedb
 -- 1. find a starting point
+if not mappath then
 	local stpos, conns = advtrains.ndb.mapper_find_starting_point()
 	while stpos do
 		
@@ -301,24 +337,38 @@ while stpos do
 		end
 		stpos, conns = advtrains.ndb.mapper_find_starting_point()
 	end
-
+end
 -- draw trains
 trains = 0
+stopped = 0
+lines = {}
+running = {}
+if not no_trains then
 	for i,v in pairs(advtrains.trains) do
 		pos = v.last_pos
 		color = "green"
 		if v.velocity == 0 then
 			color = "orange"
+			stopped = stopped + 1
 		end
 		svgfile:write("<circle cx=\""..pos.x.."\" cy=\""..-pos.z.."\" r=\"3\" stroke=\""..color.."\" stroke-width=\"1\" fill=\"none\" />")
 		if v.line then
+			lines[v.line] = (lines[v.line] or 0) + 1
+			if v.velocity ~= 0 then
+				running[v.line] = (running[v.line] or 0) + 1
+			end
 			svgfile:write(" <text x=\""..(pos.x+5).."\" y=\""..-pos.z.."\" class=\"trainline\">"..v.line.."</text>")
 		end
 		trains = trains+1
 	end
+end
 
 svgfile:write("</svg>")
 svgfile:close()
 
 print("\nWrote",plcnt,"polylines. Processed", ndb_nodes_handled, "track,",ndb_nodes_notrack, "non-track nodes out of", ndb_nodes_total)
-print("Drew "..trains.." trains")
+print("Drew "..trains.." trains. "..stopped.." stopped trains.")
+print("\n Number of trains moving/total:")
+for i,v in pairs(lines) do
+	print(i..":            "..(running[i] or 0).."/"..v)
+end