add maximum length parameter to split_at_fc and split_off_locomotive

advtrains/trainlogic.lua

@@ -892,16 +892,21 @@ function advtrains.spawn_wagons(train_id)
 	end
 end
 
-function advtrains.split_train_at_fc(train, count_empty)
+function advtrains.split_train_at_fc(train, count_empty, length_limit)
 	-- splits train at first different current FC by convention,
 	-- locomotives have empty FC so are ignored
 	-- count_empty is used to split off locomotives
+	-- length_limit limits the length of the first train to length_limit wagons
 	local train_id = train.id
 	local fc = false
 	local ind = 0
 	for i = 1, #train.trainparts do
 		local w_id = train.trainparts[i]
 		local data = advtrains.wagons[w_id]
+		if length_limit and i > length_limit then
+			ind = i
+			break
+		end
 		if data then
 			local wfc = advtrains.get_cur_fc(data)
 			if  wfc ~= "" or count_empty then

advtrains_luaautomation/README.txt

@@ -203,21 +203,38 @@ set_rc(routingcode)
 split_at_index(index, command)
 	Splits the train at the specified index, into a train with index-1 wagons and a second train starting with the index-th wagon.
 	command specifies an atc command to be sent to the second train after decoupling.
-split_at_fc(command)
+split_at_fc(command, len)
 	Splits the train in such a way that all cars with non-empty
 	current FC of the first part of the train have the same FC. The
 	command specified is sent to the rear part, as with
 	split_at_index.  It returns the fc of the cars of the first part.
 
+	The optional argument len specifies the maximum length for the
+	first part of the train. Say, we have len=3, and the train has ""
+	"" "foo" "foo" "foo" "bar", then the first train part will be ""
+	"" "foo".
+
 	Example : Train has current FCs "" "" "foo" "bar" "foo"
 	Result: first train: "" "" "foo"; second train: "bar" "foo"
 	The command returns "foo" in this case
-split_off_locomotive(command)
+split_off_locomotive(command, len)
 	Splits off the locomotives at the front of the train, which are
 	identified by an empty FC.  command specifies the command to be
 	executed by the rear half of the train.
+
+	The optional argument len specifies the maximum length for the
+	first part of the train. Say, we have len=3, and the train has ""
+	"" "foo" "foo" "foo" "bar", then the first train part will be ""
+	"" "foo".	
 step_fc()
-	Steps the FCs of all train cars forward
+	Steps the FCs of all train cars forward. FCs are composed of codes
+	separated by exclamation marks (!), for instance
+	"foo!bar!baz". Each wagon has a current FC, indicating its next
+	destination. Stepping the freight code forward, selects the next
+	code after the !. If the end of the string is reached, then the
+	first code is selected, except if the string ends with a question
+	mark, then the order is reversed.
+
 train_length()
 	returns the number of cars the train is composed of
 set_autocouple()

advtrains_luaautomation/atc_rail.lua

@@ -66,19 +66,19 @@ function r.fire_event(pos, evtdata)
 			end
 			return false
 		end,
-		split_at_fc = function(cmd)
+		split_at_fc = function(cmd, len)
 			assertt(cmd, "string")
 			if not train_id then return false end
-			local new_id, fc = advtrains.split_train_at_fc(train)
+			local new_id, fc = advtrains.split_train_at_fc(train, false, len)
 			if new_id then
 				minetest.after(1,advtrains.atc.train_set_command,advtrains.trains[new_id], cmd, atc_arrow)
 			end
 			return fc or ""
 		end,
-		split_off_locomotive = function(cmd)
+		split_off_locomotive = function(cmd, len)
 			assertt(cmd, "string")
 			if not train_id then return false end
-			local new_id, fc = advtrains.split_train_at_fc(train, true)
+			local new_id, fc = advtrains.split_train_at_fc(train, true, len)
 			if new_id then
 				minetest.after(1,advtrains.atc.train_set_command,advtrains.trains[new_id], cmd, atc_arrow)
 			end