Add lag mitigation

All messages sent to the displays are firstr enqueued, then "played
back" on globalstep, similar to biome_lib's deferred-generation method.

By default, no more than 10 messages will be added to the queue.  If the
queue should exceed that, old messages will be deleted to make room for
new messages.

Messages will be pulled from the queue, one item per server tick, in the
order received, and relayed to their displays, if dtime <= 0.2s.  If
dtime is greater, messages will be withheld until it decreases.

Autoscroll now limits the speed to 0.5s per step.

init.lua

@@ -2,6 +2,13 @@
 -- by Vanessa Dannenberg
 
 led_marquee = {}
+led_marquee.scheduled_messages = {}
+
+led_marquee.message_minimum_time   = tonumber(minetest.settings:get("led_marquee_message_minimum_time"))   or 0.5
+
+led_marquee.message_schedule_dtime = tonumber(minetest.settings:get("led_marquee_message_schedule_dtime")) or 0.2
+led_marquee.message_schedule_size  = tonumber(minetest.settings:get("led_marquee_message_schedule_size"))  or 10
+led_marquee.relay_timer = 0
 
 local S
 if minetest.get_modpath("intllib") then
@@ -148,7 +155,7 @@ end
 led_marquee.set_timer = function(pos, timeout)
 	local timer = minetest.get_node_timer(pos)
 	timer:stop()
-	if not timeout or timeout < 0.2 or timeout > 5 then return false end
+	if not timeout or timeout < led_marquee.message_minimum_time or timeout > 5 then return false end
 
 	if timeout > 0 then
 		local meta = minetest.get_meta(pos)
@@ -189,7 +196,7 @@ led_marquee.scroll_text = function(pos, elapsed, skip)
 			break
 		end
 	end
-	led_marquee.display_msg(pos, channel, "/"..colorchar..string.sub(msg, f)..string.rep(" ", skip + 1))
+	led_marquee.schedule_msg(pos, channel, "/"..colorchar..string.sub(msg, f)..string.rep(" ", skip + 1))
 
 	meta:set_int("index", f)
 	if not elapsed or elapsed < 0.2 then return false end
@@ -218,6 +225,27 @@ led_marquee.decode_color = function(msg)
 
 end
 
+minetest.register_globalstep(function(dtime)
+	if dtime <= led_marquee.message_schedule_dtime
+	  and (#led_marquee.scheduled_messages) > 0 then
+		led_marquee.display_msg(
+			led_marquee.scheduled_messages[1].pos,
+			led_marquee.scheduled_messages[1].channel,
+			led_marquee.scheduled_messages[1].msg
+		)
+	end
+	table.remove(led_marquee.scheduled_messages, 1)
+end)
+
+led_marquee.schedule_msg = function(pos, channel, msg)
+	local idx = #led_marquee.scheduled_messages
+	led_marquee.scheduled_messages[idx+1] = { pos=pos, channel=channel, msg=msg }
+
+	if idx >= led_marquee.message_schedule_size then
+		table.remove(led_marquee.scheduled_messages, 1)
+	end
+end
+
 led_marquee.display_msg = function(pos, channel, msg)
 	msg = string.sub(msg, 1, 6144).." "
 	if string.sub(msg,1,1) == string.char(255) then -- treat it as incoming UTF-8
@@ -317,13 +345,13 @@ local on_digiline_receive_string = function(pos, node, channel, msg)
 				led_marquee.set_timer(pos, 0)
 				msg = string.rep(" ", 2048)
 				meta:set_string("last_msg", msg)
-				led_marquee.display_msg(pos, channel, msg)
+				led_marquee.schedule_msg(pos, channel, msg)
 				meta:set_int("index", 1)
 			elseif msg == "allon" then
 				led_marquee.set_timer(pos, 0)
 				msg = string.rep(string.char(144), 2048)
 				meta:set_string("last_msg", msg)
-				led_marquee.display_msg(pos, channel, msg)
+				led_marquee.schedule_msg(pos, channel, msg)
 				meta:set_int("index", 1)
 			elseif msg == "start_scroll" then
 				local timeout = meta:get_int("timeout")
@@ -333,7 +361,7 @@ local on_digiline_receive_string = function(pos, node, channel, msg)
 				return
 			elseif string.sub(msg, 1, 12) == "scroll_speed" then
 				local timeout = tonumber(string.sub(msg, 13))
-				led_marquee.set_timer(pos, timeout)
+				led_marquee.set_timer(pos, math.max(timeout, led_marquee.message_minimum_time))
 			elseif string.sub(msg, 1, 11) == "scroll_step" then
 				local skip = tonumber(string.sub(msg, 12))
 				led_marquee.scroll_text(pos, nil, skip)
@@ -348,7 +376,7 @@ local on_digiline_receive_string = function(pos, node, channel, msg)
 				led_marquee.set_timer(pos, 0)
 				local last_msg = meta:get_string("last_msg")
 				meta:set_string("last_msg", msg)
-				led_marquee.display_msg(pos, channel, msg)
+				led_marquee.schedule_msg(pos, channel, msg)
 				if last_msg ~= msg then
 					meta:set_int("index", 1)
 				end
@@ -363,7 +391,7 @@ local on_digiline_receive_string = function(pos, node, channel, msg)
 		end
 	elseif msg and type(msg) == "number" then
 		meta:set_string("last_msg", tostring(msg))
-		led_marquee.display_msg(pos, channel, tostring(msg))
+		led_marquee.schedule_msg(pos, channel, tostring(msg))
 		meta:set_int("index", 1)
 	end
 end