Fire: Slow down fire spread and reduce lua load

Increase chance value of ABMs
Disable ignition from a distance
Only detect neighbouring extinguishing nodes
Fix code style issues and add comments

mods/fire/init.lua

@@ -1,17 +1,23 @@
 -- minetest/fire/init.lua
 
+-- Global namespace for functions
+
 fire = {}
 
+
+-- Register flame node
+
 minetest.register_node("fire:basic_flame", {
 	description = "Fire",
 	drawtype = "firelike",
 	tiles = {{
-		name="fire_basic_flame_animated.png",
-		animation={type="vertical_frames", aspect_w=16, aspect_h=16, length=1},
+		name = "fire_basic_flame_animated.png",
+		animation = {type = "vertical_frames",
+			aspect_w = 16, aspect_h = 16, length = 1},
 	}},
 	inventory_image = "fire_basic_flame.png",
 	light_source = 14,
-	groups = {igniter=2,dig_immediate=3},
+	groups = {igniter = 2, dig_immediate = 3},
 	drop = '',
 	walkable = false,
 	buildable_to = true,
@@ -29,44 +35,55 @@ minetest.register_node("fire:basic_flame", {
 	on_blast = function() end,
 })
 
-fire.D = 6
+
+-- Fire sounds table
 -- key: position hash of low corner of area
 -- value: {handle=sound handle, name=sound name}
 fire.sounds = {}
 
+
+-- Get sound area of position
+
+-- size of sound areas
+fire.D = 6
+
 function fire.get_area_p0p1(pos)
 	local p0 = {
-		x=math.floor(pos.x/fire.D)*fire.D,
-		y=math.floor(pos.y/fire.D)*fire.D,
-		z=math.floor(pos.z/fire.D)*fire.D,
+		x = math.floor(pos.x / fire.D) * fire.D,
+		y = math.floor(pos.y / fire.D) * fire.D,
+		z = math.floor(pos.z / fire.D) * fire.D,
 	}
 	local p1 = {
-		x=p0.x+fire.D-1,
-		y=p0.y+fire.D-1,
-		z=p0.z+fire.D-1
+		x = p0.x + fire.D - 1,
+		y = p0.y + fire.D - 1,
+		z = p0.z + fire.D - 1
 	}
 	return p0, p1
 end
 
+
+-- Update fire sounds in sound area of position
+
 function fire.update_sounds_around(pos)
 	local p0, p1 = fire.get_area_p0p1(pos)
-	local cp = {x=(p0.x+p1.x)/2, y=(p0.y+p1.y)/2, z=(p0.z+p1.z)/2}
+	local cp = {x = (p0.x + p1.x) / 2, y = (p0.y + p1.y) / 2, z = (p0.z + p1.z) / 2}
 	local flames_p = minetest.find_nodes_in_area(p0, p1, {"fire:basic_flame"})
 	--print("number of flames at "..minetest.pos_to_string(p0).."/"
 	--		..minetest.pos_to_string(p1)..": "..#flames_p)
 	local should_have_sound = (#flames_p > 0)
 	local wanted_sound = nil
 	if #flames_p >= 9 then
-		wanted_sound = {name="fire_large", gain=1.5}
+		wanted_sound = {name = "fire_large", gain = 1.5}
 	elseif #flames_p > 0 then
-		wanted_sound = {name="fire_small", gain=1.5}
+		wanted_sound = {name = "fire_small", gain = 1.5}
 	end
 	local p0_hash = minetest.hash_node_position(p0)
 	local sound = fire.sounds[p0_hash]
 	if not sound then
 		if should_have_sound then
 			fire.sounds[p0_hash] = {
-				handle = minetest.sound_play(wanted_sound, {pos=cp, max_hear_distance = 16, loop=true}),
+				handle = minetest.sound_play(wanted_sound,
+					{pos = cp, max_hear_distance = 16, loop = true}),
 				name = wanted_sound.name,
 			}
 		end
@@ -77,40 +94,53 @@ function fire.update_sounds_around(pos)
 		elseif sound.name ~= wanted_sound.name then
 			minetest.sound_stop(sound.handle)
 			fire.sounds[p0_hash] = {
-				handle = minetest.sound_play(wanted_sound, {pos=cp, max_hear_distance = 16, loop=true}),
+				handle = minetest.sound_play(wanted_sound,
+					{pos = cp, max_hear_distance = 16, loop = true}),
 				name = wanted_sound.name,
 			}
 		end
 	end
 end
 
+
+-- Update fire sounds on flame node construct or destruct
+
 function fire.on_flame_add_at(pos)
 	fire.update_sounds_around(pos)
 end
 
+
 function fire.on_flame_remove_at(pos)
 	fire.update_sounds_around(pos)
 end
 
+
+-- Return positions for flames around a burning node
+
 function fire.find_pos_for_flame_around(pos)
 	return minetest.find_node_near(pos, 1, {"air"})
 end
 
+
+-- Detect nearby extinguishing nodes
+
 function fire.flame_should_extinguish(pos)
 	if minetest.setting_getbool("disable_fire") then return true end
 	--return minetest.find_node_near(pos, 1, {"group:puts_out_fire"})
-	local p0 = {x=pos.x-2, y=pos.y, z=pos.z-2}
-	local p1 = {x=pos.x+2, y=pos.y, z=pos.z+2}
+	local p0 = {x = pos.x - 1, y = pos.y, z = pos.z - 1}
+	local p1 = {x = pos.x + 1, y = pos.y + 1, z = pos.z + 1}
 	local ps = minetest.find_nodes_in_area(p0, p1, {"group:puts_out_fire"})
 	return (#ps ~= 0)
 end
 
+
 -- Ignite neighboring nodes
+
 minetest.register_abm({
 	nodenames = {"group:flammable"},
 	neighbors = {"group:igniter"},
-	interval = 5,
-	chance = 2,
+	interval = 7,
+	chance = 32,
 	action = function(p0, node, _, _)
 		-- If there is water or stuff like that around flame, don't ignite
 		if fire.flame_should_extinguish(p0) then
@@ -118,12 +148,17 @@ minetest.register_abm({
 		end
 		local p = fire.find_pos_for_flame_around(p0)
 		if p then
-			minetest.set_node(p, {name="fire:basic_flame"})
+			minetest.set_node(p, {name = "fire:basic_flame"})
 		end
 	end,
 })
 
+
 -- Rarely ignite things from far
+
+--[[ Currently disabled to reduce the chance of uncontrollable spreading
+	fires that disrupt servers. Also for less lua processing load.
+
 minetest.register_abm({
 	nodenames = {"group:igniter"},
 	neighbors = {"air"},
@@ -143,17 +178,20 @@ minetest.register_abm({
 			end
 			local p2 = fire.find_pos_for_flame_around(p)
 			if p2 then
-				minetest.set_node(p2, {name="fire:basic_flame"})
+				minetest.set_node(p2, {name = "fire:basic_flame"})
 			end
 		end
 	end,
 })
+--]]
+
 
 -- Remove flammable nodes and flame
+
 minetest.register_abm({
 	nodenames = {"fire:basic_flame"},
-	interval = 3,
-	chance = 2,
+	interval = 5,
+	chance = 16,
 	action = function(p0, node, _, _)
 		-- If there is water or stuff like that around flame, remove flame
 		if fire.flame_should_extinguish(p0) then
@@ -161,7 +199,7 @@ minetest.register_abm({
 			return
 		end
 		-- Make the following things rarer
-		if math.random(1,3) == 1 then
+		if math.random(1, 3) == 1 then
 			return
 		end
 		-- If there are no flammable nodes around flame, remove flame
@@ -169,7 +207,7 @@ minetest.register_abm({
 			minetest.remove_node(p0)
 			return
 		end
-		if math.random(1,4) == 1 then
+		if math.random(1, 4) == 1 then
 			-- remove a flammable node around flame
 			local p = minetest.find_node_near(p0, 1, {"group:flammable"})
 			if p then