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

@@ -1,13 +1,19 @@
 -- 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},
+		animation = {type = "vertical_frames",
+			aspect_w = 16, aspect_h = 16, length = 1},
 	}},
 	inventory_image = "fire_basic_flame.png",
 	light_source = 14,
@@ -29,11 +35,18 @@ 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,
@@ -48,6 +61,9 @@ function fire.get_area_p0p1(pos)
 	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}
@@ -66,7 +82,8 @@ function fire.update_sounds_around(pos)
 	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 p0 = {x = pos.x - 1, y = pos.y, z = pos.z - 1}
-	local p1 = {x=pos.x+2, y=pos.y, z=pos.z+2}
+	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,
+	interval = 7,
-	chance = 2,
+	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
@@ -123,7 +153,12 @@ minetest.register_abm({
 	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"},
@@ -148,12 +183,15 @@ minetest.register_abm({
 		end
 	end,
 })
+--]]
+
 
 -- Remove flammable nodes and flame
+
 minetest.register_abm({
 	nodenames = {"fire:basic_flame"},
-	interval = 3,
+	interval = 5,
-	chance = 2,
+	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