Default: Destroy flammable items when in fire or lava

The check for igniters (fire/lava) will be performed every 10 secs
if the item is flammable.

if the item is found to be in lava it will then burn up and
disappear in a smoke puff.

If a non-lava igniter node is found, a combination of `flammable`
value of the item and `igniter` group value of the node will be used
to determine the chance for the item to be removed.

mods/default/README.txt

@@ -183,6 +183,10 @@ Pithydon (CC BY-SA 3.0)
   default_coral_orange.png
   default_coral_skeleton.png
 
+Ferk (CC0 1.0)
+  default_item_smoke.png
+  default_item_smoke.ogg, based on sound by http://opengameart.org/users/bart
+
 Glass breaking sounds (CC BY 3.0):
   1: http://www.freesound.org/people/cmusounddesign/sounds/71947/
   2: http://www.freesound.org/people/Tomlija/sounds/97669/

mods/default/init.lua

@@ -42,6 +42,7 @@ dofile(default_path.."/trees.lua")
 dofile(default_path.."/nodes.lua")
 dofile(default_path.."/furnace.lua")
 dofile(default_path.."/tools.lua")
+dofile(default_path.."/item_entity.lua")
 dofile(default_path.."/craftitems.lua")
 dofile(default_path.."/crafting.lua")
 dofile(default_path.."/mapgen.lua")

mods/default/item_entity.lua

@@ -0,0 +1,74 @@
+-- mods/default/item_entity.lua
+
+local builtin_item = minetest.registered_entities["__builtin:item"]
+
+local item = {
+	set_item = function(self, itemstring)
+		builtin_item.set_item(self, itemstring)
+
+		local stack = ItemStack(itemstring)
+		local itemdef = minetest.registered_items[stack:get_name()]
+		if itemdef and itemdef.groups.flammable ~= 0 then
+			self.flammable = itemdef.groups.flammable
+		end
+	end,
+
+	burn_up = function(self)
+		-- disappear in a smoke puff
+		self.object:remove()
+		local p = self.object:getpos()
+		minetest.sound_play("default_item_smoke", {
+			pos = p,
+			max_hear_distance = 8,
+		})
+		minetest.add_particlespawner({
+			amount = 3,
+			time = 0.1,
+			minpos = {x = p.x - 0.1, y = p.y + 0.1, z = p.z - 0.1 },
+			maxpos = {x = p.x + 0.1, y = p.y + 0.2, z = p.z + 0.1 },
+			minvel = {x = 0, y = 2.5, z = 0},
+			maxvel = {x = 0, y = 2.5, z = 0},
+			minacc = {x = -0.15, y = -0.02, z = -0.15},
+			maxacc = {x = 0.15, y = -0.01, z = 0.15},
+			minexptime = 4,
+			maxexptime = 6,
+			minsize = 5,
+			maxsize = 5,
+			collisiondetection = true,
+			texture = "default_item_smoke.png"
+		})
+	end,
+
+	on_step = function(self, dtime)
+		builtin_item.on_step(self, dtime)
+
+		if self.flammable then
+			-- flammable, check for igniters
+			self.ignite_timer = (self.ignite_timer or 0) + dtime
+			if self.ignite_timer > 10 then
+				self.ignite_timer = 0
+
+				local node = minetest.get_node_or_nil(self.object:getpos())
+				if not node then
+					return
+				end
+
+				-- Immediately burn up flammable items in lava
+				if minetest.get_item_group(node.name, "lava") > 0 then
+					self:burn_up()
+				else
+					--  otherwise there'll be a chance based on its igniter value
+					local burn_chance = self.flammable
+						* minetest.get_item_group(node.name, "igniter")
+					if burn_chance > 0 and math.random(0, burn_chance) ~= 0 then
+						self:burn_up()
+					end
+				end
+			end
+		end
+	end,
+}
+
+-- set defined item as new __builtin:item, with the old one as fallback table
+setmetatable(item, builtin_item)
+minetest.register_entity(":__builtin:item", item)