Difference between revisions of "NodeMetaRef"

Latest revision as of 02:12, 7 March 2018

Redirect to:

MetaDataRef

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-The instance of a node in the world normally only contains the three values mentioned in "[[node|Nodes]]". However, it is possible to insert extra data into a
+#REDIRECT [[MetaDataRef]]
-node. It is called "node metadata".
-Metadata contains two things:
-* A key-value store
-* An inventory
-Some of the values in the key-value store are handled specially:
-* <code>formspec</code> — Defines a right-click inventory menu. See "[[formspec|Formspec]]".
-* <code>infotext</code> — Text shown on the screen when the node is pointed at
-Can be gotten via <source enclose="none">minetest.get_meta(pos)</source>.
-'''Warning''' all metadata is sent to client, don't store sensitive stuff here.
-== Methods ==
-* <source enclose="none">set_string(name, value)</source>
-* <source enclose="none">get_string(name)</source>
-* <source enclose="none">set_int(name, value)</source>
-* <source enclose="none">get_int(name)</source>
-* <source enclose="none">set_float(name, value)</source>
-* <source enclose="none">get_float(name)</source>
-* <source enclose="none">[NodeMetaRef]get_inventory()</source> — returns [[InvRef]]
-* <source enclose="none">[NodeMetaRef]to_table()</source> — returns <source enclose="none">nil</source> or <source enclose="none">{fields = {...}, inventory = {list1 = {}, ...}}</source>
-* <source enclose="none">from_table(nil</source> or <source enclose="none">{})</source>
-== Example ==
-<source>
-local meta = minetest.get_meta(pos)
-meta:set_string("formspec",
-        "invsize[8,9;]"..
-        "list[context;main;0,0;8,4;]"..
-        "list[current_player;main;0,5;8,4;]")
-meta:set_string("infotext", "Chest");
-local inv = meta:[NodeMetaRef]get_inventory()
-inv:set_size("main", 8*4)
-print(dump(meta:[NodeMetaRef]to_table()))
-meta:from_table({
-    inventory = {
-        main = {
-[1] = "default:dirt",
-[2] = "",
-[3] = "",
-[4] = "",
-[5] = "",
-[6] = "",
-[7] = "",
-[8] = "",
-[9] = "",
-[10] = "",
-[11] = "",
-[12] = "",
-[13] = "",
-[14] = "default:cobble",
-[15] = "",
-[16] = "",
-[17] = "",
-[18] = "",
-[19] = "",
-[20] = "default:cobble",
-[21] = "",
-[22] = "",
-[23] = "",
-[24] = "",
-[25] = "",
-[26] = "",
-[27] = "",
-[28] = "",
-[29] = "",
-[30] = "",
-[31] = "",
-[32] = ""}
-    },
-    fields = {
-        formspec = "invsize[8,9;]list[context;main;0,0;8,4;]list[current_player;main;0,5;8,4;]",
-        infotext = "Chest"
-    }
-})
-</source>
-== An excerpt from an e-mail between Minetest developers ==
-<pre>
-> When I attach a Lua table to a node I seem to have a
-> choice: to store things with many calls to
-> meta.set_int/meta.set_string etc. or via meta:from_table.
-> meta:from_table lets me store an arbitrary table under "fields":
->
-> local meta = minetest.get_meta(pos)
-> local mt = meta:to_table()
->
-> len = tonumber(mt.fields.length_remaining)
->
-> ... only I have noticed that every key under fields can only store
-> strings. So as a general purpose 'table' store, this is not so useful.
-> I came upon this because I wanted to store the initial position of a
-> node. This requires either:
->
-> meta:set_int('x', pos.x)
-> meta:set_int('y', pos.y)
-> meta:set_int('z', pos.z)
->
-> or something like:
->
-> mt.fields.tail_pos = "return {" .. pos.x .. "," .. pos.y .. "," .. pos.z .. "}"
->
-> and then something like this to read it back:
-> tail_pos = loadstring(mt.fields.tail_pos)()
->
->
-> ...correct? Or am I missing an obvious alternate solution? The api
-> docs are not detailed on this.
-Answer by celeron55:
-For simplicity, all the fields are internally strings, and don't store
-any type information. I can see the inconvenience though.
-You shouldn't use loadstring() directly, because then somebody could
-create a world which stores arbitrary Lua code, which can eg. remove
-all files, or something similar.
-For storing Lua variables with type information, you can use
-minetest.serialize() and minetest.deserialize(). They take any
-serializable Lua table, which can contain:
-- tables
-- strings
-- numbers
-- functions that don't access anything outside of what is stored in
-  the data itself and what is passed as a parameter))
-and make it into a string, and the other way around, and they
-will not execute any foreign code (unless you do certain
-complicated-ish stupid things, which probably won't happen).
-You can check out the implementation in builtin/serialize.lua.
-So if you want to store a position in the data of a node, you can use:
-  local pos = {x=this, y=and, z=that}
-  meta:set_string("tail_pos", minetest.serialize(pos))
-and
-  local pos = minetest.deserialize(meta:get_string("tail_pos")).
-Keep in mind though that that thing isn't very largely in use, and
-there might be unnoticed problems.
-</pre>
-[[Category:Objects]]

Difference between revisions of "NodeMetaRef"

Latest revision as of 02:12, 7 March 2018

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