items can be put on walls with "POSTABLE" use_action

-can be put on "WALL" ter/furn
-update docs on how to add an iuse function
-tile layering supports ter/furn flag
-deduplicate ter/furn layer drawing

data/json/flags.json

@@ -591,6 +591,11 @@
     "type": "json_flag",
     "info": "You could probably <color_brown>plant</color> these."
   },
+  {
+    "id": "POSTABLE",
+    "type": "json_flag",
+    "info": "This item can be put up on a wall."
+  },
   {
     "id": "MELTS",
     "type": "json_flag",

data/json/item_actions.json

@@ -689,6 +689,11 @@
     "id": "PORTAL",
     "name": { "str": "Place" }
   },
+  {
+    "type": "item_action",
+    "id": "POSTABLE",
+    "name": { "str": "Put up" }
+  },
   {
     "type": "item_action",
     "id": "PROZAC",

data/json/items/armor/cloaks.json

@@ -16,6 +16,7 @@
     "material_thickness": 0.3,
     "environmental_protection": 1,
     "flags": [ "OVERSIZE", "BELTED", "ALLOWS_NATURAL_ATTACKS" ],
+    "use_action": [ "POSTABLE" ],
     "armor": [
       {
         "encumbrance": 50,

doc/DEVELOPER_FAQ.md

@@ -72,8 +72,9 @@ Specifically to ablative plates, some transform when damaged instead of damaging
 ## Adding an iuse function.
 
 1. Add the new item use code to `iuse.cpp` and `iuse.h`.
-2. Add the new json_flag to your item. And link it to the iuse function in `item_factory.cpp`.
-3. Document the new flag in `JSON_FLAGS.md`.
+2. Add a new json_flag to `flags.json`, and add the flag to your item(s) and to an `item_actions.json` entry. 
+3. Link the flag to the iuse function in `item_factory.cpp`.
+4. Document the new flag in `JSON_FLAGS.md`.
 
 ## Acid resistance
 

doc/JSON_FLAGS.md

@@ -832,6 +832,7 @@ These flags can be applied via JSON item definition to most items.  Not to be co
 - ```PAPER_SHAPED``` This item is shaped in form of thin paper sheet, and can be stored in leather journal.
 - ```PERFECT_LOCKPICK``` Item is a perfect lockpick.  Takes only 5 seconds to pick a lock and never fails, but using it grants only a small amount of lock picking xp.  The item should have `LOCKPICK` quality of at least 1.
 - ```PLANTABLE_SEED``` This item is a seed, and you can plant it.
+- ```POSTABLE``` This item can be placed on terrain/furniture with the WALL flag.
 - ```PRESERVE_SPAWN_OMT``` This item will store the OMT that it spawns in, in the `spawn_location_omt` item var.
 - ```PROVIDES_TECHNIQUES``` This item will provide martial arts techniques when worn/in the character's inventory, in addition to those provided by the weapon and martial art.
 - ```PSEUDO``` Used internally to mark items that are referred to in the crafting inventory but are not actually items.  They can be used as tools, but not as components.  Implies `TRADER_AVOID`.

src/cata_tiles.h

@@ -34,6 +34,7 @@ class JsonObject;
 class pixel_minimap;
 
 extern void set_displaybuffer_rendertarget();
+using ter_str_id = string_id<ter_t>;
 
 /** Structures */
 struct tile_type {

src/item_factory.cpp

@@ -1854,6 +1854,7 @@ void Item_factory::init()
     add_iuse( "POISON", &iuse::poison );
     add_iuse( "PORTABLE_GAME", &iuse::portable_game );
     add_iuse( "PORTAL", &iuse::portal );
+    add_iuse( "POSTABLE", &iuse::postable );
     add_iuse( "PROZAC", &iuse::prozac );
     add_iuse( "PURIFY_SMART", &iuse::purify_smart );
     add_iuse( "RADGLOVE", &iuse::radglove );

src/iuse.cpp

@@ -8811,6 +8811,31 @@ std::optional<int> iuse::disassemble( Character *p, item *it, const tripoint & )
     return 0;
 }
 
+std::optional<int> iuse::postable( Character *p, item *it, const tripoint & )
+{
+    map &here = get_map();
+
+    //arbitrary limit of 10 postable items per wall
+    const std::function<bool( const tripoint_bub_ms & )> f = [&here]( const tripoint_bub_ms & pnt ) {
+        return here.has_flag_ter_or_furn( ter_furn_flag::TFLAG_WALL, pnt ) && here.i_at( pnt ).size() < 10;
+    };
+
+    const std::optional<tripoint_bub_ms> pnt_ = choose_adjacent_highlight(
+                _( "Post to which wall?" ), _( "There is no applicable wall nearby." ), f, false );
+    if( !pnt_ ) {
+        return std::nullopt;
+    }
+
+    //copy and place used item and remove the used item from inventory
+    item_location original_item( *p, it );
+    item copy_item( *original_item );
+    here.add_item( *pnt_, copy_item );
+    original_item.remove_item();
+    p->add_msg_if_player( m_good, _( "You put up the %s." ), copy_item.tname() );
+
+    return 0;
+}
+
 std::optional<int> iuse::melatonin_tablet( Character *p, item *it, const tripoint & )
 {
     p->add_msg_if_player( _( "You pop a %s." ), it->tname() );

src/iuse.h

@@ -222,6 +222,8 @@ std::optional<int> craft( Character *, item *, const tripoint & );
 
 std::optional<int> disassemble( Character *, item *, const tripoint & );
 
+std::optional<int> postable( Character *, item *, const tripoint & );
+
 // Helper functions for other iuse functions
 void cut_log_into_planks( Character & );
 void play_music( Character *p, const tripoint &source, int volume, int max_morale,