Do not show item overlay if slot is occupied by item (bookshelf, vessels shelf)

mods/default/nodes.lua

@@ -1815,6 +1815,9 @@ local bookshelf_formspec =
 	"listring[current_player;main]" ..
 	default.get_hotbar_bg(0,2.85)
 
+local function get_bookshelf_formspec(inv)
+	local formspec = bookshelf_formspec
+	local invlist = inv and inv:get_list("books")
 	-- Inventory slots overlay
 	local bx, by = 0, 0.3
 	for i = 1, 16 do
@@ -1822,10 +1825,14 @@ for i = 1, 16 do
 			bx = 0
 			by = by + 1
 		end
-	bookshelf_formspec = bookshelf_formspec ..
+		if not invlist or invlist[i]:is_empty() then
+			formspec = formspec ..
 				"image[" .. bx .. "," .. by .. ";1,1;default_bookshelf_slot.png]"
+		end
 		bx = bx + 1
 	end
+	return formspec
+end
 
 minetest.register_node("default:bookshelf", {
 	description = "Bookshelf",
@@ -1838,7 +1845,7 @@ minetest.register_node("default:bookshelf", {
 
 	on_construct = function(pos)
 		local meta = minetest.get_meta(pos)
-		meta:set_string("formspec", bookshelf_formspec)
+		meta:set_string("formspec", get_bookshelf_formspec(nil))
 		local inv = meta:get_inventory()
 		inv:set_size("books", 8 * 2)
 	end,
@@ -1855,14 +1862,20 @@ minetest.register_node("default:bookshelf", {
 	on_metadata_inventory_move = function(pos, from_list, from_index, to_list, to_index, count, player)
 		minetest.log("action", player:get_player_name() ..
 			" moves stuff in bookshelf at " .. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_bookshelf_formspec(meta:get_inventory()))
 	end,
 	on_metadata_inventory_put = function(pos, listname, index, stack, player)
 		minetest.log("action", player:get_player_name() ..
 			" moves stuff to bookshelf at " .. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_bookshelf_formspec(meta:get_inventory()))
 	end,
 	on_metadata_inventory_take = function(pos, listname, index, stack, player)
 		minetest.log("action", player:get_player_name() ..
 			" takes stuff from bookshelf at " .. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_bookshelf_formspec(meta:get_inventory()))
 	end,
 	on_blast = function(pos)
 		local drops = {}

mods/vessels/init.lua

@@ -13,6 +13,9 @@ local vessels_shelf_formspec =
 	"listring[current_player;main]" ..
 	default.get_hotbar_bg(0, 2.85)
 
+local function get_vessels_shelf_formspec(inv)
+	local formspec = vessels_shelf_formspec
+	local invlist = inv and inv:get_list("vessels")
 	-- Inventory slots overlay
 	local vx, vy = 0, 0.3
 	for i = 1, 16 do
@@ -20,10 +23,14 @@ for i = 1, 16 do
 			vx = 0
 			vy = vy + 1
 		end
-	vessels_shelf_formspec = vessels_shelf_formspec ..
+		if not invlist or invlist[i]:is_empty() then
+			formspec = formspec ..
 				"image[" .. vx .. "," .. vy .. ";1,1;vessels_shelf_slot.png]"
+		end
 		vx = vx + 1
 	end
+	return formspec
+end
 
 minetest.register_node("vessels:shelf", {
 	description = "Vessels Shelf",
@@ -36,7 +43,7 @@ minetest.register_node("vessels:shelf", {
 
 	on_construct = function(pos)
 		local meta = minetest.get_meta(pos)
-		meta:set_string("formspec", vessels_shelf_formspec)
+		meta:set_string("formspec", get_vessels_shelf_formspec(nil))
 		local inv = meta:get_inventory()
 		inv:set_size("vessels", 8 * 2)
 	end,
@@ -53,14 +60,20 @@ minetest.register_node("vessels:shelf", {
 	on_metadata_inventory_move = function(pos, from_list, from_index, to_list, to_index, count, player)
 		minetest.log("action", player:get_player_name() ..
 			   " moves stuff in vessels shelf at ".. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_vessels_shelf_formspec(meta:get_inventory()))
 	end,
 	on_metadata_inventory_put = function(pos, listname, index, stack, player)
 		minetest.log("action", player:get_player_name() ..
 			   " moves stuff to vessels shelf at ".. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_vessels_shelf_formspec(meta:get_inventory()))
 	end,
 	on_metadata_inventory_take = function(pos, listname, index, stack, player)
 		minetest.log("action", player:get_player_name() ..
 			   " takes stuff from vessels shelf at ".. minetest.pos_to_string(pos))
+		local meta = minetest.get_meta(pos)
+		meta:set_string("formspec", get_vessels_shelf_formspec(meta:get_inventory()))
 	end,
 	on_blast = function(pos)
 		local drops = {}