From c009aa3a22b0a2d5790898ac05c92d429c82f94a Mon Sep 17 00:00:00 2001
From: Perttu Ahola <celeron55@gmail.com>
Date: Mon, 23 Jul 2012 20:41:40 +0300
Subject: [PATCH] Fix building on top of (pointable && buildable_to) nodes

---
 builtin/item.lua | 48 ++++++++++++++++++++++++++++++++++--------------
 src/game.cpp     |  7 +++++++
 2 files changed, 41 insertions(+), 14 deletions(-)

diff --git a/builtin/item.lua b/builtin/item.lua
index 5cd28303a..08b8d1c58 100644
--- a/builtin/item.lua
+++ b/builtin/item.lua
@@ -125,50 +125,70 @@ function minetest.item_place_node(itemstack, placer, pointed_thing)
 	local item = itemstack:peek_item()
 	local def = itemstack:get_definition()
 	if def.type == "node" and pointed_thing.type == "node" then
-		local pos = pointed_thing.above
-		local oldnode = minetest.env:get_node(pos)
-		local olddef = ItemStack({name=oldnode.name}):get_definition()
+		local under = pointed_thing.under
+		local oldnode_under = minetest.env:get_node(under)
+		local olddef_under = ItemStack({name=oldnode_under.name}):get_definition()
+		olddef_under = olddef_under or minetest.nodedef_default
+		local above = pointed_thing.above
+		local oldnode_above = minetest.env:get_node(above)
+		local olddef_above = ItemStack({name=oldnode_above.name}):get_definition()
+		olddef_above = olddef_above or minetest.nodedef_default
 
-		if not olddef.buildable_to then
+		if not olddef_above.buildable_to and not olddef_under.buildable_to then
 			minetest.log("info", placer:get_player_name() .. " tried to place"
-				.. " node in invalid position " .. minetest.pos_to_string(pos)
-				.. ", replacing " .. oldnode.name)
+				.. " node in invalid position " .. minetest.pos_to_string(above)
+				.. ", replacing " .. oldnode_above.name)
 			return
 		end
 
+		-- Place above pointed node
+		local place_to = {x = above.x, y = above.y, z = above.z}
+
+		-- If node under is buildable_to, place into it instead (eg. snow)
+		if olddef_under.buildable_to then
+			minetest.log("info", "node under is buildable to")
+			place_to = {x = under.x, y = under.y, z = under.z}
+		end
+
 		minetest.log("action", placer:get_player_name() .. " places node "
-			.. def.name .. " at " .. minetest.pos_to_string(pos))
+			.. def.name .. " at " .. minetest.pos_to_string(place_to))
 
 		local newnode = {name = def.name, param1 = 0, param2 = 0}
 
 		-- Calculate direction for wall mounted stuff like torches and signs
 		if def.paramtype2 == 'wallmounted' then
-			local under = pointed_thing.under
-			local above = pointed_thing.above
-			local dir = {x = under.x - above.x, y = under.y - above.y, z = under.z - above.z}
+			local dir = {
+				x = under.x - above.x,
+				y = under.y - above.y,
+				z = under.z - above.z
+			}
 			newnode.param2 = minetest.dir_to_wallmounted(dir)
 		-- Calculate the direction for furnaces and chests and stuff
 		elseif def.paramtype2 == 'facedir' then
 			local placer_pos = placer:getpos()
 			if placer_pos then
-				local dir = {x = pos.x - placer_pos.x, y = pos.y - placer_pos.y, z = pos.z - placer_pos.z}
+				local dir = {
+					x = above.x - placer_pos.x,
+					y = above.y - placer_pos.y,
+					z = above.z - placer_pos.z
+				}
 				newnode.param2 = minetest.dir_to_facedir(dir)
 				minetest.log("action", "facedir: " .. newnode.param2)
 			end
 		end
 
 		-- Add node and update
-		minetest.env:add_node(pos, newnode)
+		minetest.env:add_node(place_to, newnode)
 
 		-- Run callback
 		if def.after_place_node then
-			def.after_place_node(pos, placer)
+			def.after_place_node(place_to, placer)
 		end
 
 		-- Run script hook (deprecated)
 		local _, callback
 		for _, callback in ipairs(minetest.registered_on_placenodes) do
-			callback(pos, newnode, placer)
+			callback(place_to, newnode, placer)
 		end
 
 		itemstack:take_item()
diff --git a/src/game.cpp b/src/game.cpp
index 19c4707de..7d93e3db2 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -2304,6 +2304,13 @@ void the_game(
 								<<playeritem.name<<" is "
 								<<def.node_placement_prediction<<std::endl;
 						v3s16 p = neighbourpos;
+						// Place inside node itself if buildable_to
+						try{
+							MapNode n_under = map.getNode(nodepos);
+							if(nodedef->get(n_under).buildable_to)
+								p = nodepos;
+						}catch(InvalidPositionException &e){}
+						// Find id of predicted node
 						content_t id;
 						bool found =
 							nodedef->getId(def.node_placement_prediction, id);