Nodebox: Allow nodeboxes to "connect"

We introduce a new nodebox type "connected", and allow these nodes to
have optional nodeboxes that connect it to other connecting nodeboxes.

This is all done at scenedraw time in the client. The client will
inspect the surrounding nodes and if they are to be connected to,
it will draw the appropriate connecting nodeboxes to make those
connections.

In the node_box definition, we have to specify separate nodeboxes for
each valid connection. This allows us to make nodes that connect only
horizontally (the common case) by providing optional nodeboxes for +x,
-x, +z, -z directions. Or this allows us to make wires that can connect
up and down, by providing nodeboxes that connect it up and down (+y,
-y) as well.

The optional nodeboxes can be arrays. They are named "connect_top,
"connect_bottom", "connect_front", "connect_left", "connect_back" and
"connect_right". Here, "front" means the south facing side of the node
that has facedir = 0.

Additionally, a "fixed" nodebox list present will always be drawn,
so one can make a central post, for instance. This "fixed" nodebox
can be omitted, or it can be an array of nodeboxes.

Collision boxes are also updated in exactly the same fashion, which
allows you to walk over the upper extremities of the individual
node boxes, or stand really close to them. You can also walk up
node noxes that are small in height, all as expected, and unlike the
NDT_FENCELIKE nodes.

I've posted a screenshot demonstrating the flexibility at
    http://i.imgur.com/zaJq8jo.png
In the screenshot, all connecting nodes are of this new subtype.

Transparent textures render incorrectly, Which I don't think is
related to this text, as other nodeboxes also have issues with this.

A protocol bump is performed in order to be able to send older clients
a nodeblock that is usable for them. In order to avoid abuse of users
we send older clients a "full-size" node, so that it's impossible for
them to try and walk through a fence or wall that's created in this
fashion. This was tested with a pre-bump client connected against a
server running the new protocol.

These nodes connect to other nodes, and you can select which ones
those are by specifying node names (or group names) in the
connects_to string array:
      connects_to = { "group:fence", "default:wood" }
By default, nodes do not connect to anything, allowing you to create
nodes that always have to be paired in order to connect. lua_api.txt
is updated to reflect the extension to the node_box API.

Example lua code needed to generate these nodes can be found here:
    https://gist.github.com/sofar/b381c8c192c8e53e6062

13 files changed, 335 insertions, 53 deletions

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index e2ab65ddc..f51c950c3 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -617,6 +617,18 @@ A nodebox is defined as any of:
         wall_bottom = box,
         wall_side = box
     }
+    {
+        -- A node that has optional boxes depending on neighbouring nodes'
+        -- presence and type. See also `connects_to`.
+        type = "connected",
+        fixed = box OR {box1, box2, ...}
+        connect_top = box OR {box1, box2, ...}
+        connect_bottom = box OR {box1, box2, ...}
+        connect_front = box OR {box1, box2, ...}
+        connect_left = box OR {box1, box2, ...}
+        connect_back = box OR {box1, box2, ...}
+        connect_right = box OR {box1, box2, ...}
+    }
 
 A `box` is defined as:
 
@@ -3461,6 +3473,10 @@ Definition tables
         light_source = 0, -- Amount of light emitted by node
         damage_per_second = 0, -- If player is inside node, this damage is caused
         node_box = {type="regular"}, -- See "Node boxes"
+        connects_to = nodenames, --[[
+        * Used for nodebox nodes with the type == "connected"
+        * Specifies to what neighboring nodes connections will be drawn
+        * e.g. `{"group:fence", "default:wood"}` or `"default:stone"` ]]
         mesh = "model",
         selection_box = {type="regular"}, -- See "Node boxes" --[[
         ^ If drawtype "nodebox" is used and selection_box is nil, then node_box is used. ]]
diff --git a/src/collision.cpp b/src/collision.cpp
index d847f6297..a3979f1dc 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -185,6 +185,13 @@ bool wouldCollideWithCeiling(
 	return false;
 }
 
+static inline void getNeighborConnectingFace(v3s16 p, INodeDefManager *nodedef,
+		Map *map, MapNode n, int v, int *neighbors)
+{
+	MapNode n2 = map->getNodeNoEx(p);
+	if (nodedef->nodeboxConnects(n, n2))
+		*neighbors |= v;
+}
 
 collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		f32 pos_max_d, const aabb3f &box_0,
@@ -261,12 +268,41 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 			// Object collides into walkable nodes
 
 			any_position_valid = true;
-			const ContentFeatures &f = gamedef->getNodeDefManager()->get(n);
+			INodeDefManager *nodedef = gamedef->getNodeDefManager();
+			const ContentFeatures &f = nodedef->get(n);
 			if(f.walkable == false)
 				continue;
 			int n_bouncy_value = itemgroup_get(f.groups, "bouncy");
 
-			std::vector<aabb3f> nodeboxes = n.getCollisionBoxes(gamedef->ndef());
+			int neighbors = 0;
+			if (f.drawtype == NDT_NODEBOX && f.node_box.type == NODEBOX_CONNECTED) {
+				v3s16 p2 = p;
+
+				p2.Y++;
+				getNeighborConnectingFace(p2, nodedef, map, n, 1, &neighbors);
+
+				p2 = p;
+				p2.Y--;
+				getNeighborConnectingFace(p2, nodedef, map, n, 2, &neighbors);
+
+				p2 = p;
+				p2.Z--;
+				getNeighborConnectingFace(p2, nodedef, map, n, 4, &neighbors);
+
+				p2 = p;
+				p2.X--;
+				getNeighborConnectingFace(p2, nodedef, map, n, 8, &neighbors);
+
+				p2 = p;
+				p2.Z++;
+				getNeighborConnectingFace(p2, nodedef, map, n, 16, &neighbors);
+
+				p2 = p;
+				p2.X++;
+				getNeighborConnectingFace(p2, nodedef, map, n, 32, &neighbors);
+			}
+			std::vector<aabb3f> nodeboxes;
+			n.getCollisionBoxes(gamedef->ndef(), &nodeboxes, neighbors);
 			for(std::vector<aabb3f>::iterator
 					i = nodeboxes.begin();
 					i != nodeboxes.end(); ++i)
diff --git a/src/content_mapblock.cpp b/src/content_mapblock.cpp
index c15b9c424..c2934f26a 100644
--- a/src/content_mapblock.cpp
+++ b/src/content_mapblock.cpp
@@ -163,6 +163,14 @@ void makeCuboid(MeshCollector *collector, const aabb3f &box,
 	}
 }
 
+static inline void getNeighborConnectingFace(v3s16 p, INodeDefManager *nodedef,
+		MeshMakeData *data, MapNode n, int v, int *neighbors)
+{
+	MapNode n2 = data->m_vmanip.getNodeNoEx(p);
+	if (nodedef->nodeboxConnects(n, n2))
+		*neighbors |= v;
+}
+
 /*
 	TODO: Fix alpha blending for special nodes
 	Currently only the last element rendered is blended correct
@@ -1501,7 +1509,38 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 
 			v3f pos = intToFloat(p, BS);
 
-			std::vector<aabb3f> boxes = n.getNodeBoxes(nodedef);
+			int neighbors = 0;
+
+			// locate possible neighboring nodes to connect to
+			if (f.node_box.type == NODEBOX_CONNECTED) {
+				v3s16 p2 = p;
+
+				p2.Y++;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 1, &neighbors);
+
+				p2 = p;
+				p2.Y--;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 2, &neighbors);
+
+				p2 = p;
+				p2.Z--;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 4, &neighbors);
+
+				p2 = p;
+				p2.X--;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 8, &neighbors);
+
+				p2 = p;
+				p2.Z++;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 16, &neighbors);
+
+				p2 = p;
+				p2.X++;
+				getNeighborConnectingFace(blockpos_nodes + p2, nodedef, data, n, 32, &neighbors);
+			}
+
+			std::vector<aabb3f> boxes;
+			n.getNodeBoxes(nodedef, &boxes, neighbors);
 			for(std::vector<aabb3f>::iterator
 					i = boxes.begin();
 					i != boxes.end(); ++i)
diff --git a/src/game.cpp b/src/game.cpp
index c6125dd43..be4c46bc3 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -358,7 +358,9 @@ PointedThing getPointedThing(Client *client, Hud *hud, const v3f &player_positio
 				if (!isPointableNode(n, client, liquids_pointable)) {
 					continue;
 				}
-				std::vector<aabb3f> boxes = n.getSelectionBoxes(nodedef);
+
+				std::vector<aabb3f> boxes;
+				n.getSelectionBoxes(nodedef, &boxes);
 
 				v3s16 np(x, y, z);
 				v3f npf = intToFloat(np, BS);
@@ -389,7 +391,8 @@ PointedThing getPointedThing(Client *client, Hud *hud, const v3f &player_positio
 		f32 d = 0.001 * BS;
 		MapNode n = map.getNodeNoEx(pointed_pos);
 		v3f npf = intToFloat(pointed_pos, BS);
-		std::vector<aabb3f> boxes = n.getSelectionBoxes(nodedef);
+		std::vector<aabb3f> boxes;
+		n.getSelectionBoxes(nodedef, &boxes);
 		f32 face_min_distance = 1000 * BS;
 		for (std::vector<aabb3f>::const_iterator
 				i = boxes.begin();
diff --git a/src/localplayer.cpp b/src/localplayer.cpp
index 524c6272e..0c94582aa 100644
--- a/src/localplayer.cpp
+++ b/src/localplayer.cpp
@@ -310,7 +310,8 @@ void LocalPlayer::move(f32 dtime, Environment *env, f32 pos_max_d,
 		if (sneak_node_found) {
 			f32 cb_max = 0;
 			MapNode n = map->getNodeNoEx(m_sneak_node);
-			std::vector<aabb3f> nodeboxes = n.getCollisionBoxes(nodemgr);
+			std::vector<aabb3f> nodeboxes;
+			n.getCollisionBoxes(nodemgr, &nodeboxes);
 			for (std::vector<aabb3f>::iterator it = nodeboxes.begin();
 					it != nodeboxes.end(); ++it) {
 				aabb3f box = *it;
diff --git a/src/mapnode.cpp b/src/mapnode.cpp
index 671e949f1..a54658873 100644
--- a/src/mapnode.cpp
+++ b/src/mapnode.cpp
@@ -214,12 +214,12 @@ void MapNode::rotateAlongYAxis(INodeDefManager *nodemgr, Rotation rot)
 	}
 }
 
-static std::vector<aabb3f> transformNodeBox(const MapNode &n,
-		const NodeBox &nodebox, INodeDefManager *nodemgr)
+void transformNodeBox(const MapNode &n, const NodeBox &nodebox,
+		INodeDefManager *nodemgr, std::vector<aabb3f> *p_boxes, u8 neighbors = 0)
 {
-	std::vector<aabb3f> boxes;
-	if(nodebox.type == NODEBOX_FIXED || nodebox.type == NODEBOX_LEVELED)
-	{
+	std::vector<aabb3f> &boxes = *p_boxes;
+
+	if (nodebox.type == NODEBOX_FIXED || nodebox.type == NODEBOX_LEVELED) {
 		const std::vector<aabb3f> &fixed = nodebox.fixed;
 		int facedir = n.getFaceDir(nodemgr);
 		u8 axisdir = facedir>>2;
@@ -395,32 +395,71 @@ static std::vector<aabb3f> transformNodeBox(const MapNode &n,
 			boxes.push_back(box);
 		}
 	}
+	else if (nodebox.type == NODEBOX_CONNECTED)
+	{
+		size_t boxes_size = boxes.size();
+		boxes_size += nodebox.fixed.size();
+		if (neighbors & 1)
+			boxes_size += nodebox.connect_top.size();
+		if (neighbors & 2)
+			boxes_size += nodebox.connect_bottom.size();
+		if (neighbors & 4)
+			boxes_size += nodebox.connect_front.size();
+		if (neighbors & 8)
+			boxes_size += nodebox.connect_left.size();
+		if (neighbors & 16)
+			boxes_size += nodebox.connect_back.size();
+		if (neighbors & 32)
+			boxes_size += nodebox.connect_right.size();
+		boxes.reserve(boxes_size);
+
+#define BOXESPUSHBACK(c) do { \
+		for (std::vector<aabb3f>::const_iterator \
+				it = (c).begin(); \
+				it != (c).end(); ++it) \
+			(boxes).push_back(*it); \
+		} while (0)
+
+		BOXESPUSHBACK(nodebox.fixed);
+
+		if (neighbors & 1)
+			BOXESPUSHBACK(nodebox.connect_top);
+		if (neighbors & 2)
+			BOXESPUSHBACK(nodebox.connect_bottom);
+		if (neighbors & 4)
+			BOXESPUSHBACK(nodebox.connect_front);
+		if (neighbors & 8)
+			BOXESPUSHBACK(nodebox.connect_left);
+		if (neighbors & 16)
+			BOXESPUSHBACK(nodebox.connect_back);
+		if (neighbors & 32)
+			BOXESPUSHBACK(nodebox.connect_right);
+	}
 	else // NODEBOX_REGULAR
 	{
 		boxes.push_back(aabb3f(-BS/2,-BS/2,-BS/2,BS/2,BS/2,BS/2));
 	}
-	return boxes;
 }
 
-std::vector<aabb3f> MapNode::getNodeBoxes(INodeDefManager *nodemgr) const
+void MapNode::getNodeBoxes(INodeDefManager *nodemgr, std::vector<aabb3f> *boxes, u8 neighbors)
 {
 	const ContentFeatures &f = nodemgr->get(*this);
-	return transformNodeBox(*this, f.node_box, nodemgr);
+	transformNodeBox(*this, f.node_box, nodemgr, boxes, neighbors);
 }
 
-std::vector<aabb3f> MapNode::getCollisionBoxes(INodeDefManager *nodemgr) const
+void MapNode::getCollisionBoxes(INodeDefManager *nodemgr, std::vector<aabb3f> *boxes, u8 neighbors)
 {
 	const ContentFeatures &f = nodemgr->get(*this);
 	if (f.collision_box.fixed.empty())
-		return transformNodeBox(*this, f.node_box, nodemgr);
+		transformNodeBox(*this, f.node_box, nodemgr, boxes, neighbors);
 	else
-		return transformNodeBox(*this, f.collision_box, nodemgr);
+		transformNodeBox(*this, f.collision_box, nodemgr, boxes, neighbors);
 }
 
-std::vector<aabb3f> MapNode::getSelectionBoxes(INodeDefManager *nodemgr) const
+void MapNode::getSelectionBoxes(INodeDefManager *nodemgr, std::vector<aabb3f> *boxes)
 {
 	const ContentFeatures &f = nodemgr->get(*this);
-	return transformNodeBox(*this, f.selection_box, nodemgr);
+	transformNodeBox(*this, f.selection_box, nodemgr, boxes);
 }
 
 u8 MapNode::getMaxLevel(INodeDefManager *nodemgr) const
diff --git a/src/mapnode.h b/src/mapnode.h
index 7cc25c60c..4db888616 100644
--- a/src/mapnode.h
+++ b/src/mapnode.h
@@ -240,17 +240,17 @@ struct MapNode
 	/*
 		Gets list of node boxes (used for rendering (NDT_NODEBOX))
 	*/
-	std::vector<aabb3f> getNodeBoxes(INodeDefManager *nodemgr) const;
+	void getNodeBoxes(INodeDefManager *nodemgr, std::vector<aabb3f> *boxes, u8 neighbors = 0);
 
 	/*
 		Gets list of selection boxes
 	*/
-	std::vector<aabb3f> getSelectionBoxes(INodeDefManager *nodemgr) const;
+	void getSelectionBoxes(INodeDefManager *nodemg, std::vector<aabb3f> *boxes);
 
 	/*
 		Gets list of collision boxes
 	*/
-	std::vector<aabb3f> getCollisionBoxes(INodeDefManager *nodemgr) const;
+	void getCollisionBoxes(INodeDefManager *nodemgr, std::vector<aabb3f> *boxes, u8 neighbors = 0);
 
 	/*
 		Liquid helpers
diff --git a/src/network/networkprotocol.h b/src/network/networkprotocol.h
index dc15326d9..7cde6d764 100644
--- a/src/network/networkprotocol.h
+++ b/src/network/networkprotocol.h
@@ -135,6 +135,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 	PROTOCOL_VERSION 27:
 		backface_culling: backwards compatibility for playing with
 		newer client on pre-27 servers.
+		Add nodedef v3 - connected nodeboxes
 */
 
 #define LATEST_PROTOCOL_VERSION 27
diff --git a/src/nodedef.cpp b/src/nodedef.cpp
index ba9b4abf2..85cd848ae 100644
--- a/src/nodedef.cpp
+++ b/src/nodedef.cpp
@@ -33,6 +33,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "exceptions.h"
 #include "debug.h"
 #include "gamedef.h"
+#include "mapnode.h"
 #include <fstream> // Used in applyTextureOverrides()
 
 /*
@@ -48,44 +49,91 @@ void NodeBox::reset()
 	wall_top = aabb3f(-BS/2, BS/2-BS/16., -BS/2, BS/2, BS/2, BS/2);
 	wall_bottom = aabb3f(-BS/2, -BS/2, -BS/2, BS/2, -BS/2+BS/16., BS/2);
 	wall_side = aabb3f(-BS/2, -BS/2, -BS/2, -BS/2+BS/16., BS/2, BS/2);
+	// no default for other parts
+	connect_top.clear();
+	connect_bottom.clear();
+	connect_front.clear();
+	connect_left.clear();
+	connect_back.clear();
+	connect_right.clear();
 }
 
 void NodeBox::serialize(std::ostream &os, u16 protocol_version) const
 {
-	int version = protocol_version >= 21 ? 2 : 1;
+	int version = 1;
+	if (protocol_version >= 27)
+		version = 3;
+	else if (protocol_version >= 21)
+		version = 2;
 	writeU8(os, version);
 
-	if (version == 1 && type == NODEBOX_LEVELED)
-		writeU8(os, NODEBOX_FIXED);
-	else
-		writeU8(os, type);
+	switch (type) {
+	case NODEBOX_LEVELED:
+	case NODEBOX_FIXED:
+		if (version == 1)
+			writeU8(os, NODEBOX_FIXED);
+		else
+			writeU8(os, type);
 
-	if(type == NODEBOX_FIXED || type == NODEBOX_LEVELED)
-	{
 		writeU16(os, fixed.size());
-		for(std::vector<aabb3f>::const_iterator
+		for (std::vector<aabb3f>::const_iterator
 				i = fixed.begin();
 				i != fixed.end(); ++i)
 		{
 			writeV3F1000(os, i->MinEdge);
 			writeV3F1000(os, i->MaxEdge);
 		}
-	}
-	else if(type == NODEBOX_WALLMOUNTED)
-	{
+		break;
+	case NODEBOX_WALLMOUNTED:
+		writeU8(os, type);
+
 		writeV3F1000(os, wall_top.MinEdge);
 		writeV3F1000(os, wall_top.MaxEdge);
 		writeV3F1000(os, wall_bottom.MinEdge);
 		writeV3F1000(os, wall_bottom.MaxEdge);
 		writeV3F1000(os, wall_side.MinEdge);
 		writeV3F1000(os, wall_side.MaxEdge);
+		break;
+	case NODEBOX_CONNECTED:
+		if (version <= 2) {
+			// send old clients nodes that can't be walked through
+			// to prevent abuse
+			writeU8(os, NODEBOX_FIXED);
+
+			writeU16(os, 1);
+			writeV3F1000(os, v3f(-BS/2, -BS/2, -BS/2));
+			writeV3F1000(os, v3f(BS/2, BS/2, BS/2));
+		} else {
+			writeU8(os, type);
+
+#define WRITEBOX(box) do { \
+		writeU16(os, (box).size()); \
+		for (std::vector<aabb3f>::const_iterator \
+				i = (box).begin(); \
+				i != (box).end(); ++i) { \
+			writeV3F1000(os, i->MinEdge); \
+			writeV3F1000(os, i->MaxEdge); \
+		}; } while (0)
+
+			WRITEBOX(fixed);
+			WRITEBOX(connect_top);
+			WRITEBOX(connect_bottom);
+			WRITEBOX(connect_front);
+			WRITEBOX(connect_left);
+			WRITEBOX(connect_back);
+			WRITEBOX(connect_right);
+		}
+		break;
+	default:
+		writeU8(os, type);
+		break;
 	}
 }
 
 void NodeBox::deSerialize(std::istream &is)
 {
 	int version = readU8(is);
-	if(version < 1 || version > 2)
+	if (version < 1 || version > 3)
 		throw SerializationError("unsupported NodeBox version");
 
 	reset();
@@ -112,6 +160,26 @@ void NodeBox::deSerialize(std::istream &is)
 		wall_side.MinEdge = readV3F1000(is);
 		wall_side.MaxEdge = readV3F1000(is);
 	}
+	else if (type == NODEBOX_CONNECTED)
+	{
+#define READBOXES(box) do { \
+		count = readU16(is); \
+		(box).reserve(count); \
+		while (count--) { \
+			v3f min = readV3F1000(is); \
+			v3f max = readV3F1000(is); \
+			(box).push_back(aabb3f(min, max)); }; } while (0)
+
+		u16 count;
+
+		READBOXES(fixed);
+		READBOXES(connect_top);
+		READBOXES(connect_bottom);
+		READBOXES(connect_front);
+		READBOXES(connect_left);
+		READBOXES(connect_back);
+		READBOXES(connect_right);
+	}
 }
 
 /*
@@ -261,6 +329,8 @@ void ContentFeatures::reset()
 	sound_footstep = SimpleSoundSpec();
 	sound_dig = SimpleSoundSpec("__group");
 	sound_dug = SimpleSoundSpec();
+	connects_to.clear();
+	connects_to_ids.clear();
 }
 
 void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
@@ -328,6 +398,10 @@ void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 	os<<serializeString(mesh);
 	collision_box.serialize(os, protocol_version);
 	writeU8(os, floodable);
+	writeU16(os, connects_to_ids.size());
+	for (std::set<content_t>::const_iterator i = connects_to_ids.begin();
+			i != connects_to_ids.end(); ++i)
+		writeU16(os, *i);
 }
 
 void ContentFeatures::deSerialize(std::istream &is)
@@ -402,6 +476,9 @@ void ContentFeatures::deSerialize(std::istream &is)
 	mesh = deSerializeString(is);
 	collision_box.deSerialize(is);
 	floodable = readU8(is);
+	u16 connects_to_size = readU16(is);
+	for (u16 i = 0; i < connects_to_size; i++)
+		connects_to_ids.insert(readU16(is));
 	}catch(SerializationError &e) {};
 }
 
@@ -439,6 +516,8 @@ public:
 	virtual bool cancelNodeResolveCallback(NodeResolver *nr);
 	virtual void runNodeResolveCallbacks();
 	virtual void resetNodeResolveState();
+	virtual void mapNodeboxConnections();
+	virtual bool nodeboxConnects(MapNode from, MapNode to);
 
 private:
 	void addNameIdMapping(content_t i, std::string name);
@@ -1438,6 +1517,39 @@ void CNodeDefManager::resetNodeResolveState()
 	m_pending_resolve_callbacks.clear();
 }
 
+void CNodeDefManager::mapNodeboxConnections()
+{
+	for (u32 i = 0; i < m_content_features.size(); i++) {
+		ContentFeatures *f = &m_content_features[i];
+		if ((f->drawtype != NDT_NODEBOX) || (f->node_box.type != NODEBOX_CONNECTED))
+			continue;
+		for (std::vector<std::string>::iterator it = f->connects_to.begin();
+				it != f->connects_to.end(); ++it) {
+			getIds(*it, f->connects_to_ids);
+		}
+	}
+}
+
+bool CNodeDefManager::nodeboxConnects(MapNode from, MapNode to)
+{
+	const ContentFeatures &f1 = get(from);
+
+	if ((f1.drawtype != NDT_NODEBOX) || (f1.node_box.type != NODEBOX_CONNECTED))
+		return false;
+
+	// lookup target in connected set
+	if (f1.connects_to_ids.find(to.param0) == f1.connects_to_ids.end())
+		return false;
+
+	const ContentFeatures &f2 = get(to);
+
+	if ((f2.drawtype == NDT_NODEBOX) && (f1.node_box.type == NODEBOX_CONNECTED))
+		// ignores actually looking if back connection exists
+		return (f2.connects_to_ids.find(from.param0) != f2.connects_to_ids.end());
+
+	// the target is just a regular node, so connect no matter back connection
+	return true;
+}
 
 ////
 //// NodeResolver
diff --git a/src/nodedef.h b/src/nodedef.h
index bf2c7bc72..f92a3a941 100644
--- a/src/nodedef.h
+++ b/src/nodedef.h
@@ -80,6 +80,7 @@ enum NodeBoxType
 	NODEBOX_FIXED, // Static separately defined box(es)
 	NODEBOX_WALLMOUNTED, // Box for wall mounted nodes; (top, bottom, side)
 	NODEBOX_LEVELED, // Same as fixed, but with dynamic height from param2. for snow, ...
+	NODEBOX_CONNECTED, // optionally draws nodeboxes if a neighbor node attaches
 };
 
 struct NodeBox
@@ -92,6 +93,13 @@ struct NodeBox
 	aabb3f wall_top;
 	aabb3f wall_bottom;
 	aabb3f wall_side; // being at the -X side
+	// NODEBOX_CONNECTED
+	std::vector<aabb3f> connect_top;
+	std::vector<aabb3f> connect_bottom;
+	std::vector<aabb3f> connect_front;
+	std::vector<aabb3f> connect_left;
+	std::vector<aabb3f> connect_back;
+	std::vector<aabb3f> connect_right;
 
 	NodeBox()
 	{ reset(); }
@@ -269,6 +277,9 @@ struct ContentFeatures
 	SimpleSoundSpec sound_dig;
 	SimpleSoundSpec sound_dug;
 
+	std::vector<std::string> connects_to;
+	std::set<content_t> connects_to_ids;
+
 	/*
 		Methods
 	*/
@@ -314,6 +325,7 @@ public:
 
 	virtual void pendNodeResolve(NodeResolver *nr)=0;
 	virtual bool cancelNodeResolveCallback(NodeResolver *nr)=0;
+	virtual bool nodeboxConnects(const MapNode from, const MapNode to)=0;
 };
 
 class IWritableNodeDefManager : public INodeDefManager {
@@ -368,6 +380,7 @@ public:
 	virtual bool cancelNodeResolveCallback(NodeResolver *nr)=0;
 	virtual void runNodeResolveCallbacks()=0;
 	virtual void resetNodeResolveState()=0;
+	virtual void mapNodeboxConnections()=0;
 };
 
 IWritableNodeDefManager *createNodeDefManager();
diff --git a/src/script/common/c_content.cpp b/src/script/common/c_content.cpp
index 96fb78d99..ababf0718 100644
--- a/src/script/common/c_content.cpp
+++ b/src/script/common/c_content.cpp
@@ -535,6 +535,18 @@ ContentFeatures read_content_features(lua_State *L, int index)
 		f.node_box = read_nodebox(L, -1);
 	lua_pop(L, 1);
 
+	lua_getfield(L, index, "connects_to");
+	if (lua_istable(L, -1)) {
+		int table = lua_gettop(L);
+		lua_pushnil(L);
+		while (lua_next(L, table) != 0) {
+			// Value at -1
+			f.connects_to.push_back(lua_tostring(L, -1));
+			lua_pop(L, 1);
+		}
+	}
+	lua_pop(L, 1);
+
 	lua_getfield(L, index, "selection_box");
 	if(lua_istable(L, -1))
 		f.selection_box = read_nodebox(L, -1);
@@ -627,25 +639,31 @@ NodeBox read_nodebox(lua_State *L, int index)
 		nodebox.type = (NodeBoxType)getenumfield(L, index, "type",
 				ScriptApiNode::es_NodeBoxType, NODEBOX_REGULAR);
 
-		lua_getfield(L, index, "fixed");
-		if(lua_istable(L, -1))
-			nodebox.fixed = read_aabb3f_vector(L, -1, BS);
-		lua_pop(L, 1);
-
-		lua_getfield(L, index, "wall_top");
-		if(lua_istable(L, -1))
-			nodebox.wall_top = read_aabb3f(L, -1, BS);
-		lua_pop(L, 1);
-
-		lua_getfield(L, index, "wall_bottom");
-		if(lua_istable(L, -1))
-			nodebox.wall_bottom = read_aabb3f(L, -1, BS);
-		lua_pop(L, 1);
-
-		lua_getfield(L, index, "wall_side");
-		if(lua_istable(L, -1))
-			nodebox.wall_side = read_aabb3f(L, -1, BS);
-		lua_pop(L, 1);
+#define NODEBOXREAD(n, s) \
+	do { \
+		lua_getfield(L, index, (s)); \
+		if (lua_istable(L, -1)) \
+			(n) = read_aabb3f(L, -1, BS); \
+		lua_pop(L, 1); \
+	} while (0)
+
+#define NODEBOXREADVEC(n, s) \
+	do { \
+		lua_getfield(L, index, (s)); \
+		if (lua_istable(L, -1)) \
+			(n) = read_aabb3f_vector(L, -1, BS); \
+		lua_pop(L, 1); \
+	} while (0)
+		NODEBOXREADVEC(nodebox.fixed, "fixed");
+		NODEBOXREAD(nodebox.wall_top, "wall_top");
+		NODEBOXREAD(nodebox.wall_bottom, "wall_bottom");
+		NODEBOXREAD(nodebox.wall_side, "wall_side");
+		NODEBOXREADVEC(nodebox.connect_top, "connect_top");
+		NODEBOXREADVEC(nodebox.connect_bottom, "connect_bottom");
+		NODEBOXREADVEC(nodebox.connect_front, "connect_front");
+		NODEBOXREADVEC(nodebox.connect_left, "connect_left");
+		NODEBOXREADVEC(nodebox.connect_back, "connect_back");
+		NODEBOXREADVEC(nodebox.connect_right, "connect_right");
 	}
 	return nodebox;
 }
diff --git a/src/script/cpp_api/s_node.cpp b/src/script/cpp_api/s_node.cpp
index a905f843d..17f0f0dac 100644
--- a/src/script/cpp_api/s_node.cpp
+++ b/src/script/cpp_api/s_node.cpp
@@ -82,6 +82,7 @@ struct EnumString ScriptApiNode::es_NodeBoxType[] =
 		{NODEBOX_FIXED, "fixed"},
 		{NODEBOX_WALLMOUNTED, "wallmounted"},
 		{NODEBOX_LEVELED, "leveled"},
+		{NODEBOX_CONNECTED, "connected"},
 		{0, NULL},
 	};
 
diff --git a/src/server.cpp b/src/server.cpp
index 2fa8c4cf8..6c008a2a1 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -320,6 +320,9 @@ Server::Server(
 	// Perform pending node name resolutions
 	m_nodedef->runNodeResolveCallbacks();
 
+	// unmap node names for connected nodeboxes
+	m_nodedef->mapNodeboxConnections();
+
 	// init the recipe hashes to speed up crafting
 	m_craftdef->initHashes(this);