* refactored liquid transformation code (has some flaws)

Completely rewrote the liquid transformation. The algorithm now exclusively modifies the current node in one iteration. Another change is that MapNode.param2 now stores a bit that tells other nodes if a flowing liquid node flows downwards. This is accomplished by two masks on param2 for the "flow down" bit and the "liquid level" bits.

This will be the base of future improvements to the liquid flow. However, in the current state flowing liquid does not always disappear when cut off its source. Be aware that this branch is work in progress.

3 files changed, 208 insertions, 252 deletions

diff --git a/src/content_mapblock.cpp b/src/content_mapblock.cpp
index 4c28fe3c6..d8bf71dc0 100644
--- a/src/content_mapblock.cpp
+++ b/src/content_mapblock.cpp
@@ -375,7 +375,7 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 					if(n2.d == CONTENT_WATERSOURCE)
 						level = (-0.5+node_water_level) * BS;
 					else if(n2.d == CONTENT_WATER)
-						level = (-0.5 + ((float)n2.param2 + 0.5) / 8.0
+						level = (-0.5 + ((float)(n2.param2 & LIQUID_LEVEL_MASK) + 0.5) / 8.0
 								* node_water_level) * BS;
 
 					// Check node above neighbor.
diff --git a/src/map.cpp b/src/map.cpp
index 10e1302b1..298826e7e 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -1086,7 +1086,7 @@ void Map::addNodeAndUpdate(v3s16 p, MapNode n,
 		v3s16 p2 = p + dirs[i];
 
 		MapNode n2 = getNode(p2);
-		if(content_liquid(n2.d))
+		if(content_liquid(n2.d) || n2.d == CONTENT_AIR)
 		{
 			m_transforming_liquid.push_back(p2);
 		}
@@ -1241,18 +1241,10 @@ void Map::removeNodeAndUpdate(v3s16 p,
 
 	/*
 		Add neighboring liquid nodes to transform queue.
-
-		Also add horizontal neighbors of node on top of removed node
-		because they could be affected of the water on top flowing
-		down instead of into them.
 	*/
 	v3s16 dirs[10] = {
 		v3s16(0,0,1), // back
 		v3s16(0,1,0), // top
-		v3s16(1,1,0), // topright
-		v3s16(-1,1,0), // topleft
-		v3s16(0,1,1), // topback
-		v3s16(0,1,-1), // topfront
 		v3s16(1,0,0), // right
 		v3s16(0,0,-1), // front
 		v3s16(0,-1,0), // bottom
@@ -1266,7 +1258,7 @@ void Map::removeNodeAndUpdate(v3s16 p,
 		v3s16 p2 = p + dirs[i];
 
 		MapNode n2 = getNode(p2);
-		if(content_liquid(n2.d))
+		if(content_liquid(n2.d) || n2.d == CONTENT_AIR)
 		{
 			m_transforming_liquid.push_back(p2);
 		}
@@ -1546,6 +1538,17 @@ void Map::PrintInfo(std::ostream &out)
 
 #define WATER_DROP_BOOST 4
 
+enum NeighborType {
+	NEIGHBOR_UPPER,
+	NEIGHBOR_SAME_LEVEL,
+	NEIGHBOR_LOWER
+};
+struct NodeNeighbor {
+	MapNode n;
+	NeighborType t;
+	v3s16 p;
+};
+
 void Map::transformLiquids(core::map<v3s16, MapBlock*> & modified_blocks)
 {
 	DSTACK(__FUNCTION_NAME);
@@ -1565,264 +1568,210 @@ void Map::transformLiquids(core::map<v3s16, MapBlock*> & modified_blocks)
 		v3s16 p0 = m_transforming_liquid.pop_front();
 
 		MapNode n0 = getNodeNoEx(p0);
-
-		// Don't deal with non-liquids
-		if(content_liquid(n0.d) == false)
-			continue;
-
-		bool is_source = !content_flowing_liquid(n0.d);
-
-		u8 liquid_level = 8;
-		if(is_source == false)
-			liquid_level = n0.param2 & 0x0f;
-
-		// Turn possible source into non-source
-		u8 nonsource_c = make_liquid_flowing(n0.d);
-
-		// Counts surrounding liquid source blocks
-		u8 surrounding_sources = 0;
-
+				
 		/*
-			If not source, check that some node flows into this one
-			and what is the level of liquid in this one
-		*/
-		if(is_source == false)
-		{
-			s8 new_liquid_level_max = -1;
-
-			v3s16 dirs_from[5] = {
-				v3s16(0,1,0), // top
-				v3s16(0,0,1), // back
-				v3s16(1,0,0), // right
-				v3s16(0,0,-1), // front
-				v3s16(-1,0,0), // left
-			};
-			for(u16 i=0; i<5; i++)
-			{
-				bool from_top = (i==0);
-
-				v3s16 p2 = p0 + dirs_from[i];
-				MapNode n2 = getNodeNoEx(p2);
-
-				if(content_liquid(n2.d))
-				{
-					u8 n2_nonsource_c = make_liquid_flowing(n2.d);
-					// Check that the liquids are the same type
-					if(n2_nonsource_c != nonsource_c)
-					{
-						dstream<<"WARNING: Not handling: different liquids"
-								" collide"<<std::endl;
-						continue;
+			Collect information about current node
+		 */
+		s8 liquid_level = -1;
+		u8 liquid_kind;
+		LiquidType liquid_type = content_features(n0.d).liquid_type;
+		switch (liquid_type) {
+			case LIQUID_SOURCE:
+				liquid_level = 8;
+				liquid_kind = content_features(n0.d).liquid_alternative_flowing;
+				break;
+			case LIQUID_FLOWING:
+				liquid_level = (n0.param2 & LIQUID_LEVEL_MASK);
+				liquid_kind = n0.d;
+				break;
+			case LIQUID_NONE:
+				// if this is an air node, it *could* be transformed into a liquid. otherwise,
+				// continue with the next node.
+				if (n0.d != CONTENT_AIR)
+					continue;
+				liquid_kind = CONTENT_AIR;
+				break;
+		}
+		
+		/*
+			Collect information about the environment
+		 */
+		v3s16 dirs[6] = {
+			v3s16( 0, 1, 0), // top
+			v3s16( 0,-1, 0), // bottom
+			v3s16( 1, 0, 0), // right
+			v3s16(-1, 0, 0), // left
+			v3s16( 0, 0, 1), // back
+			v3s16( 0, 0,-1)  // front
+		};
+		NodeNeighbor sources[6]; // surrounding sources
+		int num_sources = 0;
+		NodeNeighbor flows[6]; // surrounding flowing liquid nodes
+		int num_flows = 0;
+		NodeNeighbor airs[6]; // surrounding air
+		int num_airs = 0;
+		NodeNeighbor neutrals[6]; // nodes that are solid, another kind of liquid
+		int num_neutrals = 0;
+		bool flowing_down = false;
+		for (u16 i = 0; i < 6; i++) {
+			NeighborType nt = NEIGHBOR_SAME_LEVEL;
+			switch (i) {
+				case 0:
+					nt = NEIGHBOR_UPPER;
+					break;
+				case 1:
+					nt = NEIGHBOR_LOWER;
+					break;
+			}
+			v3s16 npos = p0 + dirs[i];
+			NodeNeighbor nb = {getNodeNoEx(npos), nt, npos};
+			switch (content_features(nb.n.d).liquid_type) {
+				case LIQUID_NONE:
+					if (nb.n.d == CONTENT_AIR) {
+						airs[num_airs++] = nb;
+						// if the current nodes happens to be a flowing node, it will start to flow down here.
+						if (nb.t == NEIGHBOR_LOWER)
+							flowing_down = true;
+					} else {
+						neutrals[num_neutrals++] = nb;
 					}
-					bool n2_is_source = !content_flowing_liquid(n2.d);
-					s8 n2_liquid_level = 8;
-					if(n2_is_source)
-						surrounding_sources++;
-					else
-						n2_liquid_level = n2.param2 & 0x07;
-
-					s8 new_liquid_level = -1;
-					if(from_top)
-					{
-						//new_liquid_level = 7;
-						if(n2_liquid_level >= 7 - WATER_DROP_BOOST)
-							new_liquid_level = 7;
-						else
-							new_liquid_level = n2_liquid_level + WATER_DROP_BOOST;
+					break;
+				case LIQUID_SOURCE:
+					// if this node is not (yet) of a liquid type, choose the first liquid type we encounter 
+					if (liquid_kind == CONTENT_AIR)
+						liquid_kind = content_features(nb.n.d).liquid_alternative_flowing;
+					if (content_features(nb.n.d).liquid_alternative_flowing !=liquid_kind) {
+						neutrals[num_neutrals++] = nb;
+					} else {
+						sources[num_sources++] = nb;
 					}
-					else if(n2_liquid_level > 0)
-					{
-						// If the neighbor node isn't a source and flows downwards,
-						// it doesn't flow into this node
-						if (n2_is_source)
-						{
-							new_liquid_level = n2_liquid_level - 1;
-						}
-						else
-						{
-							// Node below n2
-							MapNode n3 = getNodeNoEx(p2 + v3s16(0,-1,0));
-							// NOTE: collision of different liquids not yet handled here.
-							if (content_features(n3.d).liquid_type != LIQUID_FLOWING)
-							new_liquid_level = n2_liquid_level - 1;
+					break;
+				case LIQUID_FLOWING:
+					// if this node is not (yet) of a liquid type, choose the first liquid type we encounter
+					// (while ignoring flowing liquids at the lowest level, which cannot flow into this node)
+					if (liquid_kind == CONTENT_AIR && ((nb.n.param2 & LIQUID_LEVEL_MASK) > 0))
+						liquid_kind = content_features(nb.n.d).liquid_alternative_flowing;
+					if (content_features(nb.n.d).liquid_alternative_flowing != liquid_kind) {
+						neutrals[num_neutrals++] = nb;
+					} else {
+						// order flowing neighbors by liquid level descending
+						int	insert_at = 0;
+						while (insert_at < num_flows && ((flows[insert_at].n.param2 & LIQUID_LEVEL_MASK) >
+														 (nb.n.param2 & LIQUID_LEVEL_MASK))) {
+							insert_at++;
 						}
+						flows[insert_at] = nb;
+						num_flows++;
+						if (nb.t == NEIGHBOR_LOWER)
+							flowing_down = true;
 					}
-
-					if(new_liquid_level > new_liquid_level_max)
-						new_liquid_level_max = new_liquid_level;
-				}
-			} //for
-
-			/*
-				If liquid level should be something else, update it and
-				add all the neighboring water nodes to the transform queue.
-			*/
-			if(new_liquid_level_max != liquid_level || (!is_source && surrounding_sources >= 2))
-			{
-				if (surrounding_sources >= 2)
-				{
-					n0.d = content_features(n0.d).liquid_alternative_source;
-					setNode(p0,n0);
-				}
-				else if(new_liquid_level_max == -1)
-				{
-					// Remove water alltoghether
-					n0.d = CONTENT_AIR;
-					n0.param2 = 0;
-					setNode(p0, n0);
-				}
-				else
-				{
-					n0.param2 = new_liquid_level_max;
-					liquid_level = new_liquid_level_max;
-					setNode(p0, n0);
-				}
-
-				// Block has been modified
-				{
-					v3s16 blockpos = getNodeBlockPos(p0);
-					MapBlock *block = getBlockNoCreateNoEx(blockpos);
-					if(block != NULL)
-						modified_blocks.insert(blockpos, block);
-				}
-
-				/*
-					Add neighboring non-source liquid nodes to transform queue.
-				*/
-				v3s16 dirs[6] = {
-					v3s16(0,0,1), // back
-					v3s16(0,1,0), // top
-					v3s16(1,0,0), // right
-					v3s16(0,0,-1), // front
-					v3s16(0,-1,0), // bottom
-					v3s16(-1,0,0), // left
-				};
-				for(u16 i=0; i<6; i++)
-				{
-					v3s16 p2 = p0 + dirs[i];
-
-					MapNode n2 = getNodeNoEx(p2);
-					if(content_flowing_liquid(n2.d))
-					{
-						m_transforming_liquid.push_back(p2);
-					}
-				}
+					break;
 			}
 		}
-
-		// Get a new one from queue if the node has turned into non-water
-		if(content_liquid(n0.d) == false)
-			continue;
-
+		
 		/*
-			Flow water from this node
-		*/
-		v3s16 dirs_to[5] = {
-			v3s16(0,-1,0), // bottom
-			v3s16(0,0,1), // back
-			v3s16(1,0,0), // right
-			v3s16(0,0,-1), // front
-			v3s16(-1,0,0), // left
-		};
-		for(u16 i=0; i<5; i++)
-		{
-			bool to_bottom = (i == 0);
-
-			// If liquid is at lowest possible height, it's not going
-			// anywhere except down
-			if(liquid_level == 0 && to_bottom == false)
-				continue;
-
-			u8 liquid_next_level = 0;
-			// If going to bottom
-			if(to_bottom)
-			{
-				//liquid_next_level = 7;
-				if(liquid_level >= 7 - WATER_DROP_BOOST)
-					liquid_next_level = 7;
-				else
-					liquid_next_level = liquid_level + WATER_DROP_BOOST;
+			decide on the type (and possibly level) of the current node
+		 */
+		u8 new_node_content;
+		s8 new_node_level = -1;
+		if (num_sources >= 2 || liquid_type == LIQUID_SOURCE) {
+			// liquid_kind will be set to either the flowing alternative of the node (if it's a liquid)
+			// or the flowing alternative of the first of the surrounding sources (if it's air), so
+			// it's perfectly safe to use liquid_kind here to determine the new node content.
+			new_node_content = content_features(liquid_kind).liquid_alternative_source;
+		} else if (num_sources == 1 && sources[0].t != NEIGHBOR_LOWER) {
+			// liquid_kind is set properly, see above
+			new_node_content = liquid_kind;
+			new_node_level = 7;
+		} else {
+			// no surrounding sources, so get the maximum level that can flow into this node
+			for (u16 i = 0; i < num_flows; i++) {
+				u8 nb_liquid_level = (flows[i].n.param2 & LIQUID_LEVEL_MASK);
+				switch (flows[i].t) {
+					case NEIGHBOR_UPPER:
+						if (nb_liquid_level + WATER_DROP_BOOST > new_node_level) {
+							new_node_level = 7;
+							if (nb_liquid_level + WATER_DROP_BOOST < 7)
+								new_node_level = nb_liquid_level + WATER_DROP_BOOST;
+						}
+						break;
+					case NEIGHBOR_LOWER:
+						break;
+					case NEIGHBOR_SAME_LEVEL:
+						if ((flows[i].n.param2 & LIQUID_FLOW_DOWN_MASK) != LIQUID_FLOW_DOWN_MASK &&
+							nb_liquid_level > 0 && nb_liquid_level - 1 > new_node_level) {
+							new_node_level = nb_liquid_level - 1;
+						}
+						break;
+				}
 			}
+			if (new_node_level >= 0)
+				new_node_content = liquid_kind;
 			else
-				liquid_next_level = liquid_level - 1;
-
-			bool n2_changed = false;
-			bool flowed = false;
-
-			v3s16 p2 = p0 + dirs_to[i];
-
-			MapNode n2 = getNodeNoEx(p2);
-			//dstream<<"[1] n2.param="<<(int)n2.param<<std::endl;
-
-			if(content_liquid(n2.d))
-			{
-				u8 n2_nonsource_c = make_liquid_flowing(n2.d);
-				// Check that the liquids are the same type
-				if(n2_nonsource_c != nonsource_c)
-				{
-					dstream<<"WARNING: Not handling: different liquids"
-							" collide"<<std::endl;
-					continue;
-				}
-				bool n2_is_source = !content_flowing_liquid(n2.d);
-				u8 n2_liquid_level = 8;
-				if(n2_is_source == false)
-					n2_liquid_level = n2.param2 & 0x07;
-
-				if(to_bottom)
-				{
-					flowed = true;
-				}
-
-				if(n2_is_source)
-				{
-					// Just flow into the source, nothing changes.
-					// n2_changed is not set because destination didn't change
-					flowed = true;
+				new_node_content = CONTENT_AIR;
+		}
+		
+		/*
+			check if anything has changed. if not, just continue with the next node.
+		 */
+		if (new_node_content == n0.d && (content_features(n0.d).liquid_type != LIQUID_FLOWING ||
+										 ((n0.param2 & LIQUID_LEVEL_MASK) == (u8)new_node_level) &&
+										 ((n0.param2 & LIQUID_FLOW_DOWN_MASK) == LIQUID_FLOW_DOWN_MASK)
+										 == flowing_down))
+			continue;
+		
+		/*
+			update the current node
+		 */
+		bool flow_down_enabled = (flowing_down && ((n0.param2 & LIQUID_FLOW_DOWN_MASK) != LIQUID_FLOW_DOWN_MASK));
+		n0.d = new_node_content;
+		if (content_features(n0.d).liquid_type == LIQUID_FLOWING) {
+			// set level to last 3 bits, flowing down bit to 4th bit
+			n0.param2 = (flowing_down ? LIQUID_FLOW_DOWN_MASK : 0x00) | (new_node_level & LIQUID_LEVEL_MASK); 
+		} else {
+			n0.param2 = 0;
+		}
+		setNode(p0, n0);
+		v3s16 blockpos = getNodeBlockPos(p0);
+		MapBlock *block = getBlockNoCreateNoEx(blockpos);
+		if(block != NULL)
+			modified_blocks.insert(blockpos, block);
+		
+		switch (content_features(n0.d).liquid_type) {
+			case LIQUID_SOURCE:
+				// make sure source flows into all neighboring nodes
+				for (u16 i = 0; i < num_flows; i++)
+					if (flows[i].t != NEIGHBOR_UPPER)
+						m_transforming_liquid.push_back(flows[i].p);
+				for (u16 i = 0; i < num_airs; i++)
+					if (airs[i].t != NEIGHBOR_UPPER)
+						m_transforming_liquid.push_back(airs[i].p);
+				break;
+			case LIQUID_NONE:
+				// this flow has turned to air; neighboring flows might need to do the same
+				for (u16 i = 0; i < num_flows; i++)
+					m_transforming_liquid.push_back(flows[i].p);
+				break;
+			case LIQUID_FLOWING:
+				for (u16 i = 0; i < num_flows; i++) {
+					u8 flow_level = (flows[i].n.param2 & LIQUID_LEVEL_MASK);
+					// liquid_level is still the ORIGINAL level of this node.
+					if (flows[i].t != NEIGHBOR_UPPER && ((flow_level < liquid_level || flow_level < new_node_level) ||
+						flow_down_enabled))
+						m_transforming_liquid.push_back(flows[i].p);
 				}
-				else
-				{
-					if(liquid_next_level > n2_liquid_level)
-					{
-						n2.param2 = liquid_next_level;
-						setNode(p2, n2);
-
-						n2_changed = true;
-						flowed = true;
-					}
+				for (u16 i = 0; i < num_airs; i++) {
+					if (airs[i].t != NEIGHBOR_UPPER && (airs[i].t == NEIGHBOR_LOWER || new_node_level > 0))
+						m_transforming_liquid.push_back(airs[i].p);
 				}
-			}
-			else if(n2.d == CONTENT_AIR)
-			{
-				n2.d = nonsource_c;
-				n2.param2 = liquid_next_level;
-				setNode(p2, n2);
-
-				n2_changed = true;
-				flowed = true;
-			}
-
-			//dstream<<"[2] n2.param="<<(int)n2.param<<std::endl;
-
-			if(n2_changed)
-			{
-				m_transforming_liquid.push_back(p2);
-
-				v3s16 blockpos = getNodeBlockPos(p2);
-				MapBlock *block = getBlockNoCreateNoEx(blockpos);
-				if(block != NULL)
-					modified_blocks.insert(blockpos, block);
-			}
-
-			// If n2_changed to bottom, don't flow anywhere else
-			if(to_bottom && flowed && !is_source)
 				break;
 		}
-
+		
 		loopcount++;
 		//if(loopcount >= 100000)
-		if(loopcount >= initial_size * 1)
+		if(loopcount >= initial_size * 1) {
 			break;
+		}
 	}
 	//dstream<<"Map::transformLiquids(): loopcount="<<loopcount<<std::endl;
 }
diff --git a/src/mapnode.h b/src/mapnode.h
index 8bbd4eb79..33128049a 100644
--- a/src/mapnode.h
+++ b/src/mapnode.h
@@ -405,9 +405,16 @@ enum LightBank
 };
 
 /*
+	Masks for MapNode.param2 of flowing liquids
+ */
+#define LIQUID_LEVEL_MASK 0x07
+#define LIQUID_FLOW_DOWN_MASK 0x08
+
+/*
 	This is the stuff what the whole world consists of.
 */
 
+
 struct MapNode
 {
 	/*