Mgv6 mudflow: Avoid partially removed stacked decorations

Recently we started to remove decorations if the dirt below was flowed away,
but this did not check for stacked decorations, causing them to have only
their lowest node removed.
Also, placed mud could partially bury stacked decorations.

Remove 'old_is_water' bool which on testing is never true.
Add new function 'moveMud()' to reduce indentation.
Remove stacked decoration nodes above a removed decoration.
Remove stacked decorations partially buried in placed mud.

2 files changed, 41 insertions, 19 deletions

diff --git a/src/mapgen_v6.cpp b/src/mapgen_v6.cpp
index f84f3b548..7bf2ea9db 100644
--- a/src/mapgen_v6.cpp
+++ b/src/mapgen_v6.cpp
@@ -884,26 +884,11 @@ void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
 					} while (ndef->get(*n2).walkable == false);
 					// Loop one up so that we're in air
 					vm->m_area.add_y(em, i2, 1);
-					n2 = &vm->m_data[i2];
 
-					bool old_is_water = (n->getContent() == c_water_source);
-					// Move mud to new place
-					if (!dropped_to_unknown) {
-						*n2 = *n;
-						// Set old place to be air (or water)
-						if (old_is_water) {
-							*n = MapNode(c_water_source);
-						} else {
-							*n = MapNode(CONTENT_AIR);
-							// Upper (n3) is not walkable or is NULL. If it is
-							// not NULL and not air and not water it is a
-							// decoration that needs removing, to avoid
-							// unsupported decorations.
-							if (n3 && n3->getContent() != CONTENT_AIR &&
-									n3->getContent() != c_water_source)
-								*n3 = MapNode(CONTENT_AIR);
-						}
-					}
+					// Move mud to new place. Outside mapchunk remove
+					// any decorations above removed or placed mud.
+					if (!dropped_to_unknown)
+						moveMud(i, i2, i3, p2d, em);
 
 					// Done
 					break;
@@ -915,6 +900,41 @@ void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
 }
 
 
+void MapgenV6::moveMud(u32 remove_index, u32 place_index,
+	u32 above_remove_index, v2s16 pos, v3s16 em)
+{
+	MapNode n_air(CONTENT_AIR);
+	// Copy mud from old place to new place
+	vm->m_data[place_index] = vm->m_data[remove_index];
+	// Set old place to be air
+	vm->m_data[remove_index] = n_air;
+	// Outside the mapchunk decorations may need to be removed if above removed
+	// mud or if half-buried in placed mud. Placed mud is to the side of pos so
+	// use 'pos.X >= node_max.X' etc.
+	if (pos.X >= node_max.X || pos.X <= node_min.X ||
+			pos.Y >= node_max.Z || pos.Y <= node_min.Z) {
+		// 'above remove' node is above removed mud. If it is not air and not
+		// water it is a decoration that needs removing. Also search upwards
+		// for a possible stacked decoration.
+		while (vm->m_area.contains(above_remove_index) &&
+				vm->m_data[above_remove_index].getContent() != CONTENT_AIR &&
+				vm->m_data[above_remove_index].getContent() != c_water_source) {
+			vm->m_data[above_remove_index] = n_air;
+			vm->m_area.add_y(em, above_remove_index, 1);
+		}
+		// Mud placed may have half-buried a tall decoration, search above and
+		// remove.
+		vm->m_area.add_y(em, place_index, 1);
+		while (vm->m_area.contains(place_index) &&
+				vm->m_data[place_index].getContent() != CONTENT_AIR &&
+				vm->m_data[place_index].getContent() != c_water_source) {
+			vm->m_data[place_index] = n_air;
+			vm->m_area.add_y(em, place_index, 1);
+		}
+	}
+}
+
+
 void MapgenV6::placeTreesAndJungleGrass()
 {
 	//TimeTaker t("placeTrees");
diff --git a/src/mapgen_v6.h b/src/mapgen_v6.h
index 2b3b4444e..9d36804d0 100644
--- a/src/mapgen_v6.h
+++ b/src/mapgen_v6.h
@@ -162,6 +162,8 @@ public:
 	int generateGround();
 	void addMud();
 	void flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos);
+	void moveMud(u32 remove_index, u32 place_index,
+		u32 above_remove_index, v2s16 pos, v3s16 em);
 	void growGrass();
 	void placeTreesAndJungleGrass();
 	virtual void generateCaves(int max_stone_y);