Decoration API: Add flag for placement on liquid surface

Add findLiquidSurface() function to mapgen.cpp
Update lua_api.txt

4 files changed, 30 insertions, 3 deletions

diff --git a/src/mapgen.cpp b/src/mapgen.cpp
index f5046459e..8a77000fa 100644
--- a/src/mapgen.cpp
+++ b/src/mapgen.cpp
@@ -161,6 +161,26 @@ s16 Mapgen::findGroundLevel(v2s16 p2d, s16 ymin, s16 ymax)
 }
 
 
+// Returns -MAX_MAP_GENERATION_LIMIT if not found or if ground is found first
+s16 Mapgen::findLiquidSurface(v2s16 p2d, s16 ymin, s16 ymax)
+{
+	v3s16 em = vm->m_area.getExtent();
+	u32 i = vm->m_area.index(p2d.X, ymax, p2d.Y);
+	s16 y;
+
+	for (y = ymax; y >= ymin; y--) {
+		MapNode &n = vm->m_data[i];
+		if (ndef->get(n).walkable)
+			return -MAX_MAP_GENERATION_LIMIT;
+		else if (ndef->get(n).isLiquid())
+			break;
+
+		vm->m_area.add_y(em, i, -1);
+	}
+	return (y >= ymin) ? y : -MAX_MAP_GENERATION_LIMIT;
+}
+
+
 void Mapgen::updateHeightmap(v3s16 nmin, v3s16 nmax)
 {
 	if (!heightmap)
diff --git a/src/mapgen.h b/src/mapgen.h
index 4b28ec936..0561ddf98 100644
--- a/src/mapgen.h
+++ b/src/mapgen.h
@@ -166,6 +166,7 @@ public:
 	static u32 getBlockSeed2(v3s16 p, int seed);
 	s16 findGroundLevelFull(v2s16 p2d);
 	s16 findGroundLevel(v2s16 p2d, s16 ymin, s16 ymax);
+	s16 findLiquidSurface(v2s16 p2d, s16 ymin, s16 ymax);
 	void updateHeightmap(v3s16 nmin, v3s16 nmax);
 	void updateLiquid(UniqueQueue<v3s16> *trans_liquid, v3s16 nmin, v3s16 nmax);
 
diff --git a/src/mg_decoration.cpp b/src/mg_decoration.cpp
index 4f543a7dd..1e080fd6a 100644
--- a/src/mg_decoration.cpp
+++ b/src/mg_decoration.cpp
@@ -30,6 +30,7 @@ FlagDesc flagdesc_deco[] = {
 	{"place_center_y", DECO_PLACE_CENTER_Y},
 	{"place_center_z", DECO_PLACE_CENTER_Z},
 	{"force_placement", DECO_FORCE_PLACEMENT},
+	{"liquid_surface", DECO_LIQUID_SURFACE},
 	{NULL,             0}
 };
 
@@ -124,9 +125,13 @@ size_t Decoration::placeDeco(Mapgen *mg, u32 blockseed, v3s16 nmin, v3s16 nmax)
 
 			int mapindex = carea_size * (z - nmin.Z) + (x - nmin.X);
 
-			s16 y = mg->heightmap ?
-					mg->heightmap[mapindex] :
-					mg->findGroundLevel(v2s16(x, z), nmin.Y, nmax.Y);
+			s16 y = -MAX_MAP_GENERATION_LIMIT;
+			if (flags & DECO_LIQUID_SURFACE)
+				y = mg->findLiquidSurface(v2s16(x, z), nmin.Y, nmax.Y);
+			else if (mg->heightmap)
+				y = mg->heightmap[mapindex];
+			else
+				y = mg->findGroundLevel(v2s16(x, z), nmin.Y, nmax.Y);
 
 			if (y < nmin.Y || y > nmax.Y ||
 				y < y_min  || y > y_max)
diff --git a/src/mg_decoration.h b/src/mg_decoration.h
index c712ce7c8..16af02a1a 100644
--- a/src/mg_decoration.h
+++ b/src/mg_decoration.h
@@ -41,6 +41,7 @@ enum DecorationType {
 #define DECO_PLACE_CENTER_Z  0x04
 #define DECO_USE_NOISE       0x08
 #define DECO_FORCE_PLACEMENT 0x10
+#define DECO_LIQUID_SURFACE  0x20
 
 extern FlagDesc flagdesc_deco[];