Simple decorations: Make 'place_offset_y' usable with simple decorations

Necessary for placing the base cube of 'plantlike_rooted' drawtype in the
seabed instead of on it.
Useful for placing decorations sunk into, or buried in, the ground.

3 files changed, 16 insertions, 11 deletions

diff --git a/src/mg_decoration.cpp b/src/mg_decoration.cpp
index cb4705177..ada37bab4 100644
--- a/src/mg_decoration.cpp
+++ b/src/mg_decoration.cpp
@@ -219,6 +219,10 @@ size_t DecoSimple::generate(MMVManip *vm, PcgRandom *pr, v3s16 p)
 	if (c_decos.empty())
 		return 0;
 
+	// Check for a negative place_offset_y causing placement below the voxelmanip
+	if (p.Y + 1 + place_offset_y < vm->m_area.MinEdge.Y)
+		return 0;
+
 	if (!canPlaceDecoration(vm, p))
 		return 0;
 
@@ -234,9 +238,10 @@ size_t DecoSimple::generate(MMVManip *vm, PcgRandom *pr, v3s16 p)
 
 	const v3s16 &em = vm->m_area.getExtent();
 	u32 vi = vm->m_area.index(p);
+	vm->m_area.add_y(em, vi, place_offset_y);
+
 	for (int i = 0; i < height; i++) {
 		vm->m_area.add_y(em, vi, 1);
-
 		content_t c = vm->m_data[vi].getContent();
 		if (c != CONTENT_AIR && c != CONTENT_IGNORE &&
 				!force_placement)
@@ -251,7 +256,8 @@ size_t DecoSimple::generate(MMVManip *vm, PcgRandom *pr, v3s16 p)
 
 int DecoSimple::getHeight()
 {
-	return (deco_height_max > 0) ? deco_height_max : deco_height;
+	return ((deco_height_max > 0) ? deco_height_max : deco_height)
+		+ place_offset_y;
 }
 
 
diff --git a/src/mg_decoration.h b/src/mg_decoration.h
index b63e62eff..9295d1a20 100644
--- a/src/mg_decoration.h
+++ b/src/mg_decoration.h
@@ -69,6 +69,7 @@ public:
 	NoiseParams np;
 	std::vector<content_t> c_spawnby;
 	s16 nspawnby;
+	s16 place_offset_y = 0;
 
 	std::unordered_set<u8> biomes;
 };
@@ -96,7 +97,6 @@ public:
 	virtual int getHeight();
 
 	Rotation rotation;
-	s16 place_offset_y = 0;
 	Schematic *schematic = nullptr;
 };
 
diff --git a/src/script/lua_api/l_mapgen.cpp b/src/script/lua_api/l_mapgen.cpp
index f475a8f7f..9ec4d5002 100644
--- a/src/script/lua_api/l_mapgen.cpp
+++ b/src/script/lua_api/l_mapgen.cpp
@@ -906,12 +906,13 @@ int ModApiMapgen::l_register_decoration(lua_State *L)
 		return 0;
 	}
 
-	deco->name       = getstringfield_default(L, index, "name", "");
-	deco->fill_ratio = getfloatfield_default(L, index, "fill_ratio", 0.02);
-	deco->y_min      = getintfield_default(L, index, "y_min", -31000);
-	deco->y_max      = getintfield_default(L, index, "y_max", 31000);
-	deco->nspawnby   = getintfield_default(L, index, "num_spawn_by", -1);
-	deco->sidelen    = getintfield_default(L, index, "sidelen", 8);
+	deco->name           = getstringfield_default(L, index, "name", "");
+	deco->fill_ratio     = getfloatfield_default(L, index, "fill_ratio", 0.02);
+	deco->y_min          = getintfield_default(L, index, "y_min", -31000);
+	deco->y_max          = getintfield_default(L, index, "y_max", 31000);
+	deco->nspawnby       = getintfield_default(L, index, "num_spawn_by", -1);
+	deco->place_offset_y = getintfield_default(L, index, "place_offset_y", 0);
+	deco->sidelen        = getintfield_default(L, index, "sidelen", 8);
 	if (deco->sidelen <= 0) {
 		errorstream << "register_decoration: sidelen must be "
 			"greater than 0" << std::endl;
@@ -1024,8 +1025,6 @@ bool read_deco_schematic(lua_State *L, SchematicManager *schemmgr, DecoSchematic
 	deco->rotation = (Rotation)getenumfield(L, index, "rotation",
 		ModApiMapgen::es_Rotation, ROTATE_0);
 
-	deco->place_offset_y = getintfield_default(L, index, "place_offset_y", 0);
-
 	StringMap replace_names;
 	lua_getfield(L, index, "replacements");
 	if (lua_istable(L, -1))