Cavegen: Place correct biome surface in tunnel entrances

Previously in tunnel entrance floors only a single biome 'top' node was
placed and 'filler' nodes were missing.

Place 'top' and 'filler' nodes in tunnel entrance floors with depths
defined by the biome.
In tunnel entrances under rivers 'riverbed' nodes are placed to the
biome-defined depth.

1 files changed, 33 insertions, 15 deletions

diff --git a/src/cavegen.cpp b/src/cavegen.cpp
index bb6aa25a6..1005640c1 100644
--- a/src/cavegen.cpp
+++ b/src/cavegen.cpp
@@ -74,19 +74,23 @@ void CavesNoiseIntersection::generateCaves(MMVManip *vm,
 	noise_cave2->perlinMap3D(nmin.X, nmin.Y - 1, nmin.Z);
 
 	v3s16 em = vm->m_area.getExtent();
-	u32 index2d = 0;
+	u32 index2d = 0;  // Biomemap index
 
 	for (s16 z = nmin.Z; z <= nmax.Z; z++)
 	for (s16 x = nmin.X; x <= nmax.X; x++, index2d++) {
 		bool column_is_open = false;  // Is column open to overground
 		bool is_under_river = false;  // Is column under river water
-		bool is_tunnel = false;  // Is tunnel or tunnel floor
+		bool is_under_tunnel = false;  // Is tunnel or is under tunnel
+		// Indexes at column top
 		u32 vi = vm->m_area.index(x, nmax.Y, z);
 		u32 index3d = (z - nmin.Z) * m_zstride_1d + m_csize.Y * m_ystride +
-			(x - nmin.X);
+			(x - nmin.X);  // 3D noise index
 		// Biome of column
 		Biome *biome = (Biome *)m_bmgr->getRaw(biomemap[index2d]);
-
+		u16 depth_top = biome->depth_top;
+		u16 base_filler = depth_top + biome->depth_filler;
+		u16 depth_riverbed = biome->depth_riverbed;
+		u16 nplaced = 0;
 		// Don't excavate the overgenerated stone at nmax.Y + 1,
 		// this creates a 'roof' over the tunnel, preventing light in
 		// tunnels at mapchunk borders when generating mapchunks upwards.
@@ -112,20 +116,34 @@ void CavesNoiseIntersection::generateCaves(MMVManip *vm,
 			if (d1 * d2 > m_cave_width && m_ndef->get(c).is_ground_content) {
 				// In tunnel and ground content, excavate
 				vm->m_data[vi] = MapNode(CONTENT_AIR);
-				is_tunnel = true;
-			} else {
-				// Not in tunnel or not ground content
-				if (is_tunnel && column_is_open &&
-						(c == biome->c_filler || c == biome->c_stone)) {
-					// Tunnel entrance floor
-					if (is_under_river)
+				is_under_tunnel = true;
+			} else if (column_is_open && is_under_tunnel &&
+					(c == biome->c_stone || c == biome->c_filler)) {
+				// Tunnel entrance floor, place biome surface nodes
+				if (is_under_river) {
+					if (nplaced < depth_riverbed) {
 						vm->m_data[vi] = MapNode(biome->c_riverbed);
-					else
-						vm->m_data[vi] = MapNode(biome->c_top);
+						nplaced++;
+					} else {
+						// Disable top/filler placement
+						column_is_open = false;
+						is_under_river = false;
+						is_under_tunnel = false;
+					}
+				} else if (nplaced < depth_top) {
+					vm->m_data[vi] = MapNode(biome->c_top);
+					nplaced++;
+				} else if (nplaced < base_filler) {
+					vm->m_data[vi] = MapNode(biome->c_filler);
+					nplaced++;
+				} else {
+					// Disable top/filler placement
+					column_is_open = false;
+					is_under_tunnel = false;
 				}
-
+			} else {
+				// Not tunnel or tunnel entrance floor
 				column_is_open = false;
-				is_tunnel = false;
 			}
 		}
 	}