Mapgen: Fix light in tunnels at mapchunk borders

Don't excavate the overgenerated stone at node_max.Y + 1,
this creates a 'roof' over the tunnel, preventing light in
tunnels at mapchunk borders when generating mapchunks upwards.

src/mapgen_flat.cpp

@@ -573,6 +573,12 @@ void MapgenFlat::generateCaves(s16 max_stone_y)
 
 		for (s16 y = node_max.Y + 1; y >= node_min.Y - 1;
 				y--, index3d -= ystride, vm->m_area.add_y(em, vi, -1)) {
+			// Don't excavate the overgenerated stone at node_max.Y + 1,
+			// this creates a 'roof' over the tunnel, preventing light in
+			// tunnels at mapchunk borders when generating mapchunks upwards.
+			if (y > node_max.Y)
+				continue;
+
 			content_t c = vm->m_data[vi].getContent();
 			if (c == CONTENT_AIR || c == biome->c_water_top ||
 					c == biome->c_water) {

src/mapgen_fractal.cpp

@@ -701,6 +701,12 @@ void MapgenFractal::generateCaves(s16 max_stone_y)
 
 		for (s16 y = node_max.Y + 1; y >= node_min.Y - 1;
 				y--, index3d -= ystride, vm->m_area.add_y(em, vi, -1)) {
+			// Don't excavate the overgenerated stone at node_max.Y + 1,
+			// this creates a 'roof' over the tunnel, preventing light in
+			// tunnels at mapchunk borders when generating mapchunks upwards.
+			if (y > node_max.Y)
+				continue;
+
 			content_t c = vm->m_data[vi].getContent();
 			if (c == CONTENT_AIR || c == biome->c_water_top ||
 					c == biome->c_water) {

src/mapgen_v5.cpp

@@ -519,6 +519,12 @@ void MapgenV5::generateCaves(int max_stone_y)
 	for (s16 y = node_min.Y - 1; y <= node_max.Y + 1; y++) {
 		u32 vi = vm->m_area.index(node_min.X, y, z);
 		for (s16 x = node_min.X; x <= node_max.X; x++, vi++, index++) {
+			// Don't excavate the overgenerated stone at node_max.Y + 1,
+			// this creates a 'roof' over the tunnel, preventing light in
+			// tunnels at mapchunk borders when generating mapchunks upwards.
+			if (y > node_max.Y)
+				continue;
+
 			float d1 = contour(noise_cave1->result[index]);
 			float d2 = contour(noise_cave2->result[index]);
 			if (d1 * d2 > 0.125f) {

src/mapgen_v7.cpp

@@ -883,6 +883,12 @@ void MapgenV7::generateCaves(s16 max_stone_y)
 
 		for (s16 y = node_max.Y + 1; y >= node_min.Y - 1;
 				y--, index3d -= ystride, vm->m_area.add_y(em, vi, -1)) {
+			// Don't excavate the overgenerated stone at node_max.Y + 1,
+			// this creates a 'roof' over the tunnel, preventing light in
+			// tunnels at mapchunk borders when generating mapchunks upwards.
+			if (y > node_max.Y)
+				continue;
+
 			content_t c = vm->m_data[vi].getContent();
 			if (c == CONTENT_AIR || c == biome->c_water_top ||
 					c == biome->c_water) {

src/mapgen_valleys.cpp

@@ -931,6 +931,12 @@ void MapgenValleys::generateCaves(s16 max_stone_y)
 		for (s16 y = node_max.Y + 1;
 				y >= node_min.Y - 1;
 				y--, index_3d -= ystride, vm->m_area.add_y(em, index_data, -1)) {
+			// Don't excavate the overgenerated stone at node_max.Y + 1,
+			// this creates a 'roof' over the tunnel, preventing light in
+			// tunnels at mapchunk borders when generating mapchunks upwards.
+			if (y > node_max.Y)
+				continue;
+
 			float terrain = noise_terrain_height->result[index_2d];
 
 			// Saves some time.