Caverns: Remove unnecessary liquid excavation

Also disable CavesRandomWalk at a safer distance from caverns.

Excavating liquids in cavern code is unnecessary as in practice we are already
successfully disabling the generation of liquid caves that could intersect
with caverns and cause excessive amounts of spreading liquids in caverns.

However to be safer this commit now disables liquid caves at a larger distance
from caverns, to compensate for liquid caves being able to generate up to a
mapblock beyond a mapchunk border.

Not excavating liquids in cavern code also allows a feature i am working on in
experimental new core mapgens, but also allows for more flexibility in future.

3 files changed, 20 insertions, 18 deletions

diff --git a/src/cavegen.cpp b/src/cavegen.cpp
index 7993b20e7..dbed79951 100644
--- a/src/cavegen.cpp
+++ b/src/cavegen.cpp
@@ -160,9 +160,9 @@ CavernsNoise::CavernsNoise(
 {
 	assert(nodedef);
 
-	m_ndef = nodedef;
+	m_ndef  = nodedef;
 
-	m_csize = chunksize;
+	m_csize            = chunksize;
 	m_cavern_limit     = cavern_limit;
 	m_cavern_taper     = cavern_taper;
 	m_cavern_threshold = cavern_threshold;
@@ -207,7 +207,7 @@ bool CavernsNoise::generateCaverns(MMVManip *vm, v3s16 nmin, v3s16 nmax)
 	}
 
 	//// Place nodes
-	bool has_cavern = false;
+	bool near_cavern = false;
 	v3s16 em = vm->m_area.getExtent();
 	u32 index2d = 0;
 
@@ -229,20 +229,22 @@ bool CavernsNoise::generateCaverns(MMVManip *vm, v3s16 nmin, v3s16 nmax)
 				vm->m_area.add_y(em, vi, -1),
 				cavern_amp_index++) {
 			content_t c = vm->m_data[vi].getContent();
-			float nabs_cavern = fabs(noise_cavern->result[index3d]);
-			// Caverns generate first but still remove lava and water in case
-			// of overgenerated classic caves.
-			if (nabs_cavern * cavern_amp[cavern_amp_index] > m_cavern_threshold &&
-					(m_ndef->get(c).is_ground_content ||
-					c == c_lava_source || c == c_water_source)) {
-				vm->m_data[vi] = MapNode(CONTENT_AIR);
-				has_cavern = true;
+			float n_absamp_cavern = fabs(noise_cavern->result[index3d]) *
+				cavern_amp[cavern_amp_index];
+			// Disable CavesRandomWalk at a safe distance from caverns
+			// to avoid excessively spreading liquids in caverns.
+			if (n_absamp_cavern > m_cavern_threshold - 0.1f) {
+				near_cavern = true;
+				if (n_absamp_cavern > m_cavern_threshold &&
+						m_ndef->get(c).is_ground_content)
+					vm->m_data[vi] = MapNode(CONTENT_AIR);
 			}
 		}
 	}
 
 	delete[] cavern_amp;
-	return has_cavern;
+
+	return near_cavern;
 }
 
 
diff --git a/src/mapgen_v5.cpp b/src/mapgen_v5.cpp
index c7079d229..1c4d1fd70 100644
--- a/src/mapgen_v5.cpp
+++ b/src/mapgen_v5.cpp
@@ -204,12 +204,12 @@ void MapgenV5::makeChunk(BlockMakeData *data)
 
 	// Generate caverns, tunnels and classic caves
 	if (flags & MG_CAVES) {
-		bool has_cavern = false;
+		bool near_cavern = false;
 		// Generate caverns
 		if (spflags & MGV5_CAVERNS)
-			has_cavern = generateCaverns(stone_surface_max_y);
+			near_cavern = generateCaverns(stone_surface_max_y);
 		// Generate tunnels and classic caves
-		if (has_cavern)
+		if (near_cavern)
 			// Disable classic caves in this mapchunk by setting
 			// 'large cave depth' to world base. Avoids excessive liquid in
 			// large caverns and floating blobs of overgenerated liquid.
diff --git a/src/mapgen_v7.cpp b/src/mapgen_v7.cpp
index 420d77185..dbf2b02ae 100644
--- a/src/mapgen_v7.cpp
+++ b/src/mapgen_v7.cpp
@@ -292,12 +292,12 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 
 	// Generate caverns, tunnels and classic caves
 	if (flags & MG_CAVES) {
-		bool has_cavern = false;
+		bool near_cavern = false;
 		// Generate caverns
 		if (spflags & MGV7_CAVERNS)
-			has_cavern = generateCaverns(stone_surface_max_y);
+			near_cavern = generateCaverns(stone_surface_max_y);
 		// Generate tunnels and classic caves
-		if (has_cavern)
+		if (near_cavern)
 			// Disable classic caves in this mapchunk by setting
 			// 'large cave depth' to world base. Avoids excessive liquid in
 			// large caverns and floating blobs of overgenerated liquid.