Mapgen V6: Add flag to stop mud flow

src/mapgen.cpp

@@ -47,6 +47,7 @@ FlagDesc flagdesc_mapgen[] = {
 	{"v6_biome_blend", MGV6_BIOME_BLEND},
 	{"flat",           MG_FLAT},
 	{"nolight",        MG_NOLIGHT},
+	{"v6_nomudflow",   MGV6_NOMUDFLOW},
 	{NULL,             0}
 };
 

src/mapgen.h

@@ -38,6 +38,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #define MG_NOLIGHT       0x40
 #define MGV7_MOUNTAINS   0x80
 #define MGV7_RIDGES      0x100
+#define MGV6_NOMUDFLOW   0x200
 
 /////////////////// Ore generation flags
 // Use absolute value of height to determine ore placement

src/mapgen_v6.cpp

@@ -439,6 +439,7 @@ void MapgenV6::makeChunk(BlockMakeData *data) {
 		addDirtGravelBlobs();
 
 		// Flow mud away from steep edges
+		if (!(flags & MGV6_NOMUDFLOW))
 			flowMud(mudflow_minpos, mudflow_maxpos);
 
 	}