Move Mapgen V7 river generation into the main generation loop (#10639)

All terrain generation now occurs in one loop, instead of rivers being
carved afterwards in a separate loop.
Fixes the removal of nodes added by mods in 'register on generated'.
Avoids other problems and reduces the chance of future bugs.
Mapchunk generation time is reduced.

Also fixes a code mistake which resulted in river channel generation
being disabled at floatland altitudes even when floatlands were disabled.

src/mapgen/mapgen_v7.cpp

@@ -342,10 +342,6 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 	// Generate base and mountain terrain
 	s16 stone_surface_max_y = generateTerrain();
 
-	// Generate rivers
-	if (spflags & MGV7_RIDGES)
-		generateRidgeTerrain();
-
 	// Create heightmap
 	updateHeightmap(node_min, node_max);
 
@@ -467,6 +463,23 @@ bool MapgenV7::getMountainTerrainFromMap(int idx_xyz, int idx_xz, s16 y)
 }
 
 
+bool MapgenV7::getRiverChannelFromMap(int idx_xyz, int idx_xz, s16 y)
+{
+	// Maximum width of river channel. Creates the vertical canyon walls
+	float width = 0.2f;
+	float absuwatern = std::fabs(noise_ridge_uwater->result[idx_xz]) * 2.0f;
+	if (absuwatern > width)
+		return false;
+
+	float altitude = y - water_level;
+	float height_mod = (altitude + 17.0f) / 2.5f;
+	float width_mod = width - absuwatern;
+	float nridge = noise_ridge->result[idx_xyz] * std::fmax(altitude, 0.0f) / 7.0f;
+
+	return nridge + width_mod * height_mod >= 0.6f;
+}
+
+
 bool MapgenV7::getFloatlandTerrainFromMap(int idx_xyz, float float_offset)
 {
 	return noise_floatland->result[idx_xyz] + floatland_density - float_offset >= 0.0f;
@@ -521,6 +534,15 @@ int MapgenV7::generateTerrain()
 		}
 	}
 
+	// 'Generate rivers in this mapchunk' bool for
+	// simplification of condition checks in y-loop.
+	bool gen_rivers = (spflags & MGV7_RIDGES) && node_max.Y >= water_level - 16 &&
+		!gen_floatlands;
+	if (gen_rivers) {
+		noise_ridge->perlinMap3D(node_min.X, node_min.Y - 1, node_min.Z);
+		noise_ridge_uwater->perlinMap2D(node_min.X, node_min.Z);
+	}
+
 	//// Place nodes
 	const v3s16 &em = vm->m_area.getExtent();
 	s16 stone_surface_max_y = -MAX_MAP_GENERATION_LIMIT;
@@ -544,10 +566,13 @@ int MapgenV7::generateTerrain()
 			if (vm->m_data[vi].getContent() != CONTENT_IGNORE)
 				continue;
 
-			if (y <= surface_y) {
+			bool is_river_channel = gen_rivers &&
+				getRiverChannelFromMap(index3d, index2d, y);
+			if (y <= surface_y && !is_river_channel) {
 				vm->m_data[vi] = n_stone; // Base terrain
 			} else if ((spflags & MGV7_MOUNTAINS) &&
-					getMountainTerrainFromMap(index3d, index2d, y)) {
+					getMountainTerrainFromMap(index3d, index2d, y) &&
+					!is_river_channel) {
 				vm->m_data[vi] = n_stone; // Mountain terrain
 				if (y > stone_surface_max_y)
 					stone_surface_max_y = y;
@@ -569,45 +594,3 @@ int MapgenV7::generateTerrain()
 
 	return stone_surface_max_y;
 }
-
-
-void MapgenV7::generateRidgeTerrain()
-{
-	if (node_max.Y < water_level - 16 ||
-			(node_max.Y >= floatland_ymin && node_min.Y <= floatland_ymax))
-		return;
-
-	noise_ridge->perlinMap3D(node_min.X, node_min.Y - 1, node_min.Z);
-	noise_ridge_uwater->perlinMap2D(node_min.X, node_min.Z);
-
-	MapNode n_water(c_water_source);
-	MapNode n_air(CONTENT_AIR);
-	u32 index3d = 0;
-	float width = 0.2f;
-
-	for (s16 z = node_min.Z; z <= node_max.Z; z++)
-	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++, index3d++, vi++) {
-			u32 index2d = (z - node_min.Z) * csize.X + (x - node_min.X);
-			float uwatern = noise_ridge_uwater->result[index2d] * 2.0f;
-			if (std::fabs(uwatern) > width)
-				continue;
-			// Optimises, but also avoids removing nodes placed by mods in
-			// 'on-generated', when generating outside mapchunk.
-			content_t c = vm->m_data[vi].getContent();
-			if (c != c_stone)
-				continue;
-
-			float altitude = y - water_level;
-			float height_mod = (altitude + 17.0f) / 2.5f;
-			float width_mod = width - std::fabs(uwatern);
-			float nridge = noise_ridge->result[index3d] *
-				std::fmax(altitude, 0.0f) / 7.0f;
-			if (nridge + width_mod * height_mod < 0.6f)
-				continue;
-
-			vm->m_data[vi] = (y > water_level) ? n_air : n_water;
-		}
-	}
-}

src/mapgen/mapgen_v7.h

@@ -94,10 +94,10 @@ public:
 	float baseTerrainLevelFromMap(int index);
 	bool getMountainTerrainAtPoint(s16 x, s16 y, s16 z);
 	bool getMountainTerrainFromMap(int idx_xyz, int idx_xz, s16 y);
+	bool getRiverChannelFromMap(int idx_xyz, int idx_xz, s16 y);
 	bool getFloatlandTerrainFromMap(int idx_xyz, float float_offset);
 
 	int generateTerrain();
-	void generateRidgeTerrain();
 
 private:
 	s16 mount_zero_level;