Limit SubChunk to 2 layers, avoid arrays (#6747)

Initially proposed in #6575

This shows about a 10% performance improvement to both SubChunk->getBlockStateId() and SubChunk->setBlockStateId(), so definitely worth doing. It does result in increased complexity, but for a double digits performance gain, I think it's worth it.

Closes #6575

src/world/format/Chunk.php

@@ -73,7 +73,7 @@ class Chunk{
 
 		foreach($this->subChunks as $y => $null){
 			//TODO: we should probably require all subchunks to be provided here
-			$this->subChunks[$y] = $subChunks[$y + self::MIN_SUBCHUNK_INDEX] ?? new SubChunk(Block::EMPTY_STATE_ID, [], new PalettedBlockArray(BiomeIds::OCEAN));
+			$this->subChunks[$y] = $subChunks[$y + self::MIN_SUBCHUNK_INDEX] ?? new SubChunk(Block::EMPTY_STATE_ID, null, null, new PalettedBlockArray(BiomeIds::OCEAN));
 		}
 
 		$val = (self::MAX_SUBCHUNK_INDEX + 1) * SubChunk::EDGE_LENGTH;
@@ -298,7 +298,7 @@ class Chunk{
 			throw new \InvalidArgumentException("Invalid subchunk Y coordinate $y");
 		}
 
-		$this->subChunks[$y - self::MIN_SUBCHUNK_INDEX] = $subChunk ?? new SubChunk(Block::EMPTY_STATE_ID, [], new PalettedBlockArray(BiomeIds::OCEAN));
+		$this->subChunks[$y - self::MIN_SUBCHUNK_INDEX] = $subChunk ?? new SubChunk(Block::EMPTY_STATE_ID, null, null, new PalettedBlockArray(BiomeIds::OCEAN));
 		$this->terrainDirtyFlags |= self::DIRTY_FLAG_BLOCKS;
 	}
 

src/world/format/SubChunk.php

@@ -23,9 +23,6 @@ declare(strict_types=1);
 
 namespace pocketmine\world\format;
 
-use function array_map;
-use function count;
-
 class SubChunk{
 	public const COORD_BIT_SIZE = 4;
 	public const COORD_MASK = ~(~0 << self::COORD_BIT_SIZE);
@@ -33,13 +30,11 @@ class SubChunk{
 
 	/**
 	 * SubChunk constructor.
-	 *
-	 * @param PalettedBlockArray[] $blockLayers
-	 * @phpstan-param list<PalettedBlockArray> $blockLayers
 	 */
 	public function __construct(
 		private int $emptyBlockId,
-		private array $blockLayers,
+		private ?PalettedBlockArray $blockLayer0,
+		private ?PalettedBlockArray $blockLayer1,
 		private PalettedBlockArray $biomes,
 		private ?LightArray $skyLight = null,
 		private ?LightArray $blockLight = null
@@ -60,7 +55,7 @@ class SubChunk{
 	 * This may report non-empty erroneously if the chunk has been modified and not garbage-collected.
 	 */
 	public function isEmptyFast() : bool{
-		return count($this->blockLayers) === 0;
+		return $this->blockLayer0 === null && $this->blockLayer1 === null;
 	}
 
 	/**
@@ -70,33 +65,45 @@ class SubChunk{
 	public function getEmptyBlockId() : int{ return $this->emptyBlockId; }
 
 	public function getBlockStateId(int $x, int $y, int $z) : int{
-		if(count($this->blockLayers) === 0){
-			return $this->emptyBlockId;
-		}
-		return $this->blockLayers[0]->get($x, $y, $z);
+		return $this->blockLayer0?->get($x, $y, $z) ?? $this->emptyBlockId;
 	}
 
 	public function setBlockStateId(int $x, int $y, int $z, int $block) : void{
-		if(count($this->blockLayers) === 0){
-			$this->blockLayers[] = new PalettedBlockArray($this->emptyBlockId);
+		if($this->blockLayer0 === null){
+			$this->blockLayer0 = new PalettedBlockArray($this->emptyBlockId);
 		}
-		$this->blockLayers[0]->set($x, $y, $z, $block);
+		$this->blockLayer0->set($x, $y, $z, $block);
+	}
+
+	public function getBlockLayer0() : ?PalettedBlockArray{
+		return $this->blockLayer0;
+	}
+
+	public function getBlockLayer1() : ?PalettedBlockArray{
+		return $this->blockLayer1;
 	}
 
 	/**
 	 * @return PalettedBlockArray[]
-	 * @phpstan-return list<PalettedBlockArray>
+	 * @phpstan-return array{}|array{PalettedBlockArray}|array{PalettedBlockArray, PalettedBlockArray}
 	 */
 	public function getBlockLayers() : array{
-		return $this->blockLayers;
+		$layers = [];
+		if($this->blockLayer0 !== null){
+			$layers[] = $this->blockLayer0;
+		}
+		if($this->blockLayer1 !== null){
+			$layers[] = $this->blockLayer1;
+		}
+		return $layers;
 	}
 
 	public function getHighestBlockAt(int $x, int $z) : ?int{
-		if(count($this->blockLayers) === 0){
+		if($this->blockLayer0 === null){
 			return null;
 		}
 		for($y = self::EDGE_LENGTH - 1; $y >= 0; --$y){
-			if($this->blockLayers[0]->get($x, $y, $z) !== $this->emptyBlockId){
+			if($this->blockLayer0->get($x, $y, $z) !== $this->emptyBlockId){
 				return $y;
 			}
 		}
@@ -129,16 +136,21 @@ class SubChunk{
 		return [];
 	}
 
-	public function collectGarbage() : void{
-		$cleanedLayers = [];
-		foreach($this->blockLayers as $layer){
-			$layer->collectGarbage();
-
-			if($layer->getBitsPerBlock() !== 0 || $layer->get(0, 0, 0) !== $this->emptyBlockId){
-				$cleanedLayers[] = $layer;
-			}
+	private static function gcBlockPalette(?PalettedBlockArray $layer, int $emptyBlockId) : ?PalettedBlockArray{
+		if($layer === null){
+			return null;
+		}
+		$layer->collectGarbage();
+		return $layer->getBitsPerBlock() === 0 && $layer->get(0, 0, 0) === $emptyBlockId ? null : $layer;
+	}
+
+	public function collectGarbage() : void{
+		$this->blockLayer0 = self::gcBlockPalette($this->blockLayer0, $this->emptyBlockId);
+		$this->blockLayer1 = self::gcBlockPalette($this->blockLayer1, $this->emptyBlockId);
+		if($this->blockLayer0 === null && $this->blockLayer1 !== null){
+			$this->blockLayer0 = $this->blockLayer1;
+			$this->blockLayer1 = null;
 		}
-		$this->blockLayers = $cleanedLayers;
 		$this->biomes->collectGarbage();
 
 		if($this->skyLight !== null && $this->skyLight->isUniform(0)){
@@ -150,9 +162,8 @@ class SubChunk{
 	}
 
 	public function __clone(){
-		$this->blockLayers = array_map(function(PalettedBlockArray $array) : PalettedBlockArray{
-			return clone $array;
-		}, $this->blockLayers);
+		$this->blockLayer0 = $this->blockLayer0 !== null ? clone $this->blockLayer0 : null;
+		$this->blockLayer1 = $this->blockLayer1 !== null ? clone $this->blockLayer1 : null;
 		$this->biomes = clone $this->biomes;
 
 		if($this->skyLight !== null){

src/world/format/io/FastChunkSerializer.php

@@ -81,7 +81,6 @@ final class FastChunkSerializer{
 				self::serializePalettedArray($stream, $blocks);
 			}
 			self::serializePalettedArray($stream, $subChunk->getBiomeArray());
-
 		}
 
 		return $stream->getData();
@@ -115,12 +114,15 @@ final class FastChunkSerializer{
 			//TODO: why the heck are we using big-endian here?
 			$airBlockId = BE::readUnsignedInt($stream);
 
-			$layers = [];
-			for($i = 0, $layerCount = Byte::readUnsigned($stream); $i < $layerCount; ++$i){
-				$layers[] = self::deserializePalettedArray($stream);
+			$layerCount = Byte::readUnsigned($stream);
+			if($layerCount > 2){
+				throw new \UnexpectedValueException("Expected at most 2 layers, but got $layerCount");
 			}
+			$layer0 = $layerCount >= 1 ? self::deserializePalettedArray($stream) : null;
+			$layer1 = $layerCount === 2 ? self::deserializePalettedArray($stream) : null;
+
 			$biomeArray = self::deserializePalettedArray($stream);
-			$subChunks[$y] = new SubChunk($airBlockId, $layers, $biomeArray);
+			$subChunks[$y] = new SubChunk($airBlockId, $layer0, $layer1, $biomeArray);
 		}
 
 		return new Chunk($subChunks, $terrainPopulated);

src/world/format/io/leveldb/LevelDB.php

@@ -462,17 +462,15 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 
 		$subChunks = [];
 		for($yy = 0; $yy < 8; ++$yy){
-			$storages = [$this->palettizeLegacySubChunkFromColumn($fullIds, $fullData, $yy, new \PrefixedLogger($logger, "Subchunk y=$yy"))];
-			if(isset($convertedLegacyExtraData[$yy])){
-				$storages[] = $convertedLegacyExtraData[$yy];
-			}
-			$subChunks[$yy] = new SubChunk(Block::EMPTY_STATE_ID, $storages, clone $biomes3d);
+			$layer0 = $this->palettizeLegacySubChunkFromColumn($fullIds, $fullData, $yy, new \PrefixedLogger($logger, "Subchunk y=$yy"));
+			$layer1 = $convertedLegacyExtraData[$yy] ?? null;
+			$subChunks[$yy] = new SubChunk(Block::EMPTY_STATE_ID, $layer0, $layer1, clone $biomes3d);
 		}
 
 		//make sure extrapolated biomes get filled in correctly
 		for($yy = Chunk::MIN_SUBCHUNK_INDEX; $yy <= Chunk::MAX_SUBCHUNK_INDEX; ++$yy){
 			if(!isset($subChunks[$yy])){
-				$subChunks[$yy] = new SubChunk(Block::EMPTY_STATE_ID, [], clone $biomes3d);
+				$subChunks[$yy] = new SubChunk(Block::EMPTY_STATE_ID, null, null, clone $biomes3d);
 			}
 		}
 
@@ -501,12 +499,10 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 			}
 		}
 
-		$storages = [$this->palettizeLegacySubChunkXZY($blocks, $blockData, $logger)];
-		if($convertedLegacyExtraData !== null){
-			$storages[] = $convertedLegacyExtraData;
-		}
+		$layer0 = $this->palettizeLegacySubChunkXZY($blocks, $blockData, $logger);
+		$layer1 = $convertedLegacyExtraData;
 
-		return new SubChunk(Block::EMPTY_STATE_ID, $storages, $biomePalette);
+		return new SubChunk(Block::EMPTY_STATE_ID, $layer0, $layer1, $biomePalette);
 	}
 
 	/**
@@ -526,11 +522,9 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 			case SubChunkVersion::CLASSIC_BUG_7:
 				return $this->deserializeNonPalettedSubChunkData($binaryStream, $chunkVersion, $convertedLegacyExtraData, $biomePalette, $logger);
 			case SubChunkVersion::PALETTED_SINGLE:
-				$storages = [$this->deserializeBlockPalette($binaryStream, $logger)];
-				if($convertedLegacyExtraData !== null){
-					$storages[] = $convertedLegacyExtraData;
-				}
-				return new SubChunk(Block::EMPTY_STATE_ID, $storages, $biomePalette);
+				$layer0 = $this->deserializeBlockPalette($binaryStream, $logger);
+				$layer1 = $convertedLegacyExtraData;
+				return new SubChunk(Block::EMPTY_STATE_ID, $layer0, $layer1, $biomePalette);
 			case SubChunkVersion::PALETTED_MULTI:
 			case SubChunkVersion::PALETTED_MULTI_WITH_OFFSET:
 				//legacy extradata layers intentionally ignored because they aren't supposed to exist in v8
@@ -541,11 +535,18 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 					$binaryStream->getByte();
 				}
 
-				$storages = [];
+				$layer0 = null;
+				$layer1 = null;
 				for($k = 0; $k < $storageCount; ++$k){
-					$storages[] = $this->deserializeBlockPalette($binaryStream, $logger);
+					$layer = $this->deserializeBlockPalette($binaryStream, $logger);
+					if($k === 0){
+						$layer0 = $layer;
+					}elseif($k === 1){
+						$layer1 = $layer;
+					}
+					// Ignore additional layers beyond the first two
 				}
-				return new SubChunk(Block::EMPTY_STATE_ID, $storages, $biomePalette);
+				return new SubChunk(Block::EMPTY_STATE_ID, $layer0, $layer1, $biomePalette);
 			default:
 				//this should never happen - an unsupported chunk appearing in a supported world is a sign of corruption
 				throw new CorruptedChunkException("don't know how to decode LevelDB subchunk format version $subChunkVersion");
@@ -575,7 +576,7 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 		$subChunkKeyOffset = self::hasOffsetCavesAndCliffsSubChunks($chunkVersion) ? self::CAVES_CLIFFS_EXPERIMENTAL_SUBCHUNK_KEY_OFFSET : 0;
 		for($y = Chunk::MIN_SUBCHUNK_INDEX; $y <= Chunk::MAX_SUBCHUNK_INDEX; ++$y){
 			if(($data = $this->db->get($index . ChunkDataKey::SUBCHUNK . chr($y + $subChunkKeyOffset))) === false){
-				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, [], $biomeArrays[$y]);
+				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, null, null, $biomeArrays[$y]);
 				continue;
 			}
 
@@ -776,8 +777,8 @@ class LevelDB extends BaseWorldProvider implements WritableWorldProvider{
 
 					$layers = $subChunk->getBlockLayers();
 					$subStream->putByte(count($layers));
-					foreach($layers as $blocks){
-						$this->serializeBlockPalette($subStream, $blocks);
+					foreach($layers as $layer){
+						$this->serializeBlockPalette($subStream, $layer);
 					}
 
 					$write->put($key, $subStream->getBuffer());

src/world/format/io/region/Anvil.php

@@ -32,11 +32,11 @@ class Anvil extends RegionWorldProvider{
 	use LegacyAnvilChunkTrait;
 
 	protected function deserializeSubChunk(CompoundTag $subChunk, PalettedBlockArray $biomes3d, \Logger $logger) : SubChunk{
-		return new SubChunk(Block::EMPTY_STATE_ID, [$this->palettizeLegacySubChunkYZX(
+		return new SubChunk(Block::EMPTY_STATE_ID, $this->palettizeLegacySubChunkYZX(
 			self::readFixedSizeByteArray($subChunk, "Blocks", 4096),
 			self::readFixedSizeByteArray($subChunk, "Data", 2048),
 			$logger
-		)], $biomes3d);
+		), null, $biomes3d);
 		//ignore legacy light information
 	}
 

src/world/format/io/region/LegacyAnvilChunkTrait.php

@@ -94,7 +94,7 @@ trait LegacyAnvilChunkTrait{
 		}
 		for($y = Chunk::MIN_SUBCHUNK_INDEX; $y <= Chunk::MAX_SUBCHUNK_INDEX; ++$y){
 			if(!isset($subChunks[$y])){
-				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, [], clone $biomes3d);
+				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, null, null, clone $biomes3d);
 			}
 		}
 

src/world/format/io/region/McRegion.php

@@ -90,16 +90,17 @@ class McRegion extends RegionWorldProvider{
 		$fullData = self::readFixedSizeByteArray($chunk, "Data", 16384);
 
 		for($y = 0; $y < 8; ++$y){
-			$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, [$this->palettizeLegacySubChunkFromColumn(
+			$blockLayer = $this->palettizeLegacySubChunkFromColumn(
 				$fullIds,
 				$fullData,
 				$y,
 				new \PrefixedLogger($logger, "Subchunk y=$y"),
-			)], clone $biomes3d);
+			);
+			$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, $blockLayer, null, clone $biomes3d);
 		}
 		for($y = Chunk::MIN_SUBCHUNK_INDEX; $y <= Chunk::MAX_SUBCHUNK_INDEX; ++$y){
 			if(!isset($subChunks[$y])){
-				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, [], clone $biomes3d);
+				$subChunks[$y] = new SubChunk(Block::EMPTY_STATE_ID, null, null, clone $biomes3d);
 			}
 		}
 

src/world/format/io/region/PMAnvil.php

@@ -36,11 +36,11 @@ class PMAnvil extends RegionWorldProvider{
 	use LegacyAnvilChunkTrait;
 
 	protected function deserializeSubChunk(CompoundTag $subChunk, PalettedBlockArray $biomes3d, \Logger $logger) : SubChunk{
-		return new SubChunk(Block::EMPTY_STATE_ID, [$this->palettizeLegacySubChunkXZY(
+		return new SubChunk(Block::EMPTY_STATE_ID, $this->palettizeLegacySubChunkXZY(
 			self::readFixedSizeByteArray($subChunk, "Blocks", 4096),
 			self::readFixedSizeByteArray($subChunk, "Data", 2048),
 			$logger
-		)], $biomes3d);
+		), null, $biomes3d);
 	}
 
 	protected static function getRegionFileExtension() : string{

src/world/light/BlockLightUpdate.php

@@ -24,6 +24,7 @@ declare(strict_types=1);
 namespace pocketmine\world\light;
 
 use pocketmine\world\format\LightArray;
+use pocketmine\world\format\PalettedBlockArray;
 use pocketmine\world\format\SubChunk;
 use pocketmine\world\utils\SubChunkExplorer;
 use pocketmine\world\utils\SubChunkExplorerStatus;
@@ -55,6 +56,20 @@ class BlockLightUpdate extends LightUpdate{
 		}
 	}
 
+	private function layerHasLightEmitter(?PalettedBlockArray $layer) : bool{
+		if($layer === null){
+			return false;
+		}
+
+		foreach($layer->getPalette() as $state){
+			if(($this->lightEmitters[$state] ?? 0) > 0){
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	public function recalculateChunk(int $chunkX, int $chunkZ) : int{
 		if($this->subChunkExplorer->moveToChunk($chunkX, 0, $chunkZ) === SubChunkExplorerStatus::INVALID){
 			throw new \InvalidArgumentException("Chunk $chunkX $chunkZ does not exist");
@@ -65,13 +80,11 @@ class BlockLightUpdate extends LightUpdate{
 		foreach($chunk->getSubChunks() as $subChunkY => $subChunk){
 			$subChunk->setBlockLightArray(LightArray::fill(0));
 
-			foreach($subChunk->getBlockLayers() as $layer){
-				foreach($layer->getPalette() as $state){
-					if(($this->lightEmitters[$state] ?? 0) > 0){
-						$lightSources += $this->scanForLightEmittingBlocks($subChunk, $chunkX << SubChunk::COORD_BIT_SIZE, $subChunkY << SubChunk::COORD_BIT_SIZE, $chunkZ << SubChunk::COORD_BIT_SIZE);
-						break 2;
-					}
-				}
+			if(
+				$this->layerHasLightEmitter($subChunk->getBlockLayer0()) ||
+				$this->layerHasLightEmitter($subChunk->getBlockLayer1())
+			){
+				$lightSources += $this->scanForLightEmittingBlocks($subChunk, $chunkX << SubChunk::COORD_BIT_SIZE, $subChunkY << SubChunk::COORD_BIT_SIZE, $chunkZ << SubChunk::COORD_BIT_SIZE);
 			}
 		}
 

tests/phpunit/world/format/SubChunkTest.php

@@ -32,7 +32,7 @@ class SubChunkTest extends TestCase{
 	 * Test that a cloned SubChunk instance doesn't influence the original
 	 */
 	public function testClone() : void{
-		$sub1 = new SubChunk(0, [], new PalettedBlockArray(BiomeIds::OCEAN));
+		$sub1 = new SubChunk(0, null, null, new PalettedBlockArray(BiomeIds::OCEAN));
 
 		$sub1->setBlockStateId(0, 0, 0, 1);
 		$sub1->getBlockLightArray()->set(0, 0, 0, 1);