Added a hack to allow tiles to trigger client-side render updates on blocks without actually changing the block

Bedrock block entity updates don't directly trigger block rendering
updates. This is a problem when the block entity data affects the
block's appearance directly (e.g. cauldron water colour, flower pot
contents), because it means changing them won't directly result in a
client-side render update.

This hack allows tiles to spoof block updates without actually changing
the server-side block, keeping the internals and API clean of random
shitbox workarounds.

fixes #5174
fixes #4944

src/block/tile/FlowerPot.php

@@ -27,7 +27,9 @@ use pocketmine\block\Air;
 use pocketmine\block\Block;
 use pocketmine\block\BlockFactory;
 use pocketmine\data\bedrock\block\BlockStateDeserializeException;
+use pocketmine\data\bedrock\block\BlockStateNames;
 use pocketmine\data\SavedDataLoadingException;
+use pocketmine\nbt\tag\ByteTag;
 use pocketmine\nbt\tag\CompoundTag;
 use pocketmine\nbt\tag\IntTag;
 use pocketmine\nbt\tag\ShortTag;
@@ -92,4 +94,8 @@ class FlowerPot extends Spawnable{
 			$nbt->setTag(self::TAG_PLANT_BLOCK, RuntimeBlockMapping::getInstance()->toStateData($this->plant->getStateId())->toNbt());
 		}
 	}
+
+	public function getRenderUpdateBugWorkaroundStateProperties(Block $block) : array{
+		return [BlockStateNames::UPDATE_BIT => new ByteTag(1)];
+	}
 }

src/block/tile/Spawnable.php

@@ -23,7 +23,11 @@ declare(strict_types=1);
 
 namespace pocketmine\block\tile;
 
+use pocketmine\block\Block;
+use pocketmine\nbt\tag\ByteTag;
 use pocketmine\nbt\tag\CompoundTag;
+use pocketmine\nbt\tag\IntTag;
+use pocketmine\nbt\tag\StringTag;
 use pocketmine\network\mcpe\protocol\types\CacheableNbt;
 use function get_class;
 
@@ -49,6 +53,22 @@ abstract class Spawnable extends Tile{
 		$this->spawnCompoundCache = null;
 	}
 
+	/**
+	 * The Bedrock client won't re-render a block if the block's state properties didn't change. This is a problem when
+	 * the tile may affect the block's appearance. For example, a cauldron's liquid changes colour based on the dye
+	 * inside.
+	 *
+	 * This is worked around in vanilla by modifying one of the block's state properties to a different value, and then
+	 * changing it back again. Since we don't want to litter core implementation with hacks like this, we brush it under
+	 * the rug into Tile.
+	 *
+	 * @return ByteTag[]|IntTag[]|StringTag[]
+	 * @phpstan-return array<string, IntTag|StringTag|ByteTag>
+	 */
+	public function getRenderUpdateBugWorkaroundStateProperties(Block $block) : array{
+		return [];
+	}
+
 	/**
 	 * Returns encoded NBT (varint, little-endian) used to spawn this tile to clients. Uses cache where possible,
 	 * populates cache if it is null.

src/data/bedrock/block/convert/BlockObjectToBlockStateSerializer.php

@@ -907,7 +907,7 @@ final class BlockObjectToBlockStateSerializer implements BlockStateSerializer{
 		});
 		$this->map(Blocks::FLOWER_POT(), function() : Writer{
 			return Writer::create(Ids::FLOWER_POT)
-				->writeBool(StateNames::UPDATE_BIT, true); //to keep MCPE happy
+				->writeBool(StateNames::UPDATE_BIT, false); //to keep MCPE happy
 		});
 		$this->map(Blocks::FROSTED_ICE(), function(FrostedIce $block) : Writer{
 			return Writer::create(Ids::FROSTED_ICE)

src/world/World.php

@@ -36,6 +36,7 @@ use pocketmine\block\tile\TileFactory;
 use pocketmine\block\UnknownBlock;
 use pocketmine\block\VanillaBlocks;
 use pocketmine\data\bedrock\BiomeIds;
+use pocketmine\data\bedrock\block\BlockStateData;
 use pocketmine\data\SavedDataLoadingException;
 use pocketmine\entity\Entity;
 use pocketmine\entity\EntityFactory;
@@ -948,6 +949,22 @@ class World implements ChunkManager{
 
 			$fullBlock = $this->getBlockAt($b->x, $b->y, $b->z);
 			$blockPosition = BlockPosition::fromVector3($b);
+
+			$tile = $this->getTileAt($b->x, $b->y, $b->z);
+			if($tile instanceof Spawnable && ($fakeStateProperties = $tile->getRenderUpdateBugWorkaroundStateProperties($fullBlock)) !== null){
+				$originalStateData = $blockMapping->toStateData($fullBlock->getStateId());
+				$fakeStateData = new BlockStateData(
+					$originalStateData->getName(),
+					array_merge($originalStateData->getStates(), $fakeStateProperties),
+					$originalStateData->getVersion()
+				);
+				$packets[] = UpdateBlockPacket::create(
+					$blockPosition,
+					$blockMapping->getBlockStateDictionary()->lookupStateIdFromData($fakeStateData) ?? throw new AssumptionFailedError("Unmapped fake blockstate data: " . $fakeStateData->toNbt()),
+					UpdateBlockPacket::FLAG_NETWORK,
+					UpdateBlockPacket::DATA_LAYER_NORMAL
+				);
+			}
 			$packets[] = UpdateBlockPacket::create(
 				$blockPosition,
 				$blockMapping->toRuntimeId($fullBlock->getStateId()),
@@ -955,7 +972,6 @@ class World implements ChunkManager{
 				UpdateBlockPacket::DATA_LAYER_NORMAL
 			);
 
-			$tile = $this->getTileAt($b->x, $b->y, $b->z);
 			if($tile instanceof Spawnable){
 				$packets[] = BlockActorDataPacket::create($blockPosition, $tile->getSerializedSpawnCompound());
 			}