Entity: Require declaration of gravity and drag via abstract methods

this guarantees that subclasses will actually declare them.

[bc break]

src/entity/Entity.php

@@ -222,6 +222,8 @@ abstract class Entity{
 		$this->timings = Timings::getEntityTimings($this);
 
 		$this->size = $this->getInitialSizeInfo();
+		$this->drag = $this->getInitialDragMultiplier();
+		$this->gravity = $this->getInitialGravity();
 
 		$this->id = self::nextRuntimeId();
 		$this->server = $location->getWorld()->getServer();
@@ -257,6 +259,21 @@ abstract class Entity{
 
 	abstract protected function getInitialSizeInfo() : EntitySizeInfo;
 
+	/**
+	 * Returns the percentage by which the entity's velocity is reduced per tick when moving through air.
+	 * The entity's velocity is multiplied by 1 minus this value.
+	 *
+	 * @return float 0-1
+	 */
+	abstract protected function getInitialDragMultiplier() : float;
+
+	/**
+	 * Returns the downwards acceleration of the entity when falling, in blocks/tick².
+	 *
+	 * @return float minimum 0
+	 */
+	abstract protected function getInitialGravity() : float;
+
 	public function getNameTag() : string{
 		return $this->nameTag;
 	}

src/entity/Living.php

@@ -76,9 +76,6 @@ use const M_PI;
 abstract class Living extends Entity{
 	protected const DEFAULT_BREATH_TICKS = 300;
 
-	protected $gravity = 0.08;
-	protected $drag = 0.02;
-
 	/** @var int */
 	protected $attackTime = 0;
 
@@ -121,6 +118,10 @@ abstract class Living extends Entity{
 	/** @var bool */
 	protected $swimming = false;
 
+	protected function getInitialDragMultiplier() : float{ return 0.02; }
+
+	protected function getInitialGravity() : float{ return 0.08; }
+
 	abstract public function getName() : string;
 
 	protected function initEntity(CompoundTag $nbt) : void{

src/entity/object/ExperienceOrb.php

@@ -78,9 +78,6 @@ class ExperienceOrb extends Entity{
 		return $result;
 	}
 
-	public $gravity = 0.04;
-	public $drag = 0.02;
-
 	/** @var int */
 	protected $age = 0;
 
@@ -106,6 +103,10 @@ class ExperienceOrb extends Entity{
 
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.25, 0.25); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.02; }
+
+	protected function getInitialGravity() : float{ return 0.04; }
+
 	protected function initEntity(CompoundTag $nbt) : void{
 		parent::initEntity($nbt);
 

src/entity/object/FallingBlock.php

@@ -46,9 +46,6 @@ class FallingBlock extends Entity{
 
 	public static function getNetworkTypeId() : string{ return EntityIds::FALLING_BLOCK; }
 
-	protected $gravity = 0.04;
-	protected $drag = 0.02;
-
 	/** @var Block */
 	protected $block;
 
@@ -61,6 +58,10 @@ class FallingBlock extends Entity{
 
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.98, 0.98); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.02; }
+
+	protected function getInitialGravity() : float{ return 0.04; }
+
 	public static function parseBlockNBT(BlockFactory $factory, CompoundTag $nbt) : Block{
 		$blockId = 0;
 

src/entity/object/ItemEntity.php

@@ -59,9 +59,6 @@ class ItemEntity extends Entity{
 	/** @var Item */
 	protected $item;
 
-	protected $gravity = 0.04;
-	protected $drag = 0.02;
-
 	public $canCollide = false;
 
 	/** @var int */
@@ -77,6 +74,10 @@ class ItemEntity extends Entity{
 
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.25, 0.25); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.02; }
+
+	protected function getInitialGravity() : float{ return 0.04; }
+
 	protected function initEntity(CompoundTag $nbt) : void{
 		parent::initEntity($nbt);
 

src/entity/object/Painting.php

@@ -56,11 +56,6 @@ class Painting extends Entity{
 		Facing::EAST => 3
 	];
 
-	/** @var float */
-	protected $gravity = 0.0;
-	/** @var float */
-	protected $drag = 1.0;
-
 	/** @var Vector3 */
 	protected $blockIn;
 	/** @var int */
@@ -80,6 +75,10 @@ class Painting extends Entity{
 		return new EntitySizeInfo(0.5, 0.5);
 	}
 
+	protected function getInitialDragMultiplier() : float{ return 1.0; }
+
+	protected function getInitialGravity() : float{ return 0.0; }
+
 	protected function initEntity(CompoundTag $nbt) : void{
 		$this->setMaxHealth(1);
 		$this->setHealth(1);

src/entity/object/PrimedTNT.php

@@ -41,9 +41,6 @@ class PrimedTNT extends Entity implements Explosive{
 
 	public static function getNetworkTypeId() : string{ return EntityIds::TNT; }
 
-	protected $gravity = 0.04;
-	protected $drag = 0.02;
-
 	/** @var int */
 	protected $fuse;
 
@@ -53,6 +50,10 @@ class PrimedTNT extends Entity implements Explosive{
 
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.98, 0.98); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.02; }
+
+	protected function getInitialGravity() : float{ return 0.04; }
+
 	public function getFuse() : int{
 		return $this->fuse;
 	}

src/entity/projectile/Arrow.php

@@ -52,9 +52,6 @@ class Arrow extends Projectile{
 	private const TAG_PICKUP = "pickup"; //TAG_Byte
 	public const TAG_CRIT = "crit"; //TAG_Byte
 
-	protected $gravity = 0.05;
-	protected $drag = 0.01;
-
 	/** @var float */
 	protected $damage = 2.0;
 
@@ -77,6 +74,10 @@ class Arrow extends Projectile{
 
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.25, 0.25); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.01; }
+
+	protected function getInitialGravity() : float{ return 0.05; }
+
 	protected function initEntity(CompoundTag $nbt) : void{
 		parent::initEntity($nbt);
 

src/entity/projectile/ExperienceBottle.php

@@ -32,7 +32,7 @@ use function mt_rand;
 class ExperienceBottle extends Throwable{
 	public static function getNetworkTypeId() : string{ return EntityIds::XP_BOTTLE; }
 
-	protected $gravity = 0.07;
+	protected function getInitialGravity() : float{ return 0.07; }
 
 	public function getResultDamage() : int{
 		return -1;

src/entity/projectile/SplashPotion.php

@@ -52,9 +52,6 @@ class SplashPotion extends Throwable{
 
 	public static function getNetworkTypeId() : string{ return EntityIds::SPLASH_POTION; }
 
-	protected $gravity = 0.05;
-	protected $drag = 0.01;
-
 	/** @var bool */
 	protected $linger = false;
 	protected PotionType $potionType;
@@ -64,6 +61,8 @@ class SplashPotion extends Throwable{
 		parent::__construct($location, $shootingEntity, $nbt);
 	}
 
+	protected function getInitialGravity() : float{ return 0.05; }
+
 	public function saveNBT() : CompoundTag{
 		$nbt = parent::saveNBT();
 		$nbt->setShort("PotionId", PotionTypeIdMap::getInstance()->toId($this->getPotionType()));

src/entity/projectile/Throwable.php

@@ -29,11 +29,12 @@ use pocketmine\math\RayTraceResult;
 
 abstract class Throwable extends Projectile{
 
-	protected $gravity = 0.03;
-	protected $drag = 0.01;
-
 	protected function getInitialSizeInfo() : EntitySizeInfo{ return new EntitySizeInfo(0.25, 0.25); }
 
+	protected function getInitialDragMultiplier() : float{ return 0.01; }
+
+	protected function getInitialGravity() : float{ return 0.03; }
+
 	protected function onHitBlock(Block $blockHit, RayTraceResult $hitResult) : void{
 		parent::onHitBlock($blockHit, $hitResult);
 		$this->flagForDespawn();