Merge pull request #344 from Kebab11noel/fix/gravity

Fix gravity

src/main/java/net/minestom/server/entity/Entity.java

@@ -95,9 +95,18 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
     protected Vector velocity = new Vector(); // Movement in block per second
     protected boolean hasPhysics = true;
 
+    /**
+     * The amount of drag applied on the Y axle.
+     * <p>
+     * Unit: 1/tick
+     */
     protected double gravityDragPerTick;
+    /**
+     * Acceleration on the Y axle due to gravity
+     * <p>
+     * Unit: blocks/tick
+     */
     protected double gravityAcceleration;
-    protected double gravityTerminalVelocity;
     protected int gravityTickCount; // Number of tick where gravity tick was applied
 
     private boolean autoViewable;
@@ -162,6 +171,8 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
         Entity.ENTITY_BY_UUID.put(uuid, this);
 
         this.eventNode = EventNode.value("entity-" + uuid, EventFilter.ENTITY, this::equals);
+
+        initializeDefaultGravity();
     }
 
     public Entity(@NotNull EntityType entityType) {
@@ -527,13 +538,11 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
                 Vector newVelocityOut = new Vector();
 
                 // Gravity force
-                final double gravityY = !hasNoGravity() ? Math.min(
-                        gravityDragPerTick + (gravityAcceleration * (double) gravityTickCount),
-                        gravityTerminalVelocity) : 0;
+                final double gravityY = hasNoGravity() ? 0 : gravityAcceleration;
 
                 final Vector deltaPos = new Vector(
                         getVelocity().getX() / tps,
-                        (getVelocity().getY() - gravityY) / tps,
+                        getVelocity().getY() / tps - gravityY,
                         getVelocity().getZ() / tps
                 );
 
@@ -594,6 +603,8 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
 
                     this.velocity.setX(velocity.getX() * drag);
                     this.velocity.setZ(velocity.getZ() * drag);
+                    if (!hasNoGravity())
+                        this.velocity.setY(velocity.getY() * (1-gravityDragPerTick));
 
                     if (velocity.equals(new Vector())) {
                         this.velocity.zero();
@@ -985,15 +996,6 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
         return gravityAcceleration;
     }
 
-    /**
-     * Gets the maximum gravity velocity.
-     *
-     * @return the maximum gravity velocity in block
-     */
-    public double getGravityTerminalVelocity() {
-        return gravityTerminalVelocity;
-    }
-
     /**
      * Gets the number of tick this entity has been applied gravity.
      *
@@ -1008,13 +1010,11 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
      *
      * @param gravityDragPerTick      the gravity drag per tick in block
      * @param gravityAcceleration     the gravity acceleration in block
-     * @param gravityTerminalVelocity the gravity terminal velocity (maximum) in block
      * @see <a href="https://minecraft.gamepedia.com/Entity#Motion_of_entities">Entities motion</a>
      */
-    public void setGravity(double gravityDragPerTick, double gravityAcceleration, double gravityTerminalVelocity) {
+    public void setGravity(double gravityDragPerTick, double gravityAcceleration) {
         this.gravityDragPerTick = gravityDragPerTick;
         this.gravityAcceleration = gravityAcceleration;
-        this.gravityTerminalVelocity = gravityTerminalVelocity;
     }
 
     /**
@@ -1643,6 +1643,107 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
         tag.write(nbtCompound, value);
     }
 
+    /**
+     * Sets the Entity's {@link gravityAcceleration} and {@link gravityDragPerTick} fields to
+     * the default values according to <a href="https://minecraft.fandom.com/wiki/Entity#Motion_of_entities">Motion of entities</a>
+     */
+    @SuppressWarnings("JavadocReference")
+    private void initializeDefaultGravity() {
+        // TODO Add support for these values in the data generator
+        // Acceleration
+        switch (entityType) {
+            // 0
+            case ITEM_FRAME:
+                this.gravityAcceleration = 0;
+                break;
+            // 0.03
+            case EGG:
+            case FISHING_BOBBER:
+            case EXPERIENCE_BOTTLE:
+            case ENDER_PEARL:
+            case POTION:
+            case SNOWBALL:
+                this.gravityAcceleration = 0.03;
+                break;
+            // 0.04
+            case BOAT:
+            case TNT:
+            case FALLING_BLOCK:
+            case ITEM:
+            case MINECART:
+                this.gravityAcceleration = 0.04;
+                break;
+            // 0.05
+            case ARROW:
+            case SPECTRAL_ARROW:
+            case TRIDENT:
+                this.gravityAcceleration = 0.05;
+                break;
+            // 0.06
+            case LLAMA_SPIT:
+                this.gravityAcceleration = 0.06;
+                break;
+            // 0.1
+            case FIREBALL:
+            case WITHER_SKULL:
+            case DRAGON_FIREBALL:
+                this.gravityAcceleration = 0.1;
+                break;
+            // 0.08
+            default:
+                this.gravityAcceleration = 0.08;
+                break;
+        }
+
+        // Drag
+        switch (entityType) {
+            // 0
+            case BOAT:
+                this.gravityDragPerTick = 0;
+                break;
+            // 0.01
+            case LLAMA_SPIT:
+            case ENDER_PEARL:
+            case POTION:
+            case SNOWBALL:
+            case EGG:
+            case TRIDENT:
+            case SPECTRAL_ARROW:
+            case ARROW:
+                this.gravityDragPerTick = 0.01;
+                break;
+            // 0.05
+            case MINECART:
+                this.gravityDragPerTick = 0.05;
+                break;
+            // 0.08
+            case FISHING_BOBBER:
+                this.gravityDragPerTick = 0.08;
+                break;
+            // 0.02
+            default:
+                this.gravityDragPerTick = 0.02;
+                break;
+        }
+    }
+
+    /**
+     * Applies knockback to the entity
+     *
+     * @param strength the strength of the knockback, 0.4 is the vanilla value for a bare hand hit
+     * @param x knockback on x axle, for default knockback use the following formula <pre>sin(attacker.yaw * (pi/180))</pre>
+     * @param z knockback on z axle, for default knockback use the following formula <pre>-cos(attacker.yaw * (pi/180))</pre>
+     */
+    public void takeKnockback(final float strength, final double x, final double z) {
+        if (strength > 0) {
+            //TODO check possible side effects of unnatural TPS (other than 20TPS)
+            final Vector velocityModifier = new Vector(x, 0d, z).normalize().multiply(strength * MinecraftServer.TICK_PER_SECOND / 2);
+            this.velocity.setX(velocity.getX() / 2d - velocityModifier.getX());
+            this.velocity.setY(onGround ? Math.min(.4d, velocity.getY() / 2d + strength) * MinecraftServer.TICK_PER_SECOND : velocity.getY());
+            this.velocity.setZ(velocity.getZ() / 2d - velocityModifier.getZ());
+        }
+    }
+
     public enum Pose {
         STANDING,
         FALL_FLYING,

src/main/java/net/minestom/server/entity/EntityProjectile.java

@@ -47,7 +47,6 @@ public class EntityProjectile extends Entity {
         if (getEntityMeta() instanceof ProjectileMeta) {
             ((ProjectileMeta) getEntityMeta()).setShooter(this.shooter);
         }
-        setGravity(0.02f, 0.04f, 1.96f);
     }
 
     @Nullable

src/main/java/net/minestom/server/entity/ExperienceOrb.java

@@ -17,7 +17,6 @@ public class ExperienceOrb extends Entity {
 
     public ExperienceOrb(short experienceCount, @NotNull Position spawnPosition) {
         super(EntityType.EXPERIENCE_ORB, spawnPosition);
-        setGravity(0.02f, 0.04f, 1.96f);
         setBoundingBox(0.5f, 0.5f, 0.5f);
         //todo vanilla sets random velocity here?
         this.experienceCount = experienceCount;

src/main/java/net/minestom/server/entity/ItemEntity.java

@@ -43,7 +43,6 @@ public class ItemEntity extends Entity {
     public ItemEntity(@NotNull ItemStack itemStack, @NotNull Position spawnPosition) {
         super(EntityType.ITEM, spawnPosition);
         setItemStack(itemStack);
-        setGravity(0.02f, 0.04f, 1.96f);
         setBoundingBox(0.25f, 0.25f, 0.25f);
     }
 

src/main/java/net/minestom/server/entity/LivingEntity.java

@@ -90,7 +90,6 @@ public class LivingEntity extends Entity implements EquipmentHandler {
      */
     public LivingEntity(@NotNull EntityType entityType, @NotNull UUID uuid) {
         this(entityType, uuid, new Position());
-        setGravity(0.02f, 0.08f, 3.92f);
         initEquipments();
     }
 
@@ -104,7 +103,6 @@ public class LivingEntity extends Entity implements EquipmentHandler {
     @Deprecated
     public LivingEntity(@NotNull EntityType entityType, @NotNull UUID uuid, @NotNull Position spawnPosition) {
         super(entityType, uuid, spawnPosition);
-        setGravity(0.02f, 0.08f, 3.92f);
         initEquipments();
     }
 
@@ -781,4 +779,18 @@ public class LivingEntity extends Entity implements EquipmentHandler {
         return null;
     }
 
+    /**
+     * Applies knockback
+     * <p>
+     * Note: The strength is reduced based on knockback resistance
+     *
+     * @param strength the strength of the knockback, 0.4 is the vanilla value for a bare hand hit
+     * @param x knockback on x axle, for default knockback use the following formula <pre>sin(attacker.yaw * (pi/180))</pre>
+     * @param z knockback on z axle, for default knockback use the following formula <pre>-cos(attacker.yaw * (pi/180))</pre>
+     */
+    @Override
+    public void takeKnockback(float strength, final double x, final double z) {
+        strength *= 1 - getAttributeValue(Attribute.KNOCKBACK_RESISTANCE);
+        super.takeKnockback(strength, x, z);
+    }
 }

src/test/java/demo/PlayerInit.java

@@ -50,16 +50,12 @@ public class PlayerInit {
             .addListener(EntityAttackEvent.class, event -> {
                 final Entity source = event.getEntity();
                 final Entity entity = event.getTarget();
+
+                entity.takeKnockback(0.4f, Math.sin(source.getPosition().getYaw() * 0.017453292), -Math.cos(source.getPosition().getYaw() * 0.017453292));
+
                 if (entity instanceof Player) {
                     Player target = (Player) entity;
-                    Vector velocity = source.getPosition().clone().getDirection().multiply(4);
-                    velocity.setY(3.5f);
-                    target.setVelocity(velocity);
                     target.damage(DamageType.fromEntity(source), 5);
-                } else {
-                    Vector velocity = source.getPosition().clone().getDirection().multiply(3);
-                    velocity.setY(3f);
-                    entity.setVelocity(velocity);
                 }
 
                 if (source instanceof Player) {