#1406: Fix incorrect assumption of Fireball having constant speed

By: DerFrZocker <derrieple@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftFireball.java

@@ -6,6 +6,7 @@ import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.entity.Fireball;
 import org.bukkit.projectiles.ProjectileSource;
 import org.bukkit.util.Vector;
+import org.jetbrains.annotations.NotNull;
 
 public class CraftFireball extends AbstractProjectile implements Fireball {
     public CraftFireball(CraftServer server, EntityFireball entity) {
@@ -49,7 +50,7 @@ public class CraftFireball extends AbstractProjectile implements Fireball {
 
     @Override
     public Vector getDirection() {
-        return new Vector(getHandle().xPower, getHandle().yPower, getHandle().zPower);
+        return getAcceleration();
     }
 
     @Override
@@ -57,23 +58,32 @@ public class CraftFireball extends AbstractProjectile implements Fireball {
         Preconditions.checkArgument(direction != null, "Vector direction cannot be null");
         if (direction.isZero()) {
             setVelocity(direction);
+            setAcceleration(direction);
             return;
         }
-        getHandle().assignPower(direction.getX(), direction.getY(), direction.getZ());
+
-        update(); // SPIGOT-6579
+        direction = direction.clone().normalize();
+        setVelocity(direction.clone().multiply(getVelocity().length()));
+        setAcceleration(direction.multiply(getAcceleration().length()));
     }
 
     @Override
-    public void setVelocity(Vector velocity) {
+    public void setAcceleration(@NotNull Vector acceleration) {
-        Preconditions.checkArgument(velocity != null, "Vector velocity cannot be null");
+        Preconditions.checkArgument(acceleration != null, "Vector acceleration cannot be null");
-        // SPIGOT-6993: Allow power to be higher / lower than the normalized direction enforced by #setDirection(Vector)
+        // SPIGOT-6993: EntityFireball#assignPower will normalize the given values
-        // Note: Because of MC-80142 the fireball will stutter on the client when setting the velocity to something other than 0 or the normalized vector * 0.1
+        // Note: Because of MC-80142 the fireball will stutter on the client when setting the power to something other than 0 or the normalized vector * 0.1
-        getHandle().xPower = velocity.getX();
+        getHandle().xPower = acceleration.getX();
-        getHandle().yPower = velocity.getY();
+        getHandle().yPower = acceleration.getY();
-        getHandle().zPower = velocity.getZ();
+        getHandle().zPower = acceleration.getZ();
         update(); // SPIGOT-6579
     }
 
+    @NotNull
+    @Override
+    public Vector getAcceleration() {
+        return new Vector(getHandle().xPower, getHandle().yPower, getHandle().zPower);
+    }
+
     @Override
     public EntityFireball getHandle() {
         return (EntityFireball) entity;