From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Lucavon <lucavonlp@gmail.com>
Date: Tue, 23 Jul 2019 20:29:20 -0500
Subject: [PATCH] Configurable projectile relative velocity

This patch adds an option "disable relative projectile velocity", which, when
nabled, will cause projectiles to ignore the shooter's current velocity,
like they did in Minecraft 1.8 and prior.
If a player is falling, for example, their shooting range will be drastically
reduced, as a downwards velocity is applied to the projectile. This prevents
players from saving themselves from falling off floating islands, for example,
as a thrown ender pearl will not make it back to the island, while it would
have in 1.8.

While this could easily be done with plugins, too, there are multiple problems:
P1) If multiple plugins cancel the velocity by subtracting the shooter's velocity
from the projectile's velocity, the projectile's velocity would be different.
As there's no way to detect whether the projectile's velocity has already been
adjusted to ignore the player's velocity, plugins can't not do it if it's not
necessary.
P2) I've noticed some inconsistencies, e.g. weird velocity when shooting while
using an elytra. Checking for those inconsistencies is possible, but not as
efficient as just not applying the velocity in the first place.
P3) Solutions for 1) and especially 2) might not be future-proof, while this
server-internal fix makes this change future-proof.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 9d52060319e6a0403c9979766c761e2f5324f6aa..de1820a6b0e568bbc13eea7a31e5cd40234c0f66 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -416,5 +416,10 @@ public class PaperWorldConfig {
             log("Using improved mob spawn limits (Only Natural Spawns impact spawn limits for more natural spawns)");
         }
     }
+
+    public boolean disableRelativeProjectileVelocity;
+    private void disableRelativeProjectileVelocity() {
+        disableRelativeProjectileVelocity = getBoolean("game-mechanics.disable-relative-projectile-velocity", false);
+    }
 }
 
diff --git a/src/main/java/net/minecraft/world/entity/projectile/Projectile.java b/src/main/java/net/minecraft/world/entity/projectile/Projectile.java
index 21ce4be0d8d0147a92f87e17bb5078a211419984..37356b36f0ae12d55150f399318581fa77c30cee 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/Projectile.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/Projectile.java
@@ -161,7 +161,7 @@ public abstract class Projectile extends Entity {
         this.shoot((double) f5, (double) f6, (double) f7, modifierZ, modifierXYZ);
         Vec3 vec3d = user.getDeltaMovement();
 
-        this.setDeltaMovement(this.getDeltaMovement().add(vec3d.x, user.isOnGround() ? 0.0D : vec3d.y, vec3d.z));
+        if (!user.level.paperConfig.disableRelativeProjectileVelocity) this.setDeltaMovement(this.getDeltaMovement().add(vec3d.x, user.isOnGround() ? 0.0D : vec3d.y, vec3d.z)); // Paper - allow disabling relative velocity
     }
 
     // CraftBukkit start - call projectile hit event