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 384cb363eed794551bee6b0ec11ba1be92a3d7ac..1ee2cced100626e48eb36ee14f84b9257c79a2f8 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -507,4 +507,9 @@ public class PaperWorldConfig {
             Bukkit.getLogger().warning("You have enabled permission-based Anti-Xray checking - depending on your permission plugin, this may cause performance issues");
         }
     }
+
+    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/IProjectile.java b/src/main/java/net/minecraft/world/entity/projectile/IProjectile.java
index 1ff55a1b6c1faae95a83cd8fc12a2045ad479145..0e3c646dca1fa1fa895c3aece037367a9b2cf378 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/IProjectile.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/IProjectile.java
@@ -125,7 +125,7 @@ public abstract class IProjectile extends Entity {
         this.shoot((double) f5, (double) f6, (double) f7, f3, f4);
         Vec3D vec3d = entity.getMot();
 
-        this.setMot(this.getMot().add(vec3d.x, entity.isOnGround() ? 0.0D : vec3d.y, vec3d.z));
+        if (!entity.world.paperConfig.disableRelativeProjectileVelocity) this.setMot(this.getMot().add(vec3d.x, entity.isOnGround() ? 0.0D : vec3d.y, vec3d.z)); // Paper - allow disabling relative velocity
     }
 
     protected void a(MovingObjectPosition movingobjectposition) {