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 f2a5426934e712c828cf0369058ff2fb5353075e..ab2ddb39b0d15a5c40101f957fcd4c8d7a588c87 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -501,4 +501,9 @@ 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/server/IProjectile.java b/src/main/java/net/minecraft/server/IProjectile.java
index 8d26521bc414b3d34f496e966f0c918b023f4833..9f5ce64a60fe7c312399ee416b11b84213dd3bee 100644
--- a/src/main/java/net/minecraft/server/IProjectile.java
+++ b/src/main/java/net/minecraft/server/IProjectile.java
@@ -114,7 +114,7 @@ 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) {