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 a3fc76b512244ed6ca6b4d8f4babcb81f3cce226..90ba51e05bbed0366b43bc9315f6dfa9e39eee03 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -543,4 +543,9 @@ public class PaperWorldConfig {
         }
         log("Anti-Xray: " + (antiXray ? "enabled" : "disabled") + " / Engine Mode: " + engineMode.getDescription() + " / Up to " + ((maxChunkSectionIndex + 1) * 16) + " blocks / Update Radius: " + updateRadius);
     }
+
+    public boolean disableRelativeProjectileVelocity;
+    private void disableRelativeProjectileVelocity() {
+        disableRelativeProjectileVelocity = getBoolean("game-mechanics.disable-relative-projectile-velocity", false);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/EntityArrow.java b/src/main/java/net/minecraft/server/EntityArrow.java
index 634e2bd3049d65bbef4ef12e2264049a6980fd71..9c97edf9c9e9a8cdf029264f6b563090142c686b 100644
--- a/src/main/java/net/minecraft/server/EntityArrow.java
+++ b/src/main/java/net/minecraft/server/EntityArrow.java
@@ -85,7 +85,7 @@ public abstract class EntityArrow extends Entity implements IProjectile {
         float f7 = MathHelper.cos(f1 * 0.017453292F) * MathHelper.cos(f * 0.017453292F);
 
         this.shoot((double) f5, (double) f6, (double) f7, f3, f4);
-        this.setMot(this.getMot().add(entity.getMot().x, entity.onGround ? 0.0D : entity.getMot().y, entity.getMot().z));
+        if (!entity.world.paperConfig.disableRelativeProjectileVelocity) this.setMot(this.getMot().add(entity.getMot().x, entity.onGround ? 0.0D : entity.getMot().y, entity.getMot().z)); // Paper - allow disabling relative velocity
     }
 
     @Override
diff --git a/src/main/java/net/minecraft/server/EntityProjectile.java b/src/main/java/net/minecraft/server/EntityProjectile.java
index 6c091b68087d60b0b916871eb0ce06c6a2776bf8..f5c8074dcf1c6275bc13eb8f2b67c04ca547877b 100644
--- a/src/main/java/net/minecraft/server/EntityProjectile.java
+++ b/src/main/java/net/minecraft/server/EntityProjectile.java
@@ -43,7 +43,7 @@ public abstract class EntityProjectile extends Entity implements IProjectile {
         this.shoot((double) f5, (double) f6, (double) f7, f3, f4);
         Vec3D vec3d = entity.getMot();
 
-        this.setMot(this.getMot().add(vec3d.x, entity.onGround ? 0.0D : vec3d.y, vec3d.z));
+        if (!entity.world.paperConfig.disableRelativeProjectileVelocity) this.setMot(this.getMot().add(vec3d.x, entity.onGround ? 0.0D : vec3d.y, vec3d.z)); // Paper - allow disabling relative velocity
     }
 
     @Override
