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Paper/patches/server/1023-Remove-wall-time-unused-skip-tick-protection.patch
Bjarne Koll d0dcd7d251
Fix incorrect invulnerability damage reduction (#11599) 
Fixes incorrect spigot handling of the invulnerability damage
reduction applied when an already invulnerable entity is damaged with a
larger damage amount than the initial damage.
Vanilla still damages entities even if invulnerable if the damage to be
applied is larger than the previous damage taken. In that case, vanilla
applies the difference between the previous damage taken and the
proposed damage.

Spigot's damage modifier API takes over the computation of damage
reducing effects, however spigot invokes this handling with the initial
damage before computing the difference to the previous damage amount.
This leads to the reduction values to generally be larger than expected,
as they are computed on the not-yet-reduced value.
Spigot applies these reductions after calling the EntityDamageEvent and
*then* subtracts the previous damage point, leading to the final damage
amount being smaller than expected.

This patch cannot simply call the EntityDamageEvent with the reduced
damage, as that would lead to EntityDamageEvent#getDamage() returning
the already reduced damage, which breaks its method contract.
Instead, this patch makes use of the DamageModifier API, implementing
the last-damage-reduction as a DamageModifier.
2024-11-19 11:54:58 +01:00

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Bjarne Koll <git@lynxplay.dev>
Date: Mon, 16 Sep 2024 23:07:29 +0200
Subject: [PATCH] Remove wall-time / unused skip tick protection
Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.
To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.
These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.
Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.
diff --git a/src/main/java/net/minecraft/world/entity/item/ItemEntity.java b/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
index 4ce041726661dbbd19f36a516f2fd7f5e3307ef0..0f086af57a5ff08c264dcbf89a8c3931ec73a609 100644
--- a/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
+++ b/src/main/java/net/minecraft/world/entity/item/ItemEntity.java
@@ -60,7 +60,7 @@ public class ItemEntity extends Entity implements TraceableEntity {
@Nullable
public UUID target;
public final float bobOffs;
- private int lastTick = MinecraftServer.currentTick - 1; // CraftBukkit
+ // private int lastTick = MinecraftServer.currentTick - 1; // CraftBukkit // Paper - remove anti tick skipping measures / wall time
public boolean canMobPickup = true; // Paper - Item#canEntityPickup
private int despawnRate = -1; // Paper - Alternative item-despawn-rate
public net.kyori.adventure.util.TriState frictionState = net.kyori.adventure.util.TriState.NOT_SET; // Paper - Friction API
@@ -153,12 +153,11 @@ public class ItemEntity extends Entity implements TraceableEntity {
this.discard(EntityRemoveEvent.Cause.DESPAWN); // CraftBukkit - add Bukkit remove cause
} else {
super.tick();
- // CraftBukkit start - Use wall time for pickup and despawn timers
- int elapsedTicks = MinecraftServer.currentTick - this.lastTick;
- if (this.pickupDelay != 32767) this.pickupDelay -= elapsedTicks;
- if (this.age != -32768) this.age += elapsedTicks;
- this.lastTick = MinecraftServer.currentTick;
- // CraftBukkit end
+ // Paper start - remove anti tick skipping measures / wall time - revert to vanilla
+ if (this.pickupDelay > 0 && this.pickupDelay != 32767) {
+ --this.pickupDelay;
+ }
+ // Paper end - remove anti tick skipping measures / wall time - revert to vanilla
this.xo = this.getX();
this.yo = this.getY();
@@ -212,7 +211,7 @@ public class ItemEntity extends Entity implements TraceableEntity {
this.mergeWithNeighbours();
}
- /* CraftBukkit start - moved up
+ // Paper - remove anti tick skipping measures / wall time - revert to vanilla /* CraftBukkit start - moved up
if (this.age != -32768) {
++this.age;
}
@@ -243,12 +242,14 @@ public class ItemEntity extends Entity implements TraceableEntity {
// Spigot start - copied from above
@Override
public void inactiveTick() {
- // CraftBukkit start - Use wall time for pickup and despawn timers
- int elapsedTicks = MinecraftServer.currentTick - this.lastTick;
- if (this.pickupDelay != 32767) this.pickupDelay -= elapsedTicks;
- if (this.age != -32768) this.age += elapsedTicks;
- this.lastTick = MinecraftServer.currentTick;
- // CraftBukkit end
+ // Paper start - remove anti tick skipping measures / wall time - copied from above
+ if (this.pickupDelay > 0 && this.pickupDelay != 32767) {
+ --this.pickupDelay;
+ }
+ if (this.age != -32768) {
+ ++this.age;
+ }
+ // Paper end - remove anti tick skipping measures / wall time - copied from above
if (!this.level().isClientSide && this.age >= this.despawnRate) { // Spigot // Paper - Alternative item-despawn-rate
// CraftBukkit start - fire ItemDespawnEvent
diff --git a/src/main/java/net/minecraft/world/entity/monster/Zombie.java b/src/main/java/net/minecraft/world/entity/monster/Zombie.java
index 94b3ba2688676e92d9d093b63d92cab39d5d2f02..a12461907278cfbfa3b1c0aa74b9f07a31768b8a 100644
--- a/src/main/java/net/minecraft/world/entity/monster/Zombie.java
+++ b/src/main/java/net/minecraft/world/entity/monster/Zombie.java
@@ -98,7 +98,7 @@ public class Zombie extends Monster {
private boolean canBreakDoors;
private int inWaterTime;
public int conversionTime;
- private int lastTick = MinecraftServer.currentTick; // CraftBukkit - add field
+ // private int lastTick = MinecraftServer.currentTick; // CraftBukkit - add field // Paper - remove anti tick skipping measures / wall time
private boolean shouldBurnInDay = true; // Paper - Add more Zombie API
public Zombie(EntityType<? extends Zombie> type, Level world) {
@@ -217,10 +217,7 @@ public class Zombie extends Monster {
public void tick() {
if (!this.level().isClientSide && this.isAlive() && !this.isNoAi()) {
if (this.isUnderWaterConverting()) {
- // CraftBukkit start - Use wall time instead of ticks for conversion
- int elapsedTicks = MinecraftServer.currentTick - this.lastTick;
- this.conversionTime -= elapsedTicks;
- // CraftBukkit end
+ --this.conversionTime; // Paper - remove anti tick skipping measures / wall time
if (this.conversionTime < 0) {
this.doUnderWaterConversion();
}
@@ -237,7 +234,7 @@ public class Zombie extends Monster {
}
super.tick();
- this.lastTick = MinecraftServer.currentTick; // CraftBukkit
+ // this.lastTick = MinecraftServer.currentTick; // CraftBukkit // Paper - remove anti tick skipping measures / wall time
}
@Override
@@ -278,7 +275,7 @@ public class Zombie extends Monster {
}
// Paper end - Add more Zombie API
public void startUnderWaterConversion(int ticksUntilWaterConversion) {
- this.lastTick = MinecraftServer.currentTick; // CraftBukkit
+ // this.lastTick = MinecraftServer.currentTick; // CraftBukkit // Paper - remove anti tick skipping measures / wall time
this.conversionTime = ticksUntilWaterConversion;
this.getEntityData().set(Zombie.DATA_DROWNED_CONVERSION_ID, true);
}
diff --git a/src/main/java/net/minecraft/world/level/block/entity/BrewingStandBlockEntity.java b/src/main/java/net/minecraft/world/level/block/entity/BrewingStandBlockEntity.java
index 2bafacd7bc56186d9105d2031180f8c4a6940018..4ea29e8f2b39d7b44e0461d6a2cdd3fc257abd44 100644
--- a/src/main/java/net/minecraft/world/level/block/entity/BrewingStandBlockEntity.java
+++ b/src/main/java/net/minecraft/world/level/block/entity/BrewingStandBlockEntity.java
@@ -55,7 +55,7 @@ public class BrewingStandBlockEntity extends BaseContainerBlockEntity implements
public int fuel;
protected final ContainerData dataAccess;
// CraftBukkit start - add fields and methods
- private int lastTick = MinecraftServer.currentTick;
+ // private int lastTick = MinecraftServer.currentTick; // Paper - remove anti tick skipping measures / wall time
public List<HumanEntity> transaction = new java.util.ArrayList<HumanEntity>();
private int maxStack = MAX_STACK;
@@ -170,12 +170,10 @@ public class BrewingStandBlockEntity extends BaseContainerBlockEntity implements
boolean flag1 = blockEntity.brewTime > 0;
ItemStack itemstack1 = (ItemStack) blockEntity.items.get(3);
- // CraftBukkit start - Use wall time instead of ticks for brewing
- int elapsedTicks = MinecraftServer.currentTick - blockEntity.lastTick;
- blockEntity.lastTick = MinecraftServer.currentTick;
+ // Paper - remove anti tick skipping measures / wall time
if (flag1) {
- blockEntity.brewTime -= elapsedTicks;
+ --blockEntity.brewTime; // Paper - remove anti tick skipping measures / wall time - revert to vanilla
boolean flag2 = blockEntity.brewTime <= 0; // == -> <=
// CraftBukkit end
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