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93 lines
5.4 KiB
Diff
93 lines
5.4 KiB
Diff
From 82c64be280dc34840de9c10a2f4260cad8e8e690 Mon Sep 17 00:00:00 2001
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From: Zach Brown <zach.brown@destroystokyo.com>
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Date: Tue, 4 Sep 2018 19:07:57 -0400
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Subject: [PATCH] MC-2025: Save and load entity AABB to prevent wobble
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What follows is a summarized analysis provided on the Mojira and associated subreddit by various MC community members
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who have investigated this issue and found a solution. This work is largely a result of their efforts.
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The underlying cause of MC-2025 is that sometimes an AABB ends up slightly smaller than the desired width. If this
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happens before the entity is pushed up against a boundary (i.e. blocks or walls), then upon chunk save and reload, the
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AABB size will be recomputed such that it is intersecting the wall, allowing the entity to be pushed into the wall,
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suffocate, and die. Although the rounding artifacts get larger at larger world coordinates, the drift we see is
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miniscule. Closer to the world origin, we have seen error on the order of 2-46. Compare this to the fact that
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(due to MC-4), entity coordinates send to clients are quantized to multiples of 1/4096 (2-12).
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But, OMG, do the rounding errors mean that AABB's accumulate shrinkage over time? Actually, no. The statistics on IEEE
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rounding do not have that kind of bias. What has not been stated is that the AABB is just as likely to end up larger
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than the expected width; on save and reload, the entity ends up slightly away from the wall, and we don't notice any
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problem. In reality, the AABB size ends up undergoing random wobble around the expected value all the time, and that
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wobble isn't functionally any different from the kind we'd get even if we tried to force the AABB size to be stable!
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This reasoning leads us to one clear conclusion: The simplest, least invasive, and most correct solution is to just
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store the AABB in NBT data on chunk save and restore the AABB exactly as it was saved upon reload.
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diff --git a/src/main/java/net/minecraft/server/AxisAlignedBB.java b/src/main/java/net/minecraft/server/AxisAlignedBB.java
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index 92edfe0295..624f0e3956 100644
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--- a/src/main/java/net/minecraft/server/AxisAlignedBB.java
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+++ b/src/main/java/net/minecraft/server/AxisAlignedBB.java
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@@ -3,12 +3,12 @@ package net.minecraft.server;
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import javax.annotation.Nullable;
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public class AxisAlignedBB {
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- public final double a;
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- public final double b;
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- public final double c;
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- public final double d;
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- public final double e;
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- public final double f;
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+ public final double a; public double getMinX() { return this.a; } // Paper - OBFHELPER
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+ public final double b; public double getMinY() { return this.b; } // Paper - OBFHELPER
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+ public final double c; public double getMinZ() { return this.c; } // Paper - OBFHELPER
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+ public final double d; public double getMaxX() { return this.d; } // Paper - OBFHELPER
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+ public final double e; public double getMaxY() { return this.e; } // Paper - OBFHELPER
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+ public final double f; public double getMaxZ() { return this.f; } // Paper - OBFHELPER
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public AxisAlignedBB(double d0, double d1, double d2, double d3, double d4, double d5) {
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this.a = Math.min(d0, d3);
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diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
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index 2b1affd03c..1fae9aa074 100644
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--- a/src/main/java/net/minecraft/server/Entity.java
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+++ b/src/main/java/net/minecraft/server/Entity.java
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@@ -1658,6 +1658,12 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
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if (spawnedViaMobSpawner) {
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nbttagcompound.setBoolean("Paper.FromMobSpawner", true);
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}
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+ // Paper start - MC-2025 fix - Save entity AABB and load it, floating point issues recalculating AABB can result in wobble
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+ AxisAlignedBB boundingBox = this.getBoundingBox();
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+ nbttagcompound.set("Paper.AAAB", this.createList(
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+ boundingBox.getMinX(), boundingBox.getMinY(), boundingBox.getMinZ(),
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+ boundingBox.getMaxX(), boundingBox.getMaxY(), boundingBox.getMaxZ()
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+ ));
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// Paper end
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return nbttagcompound;
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} catch (Throwable throwable) {
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@@ -1747,6 +1753,16 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
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if (this.aD()) {
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this.setPosition(this.locX, this.locY, this.locZ);
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}
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+ // Paper start - MC-2025 fix - Save entity AABB and load it, floating point issues recalculating AABB can result in wobble
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+ // Placement is important, always after the setPosition call above
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+ if (nbttagcompound.hasKey("Paper.AABB")) {
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+ NBTTagList savedBB = nbttagcompound.getList("Paper.AABB", 6);
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+ this.setBoundingBox(new AxisAlignedBB(
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+ savedBB.getDoubleAt(0), savedBB.getDoubleAt(1), savedBB.getDoubleAt(2),
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+ savedBB.getDoubleAt(3), savedBB.getDoubleAt(4), savedBB.getDoubleAt(5)
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+ ));
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+ }
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+ // Paper end
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// CraftBukkit start
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if (this instanceof EntityLiving) {
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@@ -2815,6 +2831,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
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return this.boundingBox;
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}
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+ public void setBoundingBox(AxisAlignedBB axisAlignedBB) { this.a(axisAlignedBB); } // Paper - OBFHELPER
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public void a(AxisAlignedBB axisalignedbb) {
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// CraftBukkit start - block invalid bounding boxes
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double a = axisalignedbb.a,
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--
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2.18.0
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