From a8e767250a3df17983367830982311e13857e6e2 Mon Sep 17 00:00:00 2001
From: Nassim Jahnke <jahnke.nassim@gmail.com>
Date: Sat, 22 Jan 2022 11:52:09 +0100
Subject: [PATCH] Fix 1.17->1.16 heightmap conversion Fixes
 ViaVersion/ViaVersion#2801

---
 .../packets/BlockItemPackets1_17.java             | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java b/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
index 5d78ab2b..17fafebf 100644
--- a/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
+++ b/common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_16_4to1_17/packets/BlockItemPackets1_17.java
@@ -30,6 +30,9 @@ import com.viaversion.viaversion.api.minecraft.chunks.ChunkSection;
 import com.viaversion.viaversion.api.protocol.packet.PacketWrapper;
 import com.viaversion.viaversion.api.protocol.remapper.PacketRemapper;
 import com.viaversion.viaversion.api.type.Type;
+import com.viaversion.viaversion.libs.opennbt.tag.builtin.CompoundTag;
+import com.viaversion.viaversion.libs.opennbt.tag.builtin.LongArrayTag;
+import com.viaversion.viaversion.libs.opennbt.tag.builtin.Tag;
 import com.viaversion.viaversion.protocols.protocol1_16_2to1_16_1.ClientboundPackets1_16_2;
 import com.viaversion.viaversion.protocols.protocol1_16_2to1_16_1.ServerboundPackets1_16_2;
 import com.viaversion.viaversion.protocols.protocol1_16_2to1_16_1.types.Chunk1_16_2Type;
@@ -38,6 +41,8 @@ import com.viaversion.viaversion.protocols.protocol1_17to1_16_4.ClientboundPacke
 import com.viaversion.viaversion.protocols.protocol1_17to1_16_4.ServerboundPackets1_17;
 import com.viaversion.viaversion.protocols.protocol1_17to1_16_4.types.Chunk1_17Type;
 import com.viaversion.viaversion.rewriter.BlockRewriter;
+import com.viaversion.viaversion.util.CompactArrayUtil;
+import com.viaversion.viaversion.util.MathUtil;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -282,6 +287,16 @@ public final class BlockItemPackets1_17 extends ItemRewriter<Protocol1_16_4To1_1
                     ChunkSection[] sections = Arrays.copyOfRange(chunk.getSections(), startFromSection, startFromSection + 16);
                     chunk.setSections(sections);
 
+                    CompoundTag heightMaps = chunk.getHeightMap();
+                    for (Tag heightMapTag : heightMaps.values()) {
+                        LongArrayTag heightMap = (LongArrayTag) heightMapTag;
+                        int[] heightMapData = new int[256];
+                        int bitsPerEntry = MathUtil.ceilLog2((currentWorldSectionHeight << 4) + 1);
+                        // Shift back to 0 based and clamp to normal height with 9 bits
+                        CompactArrayUtil.iterateCompactArrayWithPadding(bitsPerEntry, heightMapData.length, heightMap.getValue(), (i, v) -> heightMapData[i] = MathUtil.clamp(v + tracker.currentMinY(), 0, 255));
+                        heightMap.setValue(CompactArrayUtil.createCompactArrayWithPadding(9, heightMapData.length, i -> heightMapData[i]));
+                    }
+
                     for (int i = 0; i < 16; i++) {
                         ChunkSection section = sections[i];
                         if (section == null) continue;