From 7c4da0c8a17327ae7a0232a4e61a7643a10e1ef8 Mon Sep 17 00:00:00 2001
From: EtlamGit <etlam@nurfuerspam.de>
Date: Wed, 8 Jan 2025 18:41:56 +0100
Subject: [PATCH] fix skipped section when all blocks are identical

this condition was wrongly detected as "everything is air", resulting in skipping this section
---
 chunk.cpp | 24 ++++++++++++++++++------
 chunk.h   | 10 +++++-----
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/chunk.cpp b/chunk.cpp
index dc778a3..da7804f 100755
--- a/chunk.cpp
+++ b/chunk.cpp
@@ -50,6 +50,9 @@ Chunk::~Chunk() {
   }
 }
 
+const unsigned int Chunk::air_hid = qHash(QString("minecraft:air"));
+
+
 void Chunk::findHighestBlock()
 {
   // loop over all Sections in reverse order
@@ -59,7 +62,10 @@ void Chunk::findHighestBlock()
     it.previous();
     if (it.value()) {
       for (int j = 4095; j >= 0; j--) {
-        if (it.value()->blocks[j]) {
+        const ChunkSection* cs = it.value();
+        auto blockid = cs->blocks[j];
+        auto hid     = cs->blockPalette[blockid].hid;
+        if (hid != air_hid) {
           // found first non-air Block
           highest = it.key() * 16 + (j >> 8);
           return;
@@ -494,8 +500,11 @@ bool Chunk::loadSection1519(ChunkSection *cs, const Tag *section) {
     loadSection_loadBlockStates(cs, section->at("BlockStates"));
     sectionContainsData = true;
   } else {
-    // set everything to 0 (minecraft:air)
+    // data tag is missing -> invent empty data
     memset(cs->blocks, 0, sizeof(cs->blocks));
+    if ((cs->blockPaletteLength > 0) && (cs->blockPalette[0].name != "minecraft:air" )) {
+      sectionContainsData = true;
+    }
   }
 
   // copy Light data
@@ -527,16 +536,18 @@ bool Chunk::loadSection2844(ChunkSection * cs, const Tag * section) {
     loadSection_loadBlockStates(cs, section->at("block_states")->at("data"));
     sectionContainsData = true;
   } else {
-    // set everything to 0 (minecraft:air)
+    // data tag is missing -> invent empty data
     memset(cs->blocks, 0, sizeof(cs->blocks));
+    if ((cs->blockPaletteLength > 0) && (cs->blockPalette[0].name != "minecraft:air" )) {
+      sectionContainsData = true;
+    }
   }
 
   // decode Biomes-Palette to be able to map Biome
   if (section->has("biomes") && section->at("biomes")->has("palette")) {
     loadSection_decodeBiomePalette(cs, section->at("biomes"));
-    sectionContainsData = true;
   } else {
-    // never observed in real live
+    // observed for unused Y == 20 section
     // probably we should create some default Biome in this case
     sectionContainsData = false;
   }
@@ -605,7 +616,8 @@ void Chunk::loadSection_createDummyPalette(ChunkSection *cs) {
   // create a dummy palette
   cs->blockPalette = new PaletteEntry[1];
   cs->blockPalette[0].name = "minecraft:air";
-  cs->blockPalette[0].hid  = 0;
+  cs->blockPalette[0].hid  = air_hid;
+  cs->blockPaletteLength = 1;
 }
 
 
diff --git a/chunk.h b/chunk.h
index 57aab1c..3d2a760 100644
--- a/chunk.h
+++ b/chunk.h
@@ -97,12 +97,12 @@ class Chunk : public QObject {
   short  depth[16 * 16];      // cached depth map to create shadow
   EntityMap entities;
 
-  /** Specifies whether the chunk is locked by the ChunkLock resourcepack. */
-  bool isChunkLocked;
+  // ChunkLocked feature:
+  bool    isChunkLocked;      // flag specifies whether the chunk is locked by the ChunkLock resourcepack
+  QString chunkLockItemName;  // the name of the item needed for unlocking the chunk
 
-  /** The name of the item needed for unlocking the chunk.
-  Only valid if isChunkLocked is true. */
-  QString chunkLockItemName;
+  // HID used for minecraft:air
+  static const unsigned int air_hid;
 
   friend class MapView;
   friend class ChunkRenderer;