fix: transposed heightmap restore left resumed chunks with stone surfaces (#2448)

pumpkin-world/src/generation/proto_chunk.rs

@@ -295,7 +295,7 @@ impl ProtoChunk {
 
         for z in 0..16 {
             for x in 0..16 {
-                let index = ((z << 4) + x) as usize;
+                let index = Self::local_position_to_height_map_index(x, z);
 
                 proto_chunk.flat_motion_blocking_height_map[index] = heightmap_data.get(
                     ChunkHeightmapType::MotionBlocking,

pumpkin-world/src/generation/proto_chunk_test.rs

@@ -5,6 +5,93 @@ mod test {
     use pumpkin_data::dimension::Dimension;
     use pumpkin_util::world_seed::Seed;
 
+    // Regression test for transposed heightmaps during Noise-stage chunk resume.
+    // Flat terrain cannot expose this bug, so use a sloped chunk.
+    #[test]
+    fn heightmap_roundtrip_through_chunk_data_resume() {
+        use crate::chunk_system::chunk_state::Chunk;
+        use pumpkin_config::lighting::LightingEngineConfig;
+        use pumpkin_util::math::vector3::Vector3;
+
+        let seed = Seed(1779920288596261407);
+        let (cx, cz) = (67i32, 63i32);
+        let world_gen = get_world_gen(seed, Dimension::OVERWORLD, false, Vec::new(), String::new());
+        let WorldGenerator::Noise(generator) = &*world_gen else {
+            unreachable!()
+        };
+
+        let mut proto = ProtoChunk::new(cx, cz, &world_gen);
+        proto.step_to_biomes(generator);
+        proto.set_structure_starts(generator);
+        proto.set_structure_references(generator);
+        proto.step_to_noise(generator);
+
+        let mut expected_heights = [[0i32; 16]; 16];
+        for z in 0..16i32 {
+            for x in 0..16i32 {
+                expected_heights[z as usize][x as usize] = proto.top_block_height_exclusive(x, z);
+            }
+        }
+
+        let mut staged = Chunk::Proto(Box::new(proto));
+        staged.upgrade_to_level_chunk(&Dimension::OVERWORLD, &LightingEngineConfig::Default);
+        let Chunk::Level(chunk_data) = staged else {
+            unreachable!()
+        };
+        assert_eq!(chunk_data.status, pumpkin_data::chunk::ChunkStatus::Noise);
+
+        let mut resumed = ProtoChunk::from_chunk_data(&chunk_data, &world_gen);
+        assert_eq!(resumed.stage, StagedChunkEnum::Noise);
+
+        let mut height_mismatches = 0;
+        for z in 0..16i32 {
+            for x in 0..16i32 {
+                let expected = expected_heights[z as usize][x as usize];
+                let got = resumed.top_block_height_exclusive(x, z);
+                if got != expected {
+                    height_mismatches += 1;
+                }
+            }
+        }
+        assert_eq!(
+            height_mismatches, 0,
+            "heightmap corrupted by save/load roundtrip (transposed or lost)"
+        );
+
+        resumed.step_to_surface(generator);
+
+        let mut fresh = ProtoChunk::new(cx, cz, &world_gen);
+        fresh.step_to_biomes(generator);
+        fresh.set_structure_starts(generator);
+        fresh.set_structure_references(generator);
+        fresh.step_to_noise(generator);
+        fresh.step_to_surface(generator);
+
+        let bottom = fresh.bottom_y() as i32;
+        let top = bottom + fresh.height() as i32;
+        let mut surface_mismatches = 0;
+        for lz in 0..16i32 {
+            for lx in 0..16i32 {
+                let (wx, wz) = (cx * 16 + lx, cz * 16 + lz);
+                for y in (bottom..top).rev() {
+                    let f = fresh.get_block_state(&Vector3::new(wx, y, wz)).to_state();
+                    if f.is_air() || f.is_liquid() {
+                        continue;
+                    }
+                    let r = resumed.get_block_state(&Vector3::new(wx, y, wz)).to_state();
+                    if f.id != r.id {
+                        surface_mismatches += 1;
+                    }
+                    break;
+                }
+            }
+        }
+        assert_eq!(
+            surface_mismatches, 0,
+            "resumed chunk surface differs from uninterrupted generation (stone-trail bug)"
+        );
+    }
+
     #[test]
     fn no_blend_no_beard_0_0() {
         let seed = Seed(0);