Map Star Fissures to modern world minimum Y (#58)

docs/WRITING_GRAMMAR.md

@@ -20,6 +20,6 @@ Material pages are generated for registered full-collision, non-fluid blocks and
 
 Crystal Formations are an authored, material-free feature on exposed solid terrain, including Flat terrain; Cave and Void reject the page. Like Legacy, one in fifteen eligible chunks attempts a formation, with the site fixed by the Age seed and chunk coordinates. The modern formation is a compact mound with budding hearts instead of Legacy's long crystal lines. Budding blocks grow through small, medium, and large buds into clusters using vanilla amethyst timing and sounds. Non-silk cluster harvest yields Crystal Shards; four shards craft one Crystal Block. These blocks and shards use 16×16 textures: Legacy's crystal tile for solids and hue-shifted vanilla amethyst sprites for buds and clusters. A page-free Age can also randomly select Crystal Formations; an authored page always retains its exact choice in the saved plan.
 
-Star Fissures are a material-free feature on every terrain profile, including Cave and Void. The fissure is generated once beside the first resolved spawn, using Legacy's spawn-chunk offset and 10–17 paired, irregular X-span rows running along +Z. Each portal tile is placed at y=0 and its column is opened to the sky, as in Legacy. For modern terrain with a surface below y=0, the portal uses the minimum build height plus one instead; empty Void columns keep y=0. Its non-solid portal links to the Overworld spawn with the Legacy fissure sound; the animated starfield is drawn with Minecraft's current End Portal renderer, which uses the same end-sky/end-portal art as Legacy's custom renderer. Random Ages sample Legacy's default small-feature grammar for fissure selection: the stop/one/repeat branches have rank-derived weights 1:1:3, and the fissure has weight 1 of 9 among its small-feature rules. The remainder of random feature selection still follows Rivencraft's current pipeline, rather than running Legacy's entire Age grammar.
+Star Fissures are a material-free feature on every terrain profile, including Cave and Void. The fissure is generated once beside the first resolved spawn, using Legacy's spawn-chunk offset and 10–17 paired, irregular X-span rows running along +Z. Legacy's y=0 portal floor maps to the modern dimension's minimum build height, replacing lower bedrock if present. The rift opens to the sky on ordinary terrain; in Cave terrain it opens into the cavern but stops below the upper bedrock roof. Water in the carved columns is cleared before the portal is placed. Its non-solid portal links to the Overworld spawn with the Legacy fissure sound; the animated starfield is drawn with Minecraft's current End Portal renderer, which uses the same end-sky/end-portal art as Legacy's custom renderer. Random Ages sample Legacy's default small-feature grammar for fissure selection: the stop/one/repeat branches have rank-derived weights 1:1:3, and the fissure has weight 1 of 9 among its small-feature rules. The remainder of random feature selection still follows Rivencraft's current pipeline, rather than running Legacy's entire Age grammar.
 
 The Rivencraft symbol-page creative tabs read a generated index of bundled symbol definitions and group Pages by each definition's category, except biome-controller roles, which appear in a separate Biome Generation tab rather than the Biome tab. Adding another valid JSON symbol under `src/main/resources/data/rivencraft/rivencraft/symbols/` includes its page in the matching category tab on the next build; a new bundled category receives its own tab. Registry-derived Block and Fluid Pages have separate tabs and both appear in optional JEI. Link Pages have a separate tab. Blank Pages appear in neither the creative tabs nor JEI's ingredient list. The server catalog still decides whether a page is valid for writing. External server data-pack symbols are not included in this bundled index.

gradle.properties

@@ -36,7 +36,7 @@ mod_name=Rivencraft
 # The license of the mod. Review your options at https://choosealicense.com/. All Rights Reserved is the default.
 mod_license=LGPL-3.0-or-later
 # The mod version. Rivencraft uses the x.y.z.b policy documented in README.md.
-mod_version=0.4.19.1
+mod_version=0.4.19.2
 immersive_portals_version=6.0.7
 terrablender_version=4.1.0.8
 serene_seasons_version_id=B6nTjh4b

src/main/java/net/dnorberg/rivencraft/book/AgeDimensionService.java

@@ -103,7 +103,8 @@ public final class AgeDimensionService {
                     .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES))
                     || definition.randomFeatures().stream()
                     .anyMatch(choice -> choice.id().equals(AgeFeatureSelection.STAR_FISSURES))) {
-                StarFissureFeature.generate(level, definition.seed(), spawn);
+                StarFissureFeature.generate(level, definition.seed(), spawn,
+                        AgeBiomeSelection.isCave(runtimeProfile(definition)));
             }
             definition = AgeRegistrySavedData.get(level).setSpawn(definition.id(), spawn);
         }

src/main/java/net/dnorberg/rivencraft/world/AgeFlatChunkGenerator.java

@@ -155,6 +155,8 @@ public final class AgeFlatChunkGenerator extends ChunkGenerator {
     @Override public void applyCarvers(WorldGenRegion level, long seed, RandomState random, BiomeManager biomes,
                                        StructureManager structures, ChunkAccess chunk, GenerationStep.Carving step) { }
     @Override public void spawnOriginalMobs(WorldGenRegion level) { }
+    // Keep vanilla FlatLevelSource's generator API values. Actual layer
+    // placement uses chunk.getMinBuildHeight() above, not this metadata value.
     @Override public int getMinY() { return 0; }
     @Override public int getGenDepth() { return 384; }
     @Override public int getSeaLevel() { return -63; }

src/main/java/net/dnorberg/rivencraft/world/StarFissureFeature.java

@@ -49,29 +49,38 @@ public final class StarFissureFeature {
 
     private static void addRow(List<BlockPos> columns, int originX, int originZ, int row, int left, int right) {
         for (int x = left; x <= right; x++) {
+            // Footprint is a 2D column map; this placeholder Y is never used
+            // for placement. generate() resolves the real floor from the level.
             columns.add(new BlockPos(originX + x, 0, originZ + row * 2));
             columns.add(new BlockPos(originX + x, 0, originZ + row * 2 + 1));
         }
     }
 
-    public static void generate(ServerLevel level, long ageSeed, BlockPos spawn) {
+    public static void generate(ServerLevel level, long ageSeed, BlockPos spawn, boolean caveTerrain) {
         List<BlockPos> columns = footprint(ageSeed, spawn);
-        BlockPos first = columns.getFirst();
-        // 1.12 worlds began at y=0. Modern superflat can sit below it, so use the
-        // modern world floor there. Empty Void columns keep Legacy's y=0 portal.
-        int surface = level.getHeight(Heightmap.Types.WORLD_SURFACE, first.getX(), first.getZ());
-        int minY = level.getMinBuildHeight();
-        int floorY = surface > minY && surface <= 0 ? minY + 1 : Math.max(0, minY + 1);
+        // Legacy's y=0 was its minimum build height. The equivalent in 1.21.1
+        // is the dimension's minimum Y, including the bedrock layer itself.
+        int floorY = level.getMinBuildHeight();
         BlockPos.MutableBlockPos mutable = new BlockPos.MutableBlockPos();
         for (BlockPos column : columns) {
             int top = level.getHeight(Heightmap.Types.WORLD_SURFACE, column.getX(), column.getZ());
-            level.setBlock(mutable.set(column.getX(), floorY, column.getZ()),
-                    ModBlocks.STAR_FISSURE.get().defaultBlockState(), 2);
-            // Legacy clears all blocks above each portal tile to the sky. Heightmap
-            // bounds the same work without iterating already-empty world height.
+            if (caveTerrain) {
+                // Cave terrain has a bedrock roof. Open the fissure into the
+                // cavern, but never punch through its upper boundary.
+                for (int y = Math.max(spawn.getY(), floorY + 1); y < top; y++) {
+                    if (level.getBlockState(mutable.set(column.getX(), y, column.getZ())).is(Blocks.BEDROCK)) {
+                        top = y;
+                        break;
+                    }
+                }
+            }
+            // Clear the full column first, including water. Place the portal
+            // last so an existing fluid cannot occupy its block during carving.
             for (int y = floorY + 1; y < top; y++) {
                 level.setBlock(mutable.set(column.getX(), y, column.getZ()), Blocks.AIR.defaultBlockState(), 2);
             }
+            level.setBlock(mutable.set(column.getX(), floorY, column.getZ()),
+                    ModBlocks.STAR_FISSURE.get().defaultBlockState(), 2);
         }
     }
 }