Kept mod trees on plantable ground

- A mod biome that brings its own vegetation pays a template penalty scaled by the share of the template's top surface layer that cannot hold plants, so snow, ice, sand, and stone templates no longer swallow its trees
- The top layer palette is resolved through biome-palette snippets and weighted by palette entry weight
- Mod biomes without their own vegetation keep the closest climate template

core/src/main/java/art/arcane/iris/pack/ingest/IngestPackModel.java

@@ -29,6 +29,7 @@ import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumMap;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
@@ -40,6 +41,9 @@ final class IngestPackModel {
     private static final int DEFAULT_MIN_Y = -64;
     private static final int DEFAULT_MAX_Y = 320;
     private static final String DEFAULT_DERIVATIVE = "minecraft:the_void";
+    private static final Set<String> PLANTABLE_BLOCKS = Set.of("minecraft:grass_block", "minecraft:dirt", "minecraft:coarse_dirt",
+            "minecraft:podzol", "minecraft:rooted_dirt", "minecraft:mycelium", "minecraft:moss_block", "minecraft:pale_moss_block",
+            "minecraft:mud", "minecraft:muddy_mangrove_roots", "minecraft:farmland");
 
     private final IngestPack pack;
     private final WorldgenCatalogIndex index;
@@ -50,6 +54,7 @@ final class IngestPackModel {
     private final int packMaxY;
     private final List<RegionProfile> regions;
     private final Map<String, String> reachableBiomes;
+    private final Map<String, Double> plantableShares = new HashMap<>();
 
     private IngestPackModel(IngestPack pack, WorldgenCatalogIndex index, String dimensionPath, JsonObject dimension,
                             int[] heightRange, List<RegionProfile> regions, Map<String, String> reachableBiomes) {
@@ -115,6 +120,42 @@ final class IngestPackModel {
         return climateReference(index, reachableBiomes.get(biomeKey)).map(IngestClimate::of).orElse(null);
     }
 
+    double plantableShare(String biomeKey) throws IOException {
+        Double cached = plantableShares.get(biomeKey);
+        if (cached != null) {
+            return cached;
+        }
+        double share = topLayerPlantableShare(biomeKey);
+        plantableShares.put(biomeKey, share);
+        return share;
+    }
+
+    private double topLayerPlantableShare(String biomeKey) throws IOException {
+        Optional<JsonObject> biome = pack.find(IngestPack.biomePath(biomeKey));
+        JsonElement layers = biome.map((JsonObject value) -> value.get("layers")).orElse(null);
+        if (layers == null || !layers.isJsonArray() || layers.getAsJsonArray().isEmpty()) {
+            return 1D;
+        }
+        JsonObject top = pack.snippet(layers.getAsJsonArray().get(0), "biome-palette");
+        JsonElement palette = top == null ? null : top.get("palette");
+        if (palette == null || !palette.isJsonArray() || palette.getAsJsonArray().isEmpty()) {
+            return 1D;
+        }
+        double total = 0D;
+        double plantable = 0D;
+        for (JsonElement entry : palette.getAsJsonArray()) {
+            if (!entry.isJsonObject() || !entry.getAsJsonObject().has("block")) {
+                continue;
+            }
+            double weight = Math.max(0D, number(entry.getAsJsonObject().get("weight"), 1D));
+            total += weight;
+            if (PLANTABLE_BLOCKS.contains(VanillaJson.namespaced(entry.getAsJsonObject().get("block").getAsString()))) {
+                plantable += weight;
+            }
+        }
+        return total <= 0D ? 1D : plantable / total;
+    }
+
     Set<String> biomeCategories(String biomeKey) {
         return climateReference(index, reachableBiomes.get(biomeKey)).map((CatalogBiome biome) -> BiomeCategories.of(biome.tags())).orElse(Set.of());
     }

core/src/main/java/art/arcane/iris/pack/ingest/ModBiomeAdopter.java

@@ -44,6 +44,7 @@ final class ModBiomeAdopter {
     private static final double REGION_CLIMATE_WEIGHT = 0.25D;
     private static final double REUSE_WEIGHT = 0.05D;
     private static final double THEMED_REGION_PENALTY = 0.6D;
+    private static final double BARE_SURFACE_PENALTY = 3D;
     private static final int THEMED_RARITY_FACTOR = 5;
 
     private final IngestPackModel model;
@@ -71,7 +72,8 @@ final class ModBiomeAdopter {
                 continue;
             }
             BiomeRole role = classification.role();
-            Placement placement = place(role, IngestClimate.of(biome), BiomeCategories.of(biome.tags()));
+            boolean ownsVegetation = ownsVegetation(biome, namespace);
+            Placement placement = place(role, IngestClimate.of(biome), BiomeCategories.of(biome.tags()), ownsVegetation);
             if (placement == null) {
                 items.add(new ModIngestItem(namespace, biome.key(), "biome", ModIngestTier.SKIPPED, "",
                         "no region in this dimension accepts a " + role.label() + " biome"));
@@ -82,7 +84,7 @@ final class ModBiomeAdopter {
             templateUses.merge(template, 1, Integer::sum);
             String irisKey = irisKey(biome.key());
             JsonObject json = model.pack().require(IngestPack.biomePath(template)).deepCopy();
-            transform(json, biome, ownsVegetation(biome, namespace));
+            transform(json, biome, ownsVegetation);
             model.pack().create(IngestPack.biomePath(irisKey), json);
             appendToPool(region.key(), role, irisKey);
             adopted.put(biome.key(), new AdoptedBiome(biome.key(), irisKey, role, region.key()));
@@ -98,7 +100,7 @@ final class ModBiomeAdopter {
         return INGEST_BIOME_FOLDER + namespace + "/" + modBiomeKey.substring(colon + 1);
     }
 
-    private Placement place(BiomeRole role, IngestClimate climate, Set<String> categories) {
+    private Placement place(BiomeRole role, IngestClimate climate, Set<String> categories, boolean ownsVegetation) throws IOException {
         Placement best = null;
         double bestScore = Double.POSITIVE_INFINITY;
         for (IngestPackModel.RegionProfile region : model.regions()) {
@@ -112,6 +114,7 @@ final class ModBiomeAdopter {
                 double score = climate.distance(templateClimate == null ? region.climate() : templateClimate)
                         + CATEGORY_WEIGHT * BiomeCategories.distance(categories, model.biomeCategories(template))
                         + REUSE_WEIGHT * templateUses.getOrDefault(template, 0)
+                        + (ownsVegetation ? BARE_SURFACE_PENALTY * (1D - model.plantableShare(template)) : 0D)
                         + regionPenalty;
                 if (best == null || score < bestScore) {
                     best = new Placement(region, template);