Matched regions by biome category

- For land biomes with known categories, the region climate tie-breaker averages only the region's templates that share a category with the mod biome, so a mixed region no longer looks temperate on average
- A small region affinity term favors regions whose templates share the mod biome's categories

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

@@ -27,6 +27,7 @@ import com.google.gson.JsonObject;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -42,6 +43,7 @@ final class ModBiomeAdopter {
     private static final int VEGETAL_STEP = IrisDecorationStep.VEGETAL_DECORATION.ordinal();
     private static final double CATEGORY_WEIGHT = 1D;
     private static final double REGION_CLIMATE_WEIGHT = 0.25D;
+    private static final double REGION_CATEGORY_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;
@@ -107,8 +109,10 @@ final class ModBiomeAdopter {
             if (excludedRegions.contains(region.key())) {
                 continue;
             }
+            IngestClimate regionClimate = regionClimate(region, role, categories);
             double regionPenalty = (themedRegions.contains(region.key()) ? THEMED_REGION_PENALTY : 0D)
-                    + (region.climate() == null ? 0D : REGION_CLIMATE_WEIGHT * climate.distance(region.climate()));
+                    + (regionClimate == null ? 0D : REGION_CLIMATE_WEIGHT * climate.distance(regionClimate))
+                    + REGION_CATEGORY_WEIGHT * (1D - regionAffinity(region, role, categories));
             for (String template : region.pool(role)) {
                 IngestClimate templateClimate = model.biomeClimate(template);
                 double score = climate.distance(templateClimate == null ? region.climate() : templateClimate)
@@ -125,6 +129,34 @@ final class ModBiomeAdopter {
         return best;
     }
 
+    private IngestClimate regionClimate(IngestPackModel.RegionProfile region, BiomeRole role, Set<String> categories) {
+        if (role != BiomeRole.LAND || categories.isEmpty()) {
+            return region.climate();
+        }
+        List<IngestClimate> shared = new ArrayList<>();
+        for (String template : region.pool(BiomeRole.LAND)) {
+            IngestClimate templateClimate = model.biomeClimate(template);
+            if (templateClimate != null && !Collections.disjoint(model.biomeCategories(template), categories)) {
+                shared.add(templateClimate);
+            }
+        }
+        return shared.isEmpty() ? region.climate() : IngestClimate.average(shared);
+    }
+
+    private double regionAffinity(IngestPackModel.RegionProfile region, BiomeRole role, Set<String> categories) {
+        List<String> pool = region.pool(role);
+        if (categories.isEmpty() || pool.isEmpty()) {
+            return 1D;
+        }
+        int shared = 0;
+        for (String template : pool) {
+            if (!Collections.disjoint(model.biomeCategories(template), categories)) {
+                shared++;
+            }
+        }
+        return shared / (double) pool.size();
+    }
+
     private static Set<String> themedRegions(List<IngestPackModel.RegionProfile> regions) {
         if (regions.isEmpty()) {
             return Set.of();

core/src/test/java/art/arcane/iris/pack/ingest/IngestRegionAffinityTest.java

@@ -0,0 +1,112 @@
+/*
+ * Iris is a World Generator for Minecraft Bukkit Servers
+ * Copyright (c) 2022 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.pack.ingest;
+
+import art.arcane.iris.pack.ingest.catalog.CatalogBiome;
+import art.arcane.iris.pack.ingest.catalog.CatalogDimensionType;
+import art.arcane.iris.pack.ingest.catalog.CatalogNamespace;
+import art.arcane.iris.pack.ingest.catalog.WorldgenCatalog;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.Assert.assertTrue;
+
+public class IngestRegionAffinityTest {
+    private static final String MOD = "modisles";
+
+    @Rule
+    public TemporaryFolder folder = new TemporaryFolder();
+
+    @Test
+    public void modBiomeJoinsTheRegionWhoseTemplatesShareItsCategory() throws Exception {
+        Path root = folder.getRoot().toPath();
+        Path source = root.resolve("source");
+        ModIngestFixture.write(source, "dimensions/overworld.json", """
+                {"name": "Overworld", "environment": "NORMAL", "regions": ["temperate", "hot", "cold", "wet", "magnetic", "mushroom"],
+                 "dimensionHeight": {"min": -64, "max": 320}}
+                """);
+        region(source, "temperate", 1, List.of("temperate/plains"));
+        region(source, "hot", 1, List.of("hot/desert"));
+        region(source, "cold", 1, List.of("cold/snow"));
+        region(source, "wet", 1, List.of("wet/swamp"));
+        region(source, "magnetic", 15, List.of("magnetic/mycelium", "magnetic/plains", "magnetic/frozen", "magnetic/marsh"));
+        region(source, "mushroom", 15, List.of("mushroom/fields", "mushroom/forest", "mushroom/crimson", "mushroom/warped"));
+        biome(source, "temperate/plains", "minecraft:plains");
+        biome(source, "hot/desert", "minecraft:desert");
+        biome(source, "cold/snow", "minecraft:snowy_plains");
+        biome(source, "wet/swamp", "minecraft:swamp");
+        biome(source, "magnetic/mycelium", "minecraft:mushroom_fields");
+        biome(source, "magnetic/plains", "minecraft:plains");
+        biome(source, "magnetic/frozen", "minecraft:snowy_plains");
+        biome(source, "magnetic/marsh", "minecraft:swamp");
+        biome(source, "mushroom/fields", "minecraft:mushroom_fields");
+        biome(source, "mushroom/forest", "minecraft:mushroom_fields");
+        biome(source, "mushroom/crimson", "minecraft:crimson_forest");
+        biome(source, "mushroom/warped", "minecraft:warped_forest");
+        Path target = root.resolve("packs").resolve("isles");
+
+        ModIngestReport report = ModIngester.ingest(new ModIngestRequest(source, target, "overworld", catalog(), Set.of(MOD), Set.of(), false));
+
+        String reason = ModIngestFixture.item(report, MOD + ":mirage_isles").reason();
+        assertTrue(reason, reason.contains("in region mushroom "));
+    }
+
+    private static void region(Path pack, String key, int rarity, List<String> land) throws IOException {
+        StringBuilder pool = new StringBuilder();
+        for (String biome : land) {
+            pool.append(pool.isEmpty() ? "" : ", ").append('"').append(biome).append('"');
+        }
+        ModIngestFixture.write(pack, "regions/" + key + ".json", "{\"name\": \"" + key + "\", \"rarity\": " + rarity + ", \"landBiomes\": [" + pool + "]}");
+    }
+
+    private static void biome(Path pack, String key, String derivative) throws IOException {
+        ModIngestFixture.write(pack, "biomes/" + key + ".json", "{\"name\": \"" + key + "\", \"derivative\": \"" + derivative + "\"}");
+    }
+
+    private static WorldgenCatalog catalog() {
+        List<CatalogBiome> biomes = new ArrayList<>();
+        biomes.add(biome("minecraft:plains", 0.8F, 0.4F, "c:is_plains"));
+        biomes.add(biome("minecraft:desert", 2.0F, 0.0F, "c:is_desert"));
+        biomes.add(biome("minecraft:snowy_plains", 0.0F, 0.5F, "c:is_snowy"));
+        biomes.add(biome("minecraft:swamp", 0.8F, 0.9F, "c:is_swamp"));
+        biomes.add(biome("minecraft:mushroom_fields", 0.9F, 1.0F, "c:is_mushroom"));
+        biomes.add(biome("minecraft:crimson_forest", 2.0F, 0.0F, "c:is_nether"));
+        biomes.add(biome("minecraft:warped_forest", 2.0F, 0.0F, "c:is_nether"));
+        biomes.add(biome(MOD + ":mirage_isles", 0.7F, 0.8F, "c:is_mushroom"));
+        return new WorldgenCatalog(WorldgenCatalog.FORMAT, "26.3", "fabric", 1L, "affinity",
+                List.of(new CatalogNamespace(MOD, "Mod Isles", "1")), biomes, List.of(), List.of(),
+                List.of(new CatalogDimensionType("minecraft:overworld", -64, 384, 384, null)), List.of(), Map.of());
+    }
+
+    private static CatalogBiome biome(String key, float temperature, float downfall, String categoryTag) {
+        List<List<String>> steps = new ArrayList<>(11);
+        for (int index = 0; index < 11; index++) {
+            steps.add(List.of());
+        }
+        return new CatalogBiome(key, temperature, downfall, true, List.of("minecraft:is_overworld", categoryTag), steps, List.of(), null);
+    }
+}