# Minecraft Fabric Modding - 世界生成

## 礦物生成

在模組路徑下的 `world/feature/ore` 建立檔案 `ModOreFeature.java`：

public class ModOreFeatures {
    public static List<PlacementModifier> modifiers(PlacementModifier countModifier, PlacementModifier heightModifier) {
        return List.of(countModifier, SquarePlacementModifier.of(), heightModifier, BiomePlacementModifier.of());
    }

    public static List<PlacementModifier> modifiersWithCount(int count, PlacementModifier heightModifier) {
        return modifiers(CountPlacementModifier.of(count), heightModifier);
    }

    public static List<PlacementModifier> modifiersWithRarity(int chance, PlacementModifier heightModifier) {
        return modifiers(RarityFilterPlacementModifier.of(chance), heightModifier);
    }
}

再來，於 `world/feature` 下建立檔案 `ModOreGeneration.java`：

public class ModOreGeneration {

    public static void generateOres() {
        generator("lead_ore", new OreGenerationReference(
                List.of(new Pair<>(ModBlocks.LEAD_ORE, OreConfiguredFeatures.STONE_ORE_REPLACEABLES),
                        new Pair<>(ModBlocks.LEAD_ORE, OreConfiguredFeatures.DEEPSLATE_ORE_REPLACEABLES)),
                BiomeSelectors.foundInOverworld(), GenerationStep.Feature.UNDERGROUND_ORES,
                8, // Vein Size
                7, // Veins Per Chunk
                HeightRangePlacementModifier.trapezoid(YOffset.aboveBottom(-80), YOffset.aboveBottom(80))
                // HeightRangePlacementModifier 有很多不同種的生成分布方式。像 trapezoid 就是梯形分布，上下最少，中間最多
        ));
    }

    public record OreGenerationReference(List<Pair<Block, RuleTest>> BRP_list, Predicate<BiomeSelectionContext> biomeSelection,
                                          GenerationStep.Feature step, int veinSize, int veinsPerChunk,
                                         HeightRangePlacementModifier modifier) {}

    public static void generator(String name, OreGenerationReference ref) {
        List<OreFeatureConfig.Target> list = new ArrayList<>();
        for (Pair<Block, RuleTest> p : ref.BRP_list)
            list.add(OreFeatureConfig.createTarget(p.getRight(), p.getLeft().getDefaultState()));

        RegistryEntry<ConfiguredFeature<OreFeatureConfig, ?>> ORE =
                ConfiguredFeatures.register(name, Feature.ORE, new OreFeatureConfig(list, ref.veinSize));

        RegistryEntry<PlacedFeature> ORE_PLACED = PlacedFeatures.register(name + "_placed", ORE,
                ModOreFeatures.modifiersWithCount(ref.veinsPerChunk, ref.modifier));

        BiomeModifications.addFeature(ref.biomeSelection, ref.step, ORE_PLACED.getKey().get());
    }

    // utilities
    private static List<Pair<Block, RuleTest>> getOverworldList(Block block) {
        return List.of(new Pair<>(block, OreConfiguredFeatures.STONE_ORE_REPLACEABLES),
                new Pair<>(block, OreConfiguredFeatures.DEEPSLATE_ORE_REPLACEABLES));
    }
    private static final HeightRangePlacementModifier huAll = HeightRangePlacementModifier.uniform(YOffset.BOTTOM, YOffset.TOP);
}

## 結構生成

### .nbt 檔
在 Minecraft 中，我們常用 nbt 檔來存儲結構資料。nbt 檔是一種二進位檔，可用 [NBTExplorer](https://github.com/jaquadro/NBTExplorer/releases) 瀏覽其中資料。

### 結構方塊與拼圖方塊
[Talon - How to Use Jigsaw Blocks](https://www.youtube.com/watch?v=5a4DAkWW3JQ&ab_channel=Talon)

:::warning
以下皆以單結構方塊為主，也就是未使用拼圖方塊
:::

### code
在模組 java 路徑下，新增 `world/structures`，並新增兩個檔案 `AltarStructure`、`ModStructures`

public class AltarStructure extends StructureFeature<StructurePoolFeatureConfig> {

    public AltarStructure() {
        super(StructurePoolFeatureConfig.CODEC, AltarStructure::createPiecesGenerator, PostPlacementProcessor.EMPTY);
    }

    private static boolean isFeatureChunk(StructureGeneratorFactory.Context<StructurePoolFeatureConfig> context) {
        // Grabs the chunk position we are at
        ChunkPos chunkpos = context.chunkPos();

        // Checks to make sure our structure does not spawn within 10 chunks of an Ocean Monument
        // to demonstrate how this method is good for checking extra conditions for spawning
        return !context.chunkGenerator().method_41053(StructureSetKeys.VILLAGES, context.seed(), chunkpos.x, chunkpos.z, 10);
    }

    public static Optional<StructurePiecesGenerator<StructurePoolFeatureConfig>> createPiecesGenerator(StructureGeneratorFactory.Context<StructurePoolFeatureConfig> context) {
        
        // Check if the spot is valid for our structure. This is just as another method for cleanness.
        // Returning an empty optional tells the game to skip this spot as it will not generate the structure.
        if (!AltarStructure.isFeatureChunk(context))
            return Optional.empty();

        // Turns the chunk coordinates into actual coordinates we can use. (Gets center of that chunk)
        BlockPos blockpos = context.chunkPos().getCenterAtY(0);
        
        // Find the top Y value of the land and then offset our structure to 60 blocks above that.
        int topLandY = context.chunkGenerator().getHeightOnGround(blockpos.getX(), blockpos.getZ(), Heightmap.Type.WORLD_SURFACE_WG, context.world());

        Optional<StructurePiecesGenerator<StructurePoolFeatureConfig>> structurePiecesGenerator = StructurePoolBasedGenerator.generate(
                context, // Used for JigsawPlacement to get all the proper behaviors done.
                PoolStructurePiece::new, // Needed in order to create a list of jigsaw pieces when making the structure's layout.
                blockpos, // Position of the structure. Y value is ignored if last parameter is set to true.
                false,  // Special boundary adjustments for villages. It's... hard to explain. Keep this false and make your pieces not be partially intersecting.
                        // Either not intersecting or fully contained will make children pieces spawn just fine. It's easier that way.
                true // Place at heightmap (top land). Set this to false for structure to be place at the passed in blockpos's Y value instead.
                     // Definitely keep this false when placing structures in the nether as otherwise, heightmap placing will put the structure on the Bedrock roof.
        );

        /*
         * Note, you are always free to make your own JigsawPlacement class and implementation of how the structure
         * should generate. It is tricky but extremely powerful if you are doing something that vanilla's jigsaw system cannot do.
         * Such as for example, forcing 3 pieces to always spawn every time, limiting how often a piece spawns, or remove the intersection limitation of pieces.
         *
         * An example of a custom JigsawPlacement.addPieces in action can be found here (warning, it is using Mojmap mappings):
         * https://github.com/TelepathicGrunt/RepurposedStructures/blob/1.18.2/src/main/java/com/telepathicgrunt/repurposedstructures/world/structures/pieces/PieceLimitedJigsawManager.java
         */
        if (structurePiecesGenerator.isPresent()) {
            System.out.println("Mod Structure");
        }
        
        // Return the pieces generator that is now set up so that the game runs it when it needs to create the layout of structure pieces.
        return structurePiecesGenerator;
    }
}

public class ModStructures {

    public static StructureFeature<?> ALTAR_STRUCTURE = new AltarStructure();

    public static void registerStructureFeatures() {
        StructureFeatureAccessor.callRegister(More_Ores.MOD_ID + ":altar_structure", ALTAR_STRUCTURE, GenerationStep.Feature.SURFACE_STRUCTURES);
    }
}

最後再將 `registerStructureFeatures()` 加入主程式中即可

### Mixin

以 `interface` 的形式加入檔案 `StructureFeatureAccessor.java`

@Mixin(StructureFeature.class)
public interface StructureFeatureAccessor {
    @Invoker
    static <F extends StructureFeature<?>> F callRegister(String name, F structureFeature, GenerationStep.Feature step) {
        throw new UnsupportedOperationException();
    }
}

記得在 `<ModId>.mixin.json` 的 `mixins` 內加入 `"StructureFeatureAccessor"`

{
  ...
  "mixins": [
    ...
    "StructureFeatureAccessor"
  ],
  ...
}

### json

檔案位置：

resource
└─ data
   └─ <ModId>
      ├─ structures
      │  └─ altar.nbt
      │
      ├─ tags/worldgen/biome/has_structure
      │  └─ altar_biomes.json
      │
      └─ worldgen
         ├─ configured_structure_feature
         │  └─ altar.json
         │
         ├─ structure_set
         │  └─ altar.json
         │
         └─ template_pool
            └─ altar_start_pool.json

#### `configured_structure_feature/altar.json`：

{
  "type": "more_ores:altar_structure",

  "config": {
    "start_pool": "more_ores:altar_start_pool",
    "size": 1
  },

  "biomes": "#more_ores:has_structure/altar_biomes",

  "adapt_noise": true,

  "spawn_overrides": {
  }
}

`type` 是根據你在 `ModStructures` 註冊之結構類型之名稱
`start_pool` 為 `start_pool` 的路徑
`size` 是在有拼圖方塊時之生成大小
`biomes` 是指定結構生成的生態域，自訂檔案位置如上
`adapt_noise` 若為真，會生成於地表附近
`spawn_overrides` 可指定甚麼生物可生成於此結構

:::danger
***spawn_overrides 為必要元素，請務必記得加入！！***
:::

#### `tags/worldgen/biome/has_structure/altar_biomes.json`：

{
  "replace": false,

  "values": [
    "#minecraft:desert",
    "#minecraft:forest",
    "#minecraft:taiga",
    "#minecraft:savanna",
    "#minecraft:jungle"
  ]
}

#### `structure_set/altar.json`：

{
  "structures": [
    {
      "structure": "more_ores:altar",
      "weight": 1
    }
  ],
  "placement": {
    "salt": 601684253,

    "spacing": 50,

    "separation": 20,

    "type": "minecraft:random_spread"
  }
}

`structures` 中可放入數個結構，通常用於生成拼圖方塊結構
`salt` 修改結構種子，使兩結構不重疊。使其大而獨特! [質數產生器](https://bigprimes.org/)
`spacing` 代表生成的平均距離(chunk)
`seperation` 代表生成結構的最小間隔(chunk)，**必須小於 spacing**
`type` 為生成形式

#### `template_pool/altar_start_pool.json`：

{
  "name": "more_ores:altar_start_pool",
  "fallback": "minecraft:empty",

  "elements": [
    {
      "weight": 1,
      "element": {
        "location": "more_ores:altar",
        "processors": "minecraft:empty",
        "projection": "rigid",
        "element_type": "minecraft:single_pool_element"
      }
    }
  ]
}

`location` 為結構 nbt 檔位置
`processors` 可隨機生成一些方塊於結構中，使結構更加自然，詳見[參考檔案](https://github.com/TelepathicGrunt/StructureTutorialMod/blob/1.18.2-Fabric-Jigsaw/src/main/resources/data/structure_tutorial/worldgen/processor_list/randomize_stonebrick.json)

## Feature

##

## 參考資料
[TelepathicGrunt - StructureTutorialMod](https://github.com/TelepathicGrunt/StructureTutorialMod/tree/1.18.0-Fabric-Jigsaw)

---
###### tags: `Minecraft Fabric Modding`