Adjust structure placement in GoG skyblock

Fixes #4712 using code snippets from Carpet Skyblock Additions that use the original noise generator to emulate the non-skyblock heightmap for placing height-sensitive structures.

Xplat/src/main/java/vazkii/botania/common/world/SkyblockChunkGenerator.java

@@ -12,16 +12,18 @@
 import com.mojang.serialization.codecs.RecordCodecBuilder;
 
 import net.minecraft.core.*;
+import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.server.level.ServerChunkCache;
 import net.minecraft.server.level.WorldGenRegion;
 import net.minecraft.world.level.*;
 import net.minecraft.world.level.biome.*;
-import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.chunk.*;
 import net.minecraft.world.level.levelgen.*;
 import net.minecraft.world.level.levelgen.blending.Blender;
 
+import org.jetbrains.annotations.NotNull;
+
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
 import java.util.function.BiConsumer;
@@ -48,39 +50,44 @@ private SkyblockChunkGenerator(BiomeSource biomeSource, Holder<NoiseGeneratorSet
 		super(biomeSource, settings);
 	}
 
+	@NotNull
 	@Override
 	protected Codec<? extends ChunkGenerator> codec() {
 		return CODEC;
 	}
 
 	@Override
-	public int getBaseHeight(int x, int z, Heightmap.Types heightmapTypes, LevelHeightAccessor levelHeightAccessor, RandomState randomState) {
-		return levelHeightAccessor.getMinBuildHeight();
-	}
-
-	@Override
-	public NoiseColumn getBaseColumn(int x, int z, LevelHeightAccessor levelHeightAccessor, RandomState randomState) {
-		return new NoiseColumn(levelHeightAccessor.getMinBuildHeight(), new BlockState[0]);
-	}
-
-	@Override
-	public void buildSurface(ChunkAccess chunkAccess, WorldGenerationContext context,
-			RandomState randomState, StructureManager structureManager, BiomeManager biomeManager,
-			Registry<Biome> biomes, Blender blender) {}
+	public void buildSurface(@NotNull ChunkAccess chunkAccess, @NotNull WorldGenerationContext context,
+			@NotNull RandomState randomState, @NotNull StructureManager structureManager,
+			@NotNull BiomeManager biomeManager, @NotNull Registry<Biome> biomes, @NotNull Blender blender) {}
 
 	@Override
-	public void applyCarvers(WorldGenRegion worldGenRegion, long seed, RandomState randomState, BiomeManager biomeManager, StructureManager structureManager, ChunkAccess chunkAccess, GenerationStep.Carving carving) {
-
-	}
+	public void applyCarvers(@NotNull WorldGenRegion worldGenRegion, long seed, @NotNull RandomState randomState,
+			@NotNull BiomeManager biomeManager, @NotNull StructureManager structureManager,
+			@NotNull ChunkAccess chunkAccess, GenerationStep.@NotNull Carving carving) {}
 
 	@Override
-	public CompletableFuture<ChunkAccess> fillFromNoise(Executor executor, Blender blender, RandomState randomState, StructureManager structureManager, ChunkAccess chunk) {
+	public @NotNull CompletableFuture<ChunkAccess> fillFromNoise(@NotNull Executor executor, @NotNull Blender blender,
+			@NotNull RandomState randomState, @NotNull StructureManager structureManager, @NotNull ChunkAccess chunk) {
 		return CompletableFuture.completedFuture(chunk);
 	}
 
 	@Override
-	public void spawnOriginalMobs(WorldGenRegion region) {}
+	public void spawnOriginalMobs(@NotNull WorldGenRegion region) {}
 
 	@Override
-	public void applyBiomeDecoration(WorldGenLevel level, ChunkAccess chunkAccess, StructureManager structureManager) {}
+	public void applyBiomeDecoration(@NotNull WorldGenLevel level, @NotNull ChunkAccess chunkAccess,
+			@NotNull StructureManager structureManager) {}
+
+	/**
+	 * Calculates the height at a particular location as it would be in a world with the same seed that isn't empty.
+	 * (Based on code from CarpetSkyAdditions.)
+	 */
+	public int getBaseHeightInEquivalentNoiseWorld(int x, int z, Heightmap.Types heightmap, WorldGenLevel level) {
+		RandomState randomState = RandomState.create(
+				generatorSettings().value(),
+				level.registryAccess().registryOrThrow(Registries.NOISE).asLookup(),
+				level.getSeed());
+		return super.getBaseHeight(x, z, heightmap, level, randomState);
+	}
 }

Xplat/src/main/java/vazkii/botania/mixin/PlacementContextMixin.java

@@ -0,0 +1,45 @@
+package vazkii.botania.mixin;
+
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.levelgen.Heightmap;
+import net.minecraft.world.level.levelgen.WorldGenerationContext;
+import net.minecraft.world.level.levelgen.placement.PlacementContext;
+
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import vazkii.botania.common.world.SkyblockChunkGenerator;
+
+/**
+ * Based on code from CarpetSkyAdditions. Ensures terrain-sensitive structures generate where they should.
+ */
+@Mixin(PlacementContext.class)
+public class PlacementContextMixin extends WorldGenerationContext {
+	@Shadow
+	@Final
+	private ChunkGenerator generator;
+
+	@Shadow
+	@Final
+	private WorldGenLevel level;
+
+	public PlacementContextMixin(ChunkGenerator generator, LevelHeightAccessor levelHeightAccessor) {
+		super(generator, levelHeightAccessor);
+	}
+
+	/**
+	 * For Garden of Glass, use generation heightmap instead of empty actual heightmap to place features/structures.
+	 */
+	@Inject(method = "getHeight", cancellable = true, at = @At("HEAD"))
+	private void useGenerationHeightmap(Heightmap.Types heightmap, int x, int z, CallbackInfoReturnable<Integer> cir) {
+		if (generator instanceof SkyblockChunkGenerator skyblockChunkGenerator) {
+			cir.setReturnValue(skyblockChunkGenerator.getBaseHeightInEquivalentNoiseWorld(x, z, heightmap, level));
+		}
+	}
+}

Xplat/src/main/resources/botania_xplat.mixins.json

@@ -43,6 +43,7 @@
     "PistonBaseBlockAccessor",
     "PistonBaseBlockMixin",
     "PistonStructureResolverMixin",
+    "PlacementContextMixin",
     "PlayerMixin",
     "PollinateGoalMixin",
     "ProtectionEnchantmentMixin",