AlterGroundEvent for modifying block placement performed by AlterGroundDecorator (#9637)

patches/minecraft/net/minecraft/world/level/levelgen/feature/treedecorators/AlterGroundDecorator.java.patch

@@ -0,0 +1,11 @@
+--- a/net/minecraft/world/level/levelgen/feature/treedecorators/AlterGroundDecorator.java
++++ b/net/minecraft/world/level/levelgen/feature/treedecorators/AlterGroundDecorator.java
+@@ -72,7 +_,7 @@
+       for(int i = 2; i >= -3; --i) {
+          BlockPos blockpos = p_225975_.m_6630_(i);
+          if (Feature.m_65788_(p_225974_.m_226058_(), blockpos)) {
+-            p_225974_.m_226061_(blockpos, this.f_69303_.m_213972_(p_225974_.m_226067_(), p_225975_));
++            p_225974_.m_226061_(blockpos, net.minecraftforge.event.ForgeEventFactory.alterGround(p_225974_.m_226058_(), p_225974_.m_226067_(), blockpos, this.f_69303_.m_213972_(p_225974_.m_226067_(), p_225975_)));
+             break;
+          }
+ 

src/main/java/net/minecraftforge/event/ForgeEventFactory.java

@@ -30,6 +30,7 @@ import net.minecraft.world.DifficultyInstance;
 import net.minecraft.world.entity.MobCategory;
 import net.minecraft.world.entity.projectile.Projectile;
 import net.minecraft.world.entity.projectile.ThrownEnderpearl;
+import net.minecraft.world.level.LevelSimulatedReader;
 import net.minecraft.world.level.biome.MobSpawnSettings;
 import net.minecraft.world.level.chunk.LevelChunk;
 import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
@@ -128,6 +129,7 @@ import net.minecraftforge.event.entity.player.PlayerWakeUpEvent;
 import net.minecraftforge.event.entity.player.SleepingLocationCheckEvent;
 import net.minecraftforge.event.entity.player.SleepingTimeCheckEvent;
 import net.minecraftforge.event.furnace.FurnaceFuelBurnTimeEvent;
+import net.minecraftforge.event.level.AlterGroundEvent;
 import net.minecraftforge.event.level.BlockEvent;
 import net.minecraftforge.event.level.BlockEvent.BlockToolModificationEvent;
 import net.minecraftforge.event.level.BlockEvent.CreateFluidSourceEvent;
@@ -737,6 +739,13 @@ public class ForgeEventFactory
         return event;
     }
 
+    public static BlockState alterGround(LevelSimulatedReader level, RandomSource random, BlockPos pos, BlockState altered)
+    {
+        AlterGroundEvent event = new AlterGroundEvent(level, random, pos, altered);
+        MinecraftForge.EVENT_BUS.post(event);
+        return event.getNewAlteredState();
+    }
+
     public static void fireChunkTicketLevelUpdated(ServerLevel level, long chunkPos, int oldTicketLevel, int newTicketLevel, @Nullable ChunkHolder chunkHolder)
     {
         if (oldTicketLevel != newTicketLevel)

src/main/java/net/minecraftforge/event/level/AlterGroundEvent.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.event.level;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.LevelSimulatedReader;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.levelgen.feature.treedecorators.TreeDecorator;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.eventbus.api.Cancelable;
+import net.minecraftforge.eventbus.api.Event;
+import org.jetbrains.annotations.ApiStatus;
+
+/**
+ * This event is fired when {@link net.minecraft.world.level.levelgen.feature.treedecorators.AlterGroundDecorator#placeBlockAt(TreeDecorator.Context, BlockPos)}
+ * attempts to alter a ground block when generating a feature. An example of this would be large spruce trees converting grass blocks into podzol.
+ * <p>
+ * This event is not {@linkplain Cancelable cancellable}.
+ * <p>
+ * This event is fired on the {@linkplain MinecraftForge#EVENT_BUS main Forge event bus}
+ * only on the {@linkplain net.minecraftforge.fml.LogicalSide#SERVER logical server}.
+ */
+public class AlterGroundEvent extends Event {
+    private final LevelSimulatedReader level;
+    private final RandomSource random;
+    private final BlockPos pos;
+    private final BlockState originalAltered;
+    private BlockState newAltered;
+
+    @ApiStatus.Internal
+    public AlterGroundEvent(LevelSimulatedReader level, RandomSource random, BlockPos pos, BlockState altered) {
+        super();
+        this.level = level;
+        this.random = random;
+        this.pos = pos;
+        this.originalAltered = altered;
+        this.newAltered = altered;
+    }
+
+    public LevelSimulatedReader getLevel() {
+        return this.level;
+    }
+
+    public RandomSource getRandom() {
+        return this.random;
+    }
+
+    /**
+     * {@return the position of the block that will be altered}
+     */
+    public BlockPos getPos() {
+        return this.pos;
+    }
+
+    /**
+     * {@return the original block state that would be placed by the ground decorator}
+     */
+    public BlockState getOriginalAlteredState() {
+        return this.originalAltered;
+    }
+
+    /**
+     * {@return the new block state to be placed by the ground decorator}
+     */
+    public BlockState getNewAlteredState() {
+        return this.newAltered;
+    }
+
+    /**
+     * @param newAltered the new block state to be placed by the ground decorator
+     */
+    public void setNewAlteredState(BlockState newAltered) {
+        this.newAltered = newAltered;
+    }
+}

src/test/java/net/minecraftforge/debug/AlterGroundEventTest.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.debug;
+
+import net.minecraft.world.level.block.Blocks;
+import net.minecraftforge.event.level.AlterGroundEvent;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.common.Mod;
+
+@Mod("alter_ground_event_test")
+@Mod.EventBusSubscriber
+public class AlterGroundEventTest {
+    public static final boolean ENABLE = true;
+
+    @SubscribeEvent
+    public static void onAlterGround(AlterGroundEvent event)
+    {
+        if (ENABLE) {
+            if (event.getOriginalAlteredState().is(Blocks.PODZOL)) {
+                event.setNewAlteredState(Blocks.REDSTONE_BLOCK.defaultBlockState());
+            }
+        }
+    }
+}

src/test/resources/META-INF/mods.toml

@@ -295,5 +295,7 @@ modId="trade_with_villager_event_test"
 modId="chunk_event_load_new_chunk_test"
 [[mods]]
 modId="custom_fluid_container_test"
+[[mods]]
+modId="alter_ground_event_test"
 
 # ADD ABOVE THIS LINE