Add ExplosionKnockbackEvent (#1017)

patches/net/minecraft/world/level/Explosion.java.patch

@@ -8,3 +8,11 @@
          Vec3 vec3 = new Vec3(this.x, this.y, this.z);
 
          for (Entity entity : list) {
+@@ -298,6 +_,7 @@
+                         d7 *= d10;
+                         d9 *= d10;
+                         Vec3 vec31 = new Vec3(d5, d7, d9);
++                        vec31 = net.neoforged.neoforge.event.EventHooks.getExplosionKnockback(this.level, this, entity, vec31);
+                         entity.setDeltaMovement(entity.getDeltaMovement().add(vec31));
+                         if (entity instanceof Player) {
+                             Player player = (Player)entity;

src/main/java/net/neoforged/neoforge/event/EventHooks.java

@@ -164,6 +164,7 @@
 import net.neoforged.neoforge.event.level.ChunkTicketLevelUpdatedEvent;
 import net.neoforged.neoforge.event.level.ChunkWatchEvent;
 import net.neoforged.neoforge.event.level.ExplosionEvent;
+import net.neoforged.neoforge.event.level.ExplosionKnockbackEvent;
 import net.neoforged.neoforge.event.level.LevelEvent;
 import net.neoforged.neoforge.event.level.PistonEvent;
 import net.neoforged.neoforge.event.level.SleepFinishedTimeEvent;
@@ -598,6 +599,22 @@ public static void onExplosionDetonate(Level level, Explosion explosion, List<En
         NeoForge.EVENT_BUS.post(new ExplosionEvent.Detonate(level, explosion, list));
     }
 
+    /**
+     * To be called when an explosion has calculated the knockback velocity
+     * but has not yet added the knockback to the entity caught in blast.
+     *
+     * @param level           The level that the explosion is in
+     * @param explosion       Explosion that is happening
+     * @param entity          The entity caught in the explosion's blast
+     * @param initialVelocity The explosion calculated velocity for the entity
+     * @return The new explosion velocity to add to the entity's existing velocity
+     */
+    public static Vec3 getExplosionKnockback(Level level, Explosion explosion, Entity entity, Vec3 initialVelocity) {
+        ExplosionKnockbackEvent event = new ExplosionKnockbackEvent(level, explosion, entity, initialVelocity);
+        NeoForge.EVENT_BUS.post(event);
+        return event.getKnockbackVelocity();
+    }
+
     public static boolean onCreateWorldSpawn(Level level, ServerLevelData settings) {
         return NeoForge.EVENT_BUS.post(new LevelEvent.CreateSpawnPosition(level, settings)).isCanceled();
     }

src/main/java/net/neoforged/neoforge/event/level/ExplosionKnockbackEvent.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.event.level;
+
+import java.util.List;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.level.Explosion;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.phys.Vec3;
+import net.neoforged.bus.api.ICancellableEvent;
+import net.neoforged.neoforge.common.NeoForge;
+
+/**
+ * ExplosionKnockbackEvent is fired once the explosion has calculated the knockback velocity to add to the entity caught in blast.<br>
+ * <br>
+ * This event is not {@link ICancellableEvent}.<br>
+ * This event does not use {@link HasResult}.<br>
+ * This event is fired on the {@link NeoForge#EVENT_BUS}.<br>
+ */
+public class ExplosionKnockbackEvent extends ExplosionEvent {
+    private final Entity entity;
+    private Vec3 knockbackVelocity;
+
+    public ExplosionKnockbackEvent(Level level, Explosion explosion, Entity entity, Vec3 knockbackVelocity) {
+        super(level, explosion);
+        this.entity = entity;
+        this.knockbackVelocity = knockbackVelocity;
+    }
+
+    /** return the list of blocks affected by the explosion. */
+    public List<BlockPos> getAffectedBlocks() {
+        return getExplosion().getToBlow();
+    }
+
+    /** return the entity affected by the explosion knockback. */
+    public Entity getAffectedEntity() {
+        return entity;
+    }
+
+    /** return the explosion knockback velocity to apply to entity. */
+    public Vec3 getKnockbackVelocity() {
+        return knockbackVelocity;
+    }
+
+    /** Sets the explosion knockback velocity to add to the entity's existing velocity. */
+    public void setKnockbackVelocity(Vec3 newKnockbackVelocity) {
+        this.knockbackVelocity = newKnockbackVelocity;
+    }
+}

tests/src/main/java/net/neoforged/neoforge/debug/entity/EntityEventTests.java

@@ -5,6 +5,7 @@
 
 package net.neoforged.neoforge.debug.entity;
 
+import net.minecraft.core.BlockPos;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.gametest.framework.GameTest;
 import net.minecraft.world.entity.EntityType;
@@ -13,8 +14,12 @@
 import net.minecraft.world.entity.animal.Pig;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.phys.Vec3;
 import net.neoforged.neoforge.event.entity.EntityAttributeModificationEvent;
 import net.neoforged.neoforge.event.entity.EntityTeleportEvent;
+import net.neoforged.neoforge.event.level.ExplosionKnockbackEvent;
 import net.neoforged.testframework.DynamicTest;
 import net.neoforged.testframework.annotation.ForEachTest;
 import net.neoforged.testframework.annotation.TestHolder;
@@ -69,4 +74,23 @@ static void entityAttributeModificationEvent(final DynamicTest test, final Regis
                         donkey, d -> d.getAttribute(testAttr).getValue(), "test attribute", 1.5D))
                 .thenSucceed());
     }
+
+    @GameTest
+    @EmptyTemplate(value = "15x5x15", floor = true)
+    @TestHolder(description = "Tests if the pig only gets vertical knockback from explosion knockback event")
+    static void entityVerticalExplosionKnockbackEvent(final DynamicTest test) {
+        test.eventListeners().forge().addListener((final ExplosionKnockbackEvent event) -> {
+            if (event.getAffectedEntity() instanceof Pig) {
+                event.setKnockbackVelocity(new Vec3(0, event.getKnockbackVelocity().y(), 0));
+            }
+        });
+
+        test.onGameTest(helper -> helper.startSequence(() -> helper.spawnWithNoFreeWill(EntityType.PIG, 8, 3, 7))
+                .thenExecute(pig -> helper.setBlock(8, 2, 7, Blocks.ACACIA_LEAVES))
+                .thenExecute(pig -> helper.getLevel().explode(null, helper.getLevel().damageSources().generic(), null, helper.absolutePos(new BlockPos(7, 2, 7)).getCenter(), 2f, false, Level.ExplosionInteraction.BLOW))
+                .thenExecute(pig -> helper.assertEntityProperty(pig, p -> pig.getDeltaMovement().x() == 0 && pig.getDeltaMovement().y() != 0 && pig.getDeltaMovement().z() == 0, "Check explosion Knockback"))
+                .thenIdle(10)
+                .thenExecute(helper::killAllEntities)
+                .thenSucceed());
+    }
 }