Prevent NaN velocity and crash for 0 powered explosion (#13366)

Prevents a 0 explosion_power explosion at the exact location of an entity from producing a NaN delta
due to dividing 0 by 0.
Such velocities lead to faulty client state and server crashes.

Author: sovdeeth

paper-server/patches/features/0001-Moonrise-optimisation-patches.patch

@@ -30173,7 +30173,7 @@ index 93110c815abe7baef61b1eaacfe28ebb1fc821f7..564c5064ec105a4f59476f2d21d3664b
      ChunkAccess getChunk(int x, int z, ChunkStatus chunkStatus, boolean requireChunk);
 
 diff --git a/net/minecraft/world/level/ServerExplosion.java b/net/minecraft/world/level/ServerExplosion.java
-index c132a3bfff7cf020e7fe4be616daa763b83e4b25..1c521f9f32340cf75310686c90777e521ac3ae5c 100644
+index d0286d25ea641ceb7642213067bc737175ea9d29..222ae660d2a74f708f13ba1e715bc810f433f48f 100644
 --- a/net/minecraft/world/level/ServerExplosion.java
 +++ b/net/minecraft/world/level/ServerExplosion.java
 @@ -62,6 +62,249 @@ public class ServerExplosion implements Explosion {
@@ -30576,7 +30576,7 @@ index c132a3bfff7cf020e7fe4be616daa763b83e4b25..1c521f9f32340cf75310686c90777e52
      }
 
      private void hurtEntities() {
-@@ -346,6 +628,14 @@ public class ServerExplosion implements Explosion {
+@@ -347,6 +629,14 @@ public class ServerExplosion implements Explosion {
      }
 
      public int explode() {
@@ -30591,7 +30591,7 @@ index c132a3bfff7cf020e7fe4be616daa763b83e4b25..1c521f9f32340cf75310686c90777e52
          this.level.gameEvent(this.source, GameEvent.EXPLODE, this.center);
          List<BlockPos> list = this.calculateExplodedPositions();
          this.hurtEntities();
-@@ -360,6 +650,13 @@ public class ServerExplosion implements Explosion {
+@@ -361,6 +651,13 @@ public class ServerExplosion implements Explosion {
              this.createFire(list);
          }
 
@@ -30605,7 +30605,7 @@ index c132a3bfff7cf020e7fe4be616daa763b83e4b25..1c521f9f32340cf75310686c90777e52
          return list.size();
      }
 
-@@ -449,12 +746,12 @@ public class ServerExplosion implements Explosion {
+@@ -450,12 +747,12 @@ public class ServerExplosion implements Explosion {
      // Paper start - Optimize explosions
      private float getBlockDensity(Vec3 vec3d, Entity entity) {
          if (!this.level.paperConfig().environment.optimizeExplosions) {

paper-server/patches/sources/net/minecraft/world/level/ServerExplosion.java.patch

@@ -64,7 +64,7 @@
                              }
 
                              d3 += d * 0.3F;
-@@ -176,8 +_,8 @@
+@@ -176,27 +_,64 @@
          int floor3 = Mth.floor(this.center.y + f + 1.0);
          int floor4 = Mth.floor(this.center.z - f - 1.0);
          int floor5 = Mth.floor(this.center.z + f + 1.0);
@@ -74,8 +74,9 @@
 +        for (Entity entity : list) { // Paper - used in loop
              if (!entity.ignoreExplosion(this)) {
                  double d = Math.sqrt(entity.distanceToSqr(this.center)) / f;
++                if (Double.isNaN(d)) d = Double.POSITIVE_INFINITY; // Paper - avoid infinite damage/velocity when distance and radius are 0 - +inf is chosen as 0+h / 0 is evaluated to +inf for all positive h, which distanceSqrt complies with
                  if (!(d > 1.0)) {
-@@ -185,18 +_,54 @@
+                     Vec3 vec3 = entity instanceof PrimedTnt ? entity.position() : entity.getEyePosition();
                      Vec3 vec31 = vec3.subtract(this.center).normalize();
                      boolean shouldDamageEntity = this.damageCalculator.shouldDamageEntity(this, entity);
                      float knockbackMultiplier = this.damageCalculator.getKnockbackMultiplier(entity);