server_knockback, locator_bar, server_dimension_players and their one-player users now end a step by the server's
game clock (a sync round trip, N ticks, a last sync) the way server_player_targets does, so a server that stalls
under load still gets all its ticks inside the step. server_knockback's frozen section waits for the stepped tick,
the stopped clock and the landed hit; dedicated_server waits for the player's leaving before /list.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Player.causeExtraKnockback pushes along Mth.sin/Mth.cos of the attacker's
yaw, which come from vanilla's 65536-entry table: facing east, the push
has no z at all. Horizon took f32 sin/cos, which left -4.4e-8 of z per
block of push (a sprinting or Knockback hit, on mobs and players).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Player.causeExtraKnockback stops the attacker's sprint on the server, and
the shared flag reaches the attacker's own client (ServerEntity sends a
player its own dirty entity data). A guest's sprint was only stopped on
the server copy for the length of the hit and never sent, so a guest (and,
on the server thread, the window) kept sprinting: every hit while
sprinting had the sprint knockback, where vanilla's needs the sprint to
start again.
- leave_guest keeps the sprint stop a guest's hit made; a guest hitting a
player stops its sprint too.
- The hub sends each guest its own shared flags (crouching, sprinting,
gliding) when they change.
- A remote client takes the sprinting bit of its own shared flags (the
flag only, as vanilla's assignValues: the speed modifier and the
wasSprinting it compares stay, so it sends START_SPRINTING again only
after it has stopped).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A guest's (and, on the server thread, the window's) knockback started from
the velocity the last hit left on its server copy, which nothing ever
slowed down, and each hit went out at once. So every hit after the first
pushed harder (0.72, then 0.76 blocks a tick where vanilla sends 0.4 each
time), netherite resisted from the wrong base, and a zombie's hit reached
the client before the friction of the tick it landed in.
Vanilla's server simulates a player too (MoveSimulationType
AUTHORITATIVE_SIDE_AND_SERVER): ServerPlayer travels every tick with no
input, and ServerEntity.sendChanges sends a velocity a hurt marked
(Entity.markHurt) as it is after that travel. A player's melee hit is the
exception (Player.causeExtraKnockback): it sends at once, then puts the
server copy back to its velocity from before the hit.
- MotionWorld::server_travel: Player.travel with no input, keeping only
the velocity (the client's moves place the player). The server's copy
checks no fall damage on its own moves (isLocalInstanceAuthoritative).
- guest_server_tick runs it last, then sends the velocity if a hurt
marked it since the last tick.
- guest_hit_by leaves a marked velocity to that; guest_struck_by (melee
from a player) sends at once and restores.
- lan_e2e `knockback`: three hits each way push the victim as far each
time.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
tools/test_server_knockback_parity.py runs vanilla's dedicated server and
Horizon's (`--dedicated --nogui`) on one flat world and joins both with two
vanilla-codec players (KnockbackClient):
- Alice hits a cow and a zombie (plain, sprinting, Knockback II, critical,
in the air); the game is frozen around the hit and stepped a tick at a
time, and the mob's Motion and Pos over 20 ticks are compared exactly;
- Alice hits Bob (the same, a shield, netherite, two hits, two sprinting
hits, a mace smash, a stronger hit inside the hurt cooldown): Bob's own
motion packets, Alice's and her sprint flag are compared;
- a zombie hits Bob twice: his motion packets.
7 of 21 cases match on main. KNOWN lists the other 14 with their causes:
the guest's server-side velocity never travels (knockback adds up from hit
to hit), the server never sends a guest its own sprint flag, the extra
knockback's direction uses f32 sin/cos instead of Mth's table, a hit in
the hurt cooldown still knocks back, and a mace smash on a player runs
none of MaceItem.hurtEnemy.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ludovic Marie