power_play/src/pp_old/pp_ent.c

////////////////////////////////////////////////////////////
//~ Acquire

PP_Ent *PP_AcquireRawEnt(PP_Snapshot *ss, PP_Ent *parent, PP_EntKey key)
{
  Assert(parent->valid);
  Assert(ss->valid);
  Assert(ss == parent->ss);
  PP_Ent *ent;
  if (ss->first_free_ent > 0 && ss->first_free_ent < ss->num_ents_reserved)
  {
    /* Reuse from free list */
    ent = &ss->ents[ss->first_free_ent];
    ss->first_free_ent = ent->next_free;
  }
  else
  {
    /* Make new */
    ent = PushStructNoZero(ss->ents_arena, PP_Ent);
    ++ss->num_ents_reserved;
  }
  *ent = *PP_NilEnt();
  ent->ss = ss;
  ent->valid = 1;
  ent->owner = ss->client->player_id;
  ent->_is_xform_dirty = 1;
  ++ss->num_ents_allocated;

  PP_SetEntKey(ent, key);
  PP_Link(ent, parent);

  return ent;
}

/* Acquires a new entity that will not sync */
PP_Ent *PP_AcquireLocalEnt(PP_Ent *parent)
{
  PP_Snapshot *ss = parent->ss;
  PP_Ent *e = PP_AcquireRawEnt(ss, parent, PP_RandomKey());
  e->owner = ss->local_player;
  return e;
}

PP_Ent *PP_AcquireLocalEntWithKey(PP_Ent *parent, PP_EntKey key)
{
  PP_Snapshot *ss = parent->ss;
  PP_Ent *e = PP_AcquireRawEnt(ss, parent, key);
  e->owner = ss->local_player;
  return e;
}

/* Acquires a new entity to be synced to clients */
PP_Ent *PP_AcquireSyncSrcEnt(PP_Ent *parent)
{
  PP_Snapshot *ss = parent->ss;
  PP_Ent *e = PP_AcquireRawEnt(ss, parent, PP_RandomKey());
  PP_EnableProp(e, PP_Prop_SyncSrc);
  e->owner = ss->local_player;
  return e;
}

PP_Ent *PP_AcquireSyncSrcEntWithKey(PP_Ent *parent, PP_EntKey key)
{
  PP_Snapshot *ss = parent->ss;
  PP_Ent *e = PP_AcquireRawEnt(ss, parent, key);
  PP_EnableProp(e, PP_Prop_SyncSrc);
  e->owner = ss->local_player;
  return e;
}

/* Acquires a new entity that will sync with incoming net src ents containing key, and coming from the specified owner */
PP_Ent *PP_AcquireSyncDstEnt(PP_Ent *parent, PP_EntKey ent_id, PP_EntKey owner_id)
{
  PP_Snapshot *ss = parent->ss;
  PP_Ent *e = PP_AcquireRawEnt(ss, parent, ent_id);
  PP_EnableProp(e, PP_Prop_SyncDst);
  e->owner = owner_id;
  return e;
}

////////////////////////////////////////////////////////////
//~ Release

void PP_ReleaseRawEnt(PP_Ent *ent)
{
  PP_Snapshot *ss = ent->ss;
  /* Release children */
  PP_Ent *child = PP_EntFromKey(ss, ent->first);
  while (child->valid)
  {
    PP_Ent *next = PP_EntFromKey(ss, child->next);
    PP_ReleaseRawEnt(child);
    child = next;
  }

  /* Release uid */
  PP_SetEntKey(ent, PP_NilEntKey);

  /* Release */
  ent->valid = 0;
  ent->next_free = ss->first_free_ent;
  ss->first_free_ent = PP_IndexFromEnt(ss, ent);
  --ss->num_ents_allocated;
}

void PP_Release(PP_Ent *ent)
{
  PP_Snapshot *ss = ent->ss;
  PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
  if (parent->valid)
  {
    PP_Unlink(ent);
  }
  PP_ReleaseRawEnt(ent);
}

void PP_ReleaseAllWithProp(PP_Snapshot *ss, PP_Prop prop)
{
  TempArena scratch = BeginScratchNoConflict();

  PP_Ent **ents_to_release = PushDry(scratch.arena, PP_Ent *);
  u64 ents_to_release_count = 0;
  for (u64 ent_index = 0; ent_index < ss->num_ents_reserved; ++ent_index)
  {
    PP_Ent *ent = &ss->ents[ent_index];
    if (ent->valid && PP_HasProp(ent, prop))
    {
      *PushStructNoZero(scratch.arena, PP_Ent *) = ent;
      ++ents_to_release_count;
    }
  }

  // Release from snapshot
  //
  // TODO: Breadth first iteration to only release parent entities (since
  // child entities will be released along with parent anyway)
  for (u64 i = 0; i < ents_to_release_count; ++i)
  {
    PP_Ent *ent = ents_to_release[i];
    if (ent->valid && !ent->is_root && !PP_HasProp(ent, PP_Prop_Cmd) && !PP_HasProp(ent, PP_Prop_Player))
    {
      PP_Release(ent);
    }
  }

  EndScratch(scratch);
}

////////////////////////////////////////////////////////////
//~ Activate

void PP_ActivateEnt(PP_Ent *ent, u64 current_tick)
{
  PP_EnableProp(ent, PP_Prop_Active);
  ent->activation_tick = current_tick;
  ++ent->continuity_gen;
}

////////////////////////////////////////////////////////////
//~ Ent key

u32 PP_IndexFromEnt(PP_Snapshot *ss, PP_Ent *ent)
{
  return ent - ss->ents;
}

PP_Ent *PP_EntFromIndex(PP_Snapshot *ss, u32 index)
{
  if (index > 0 && index < ss->num_ents_reserved)
  {
    return &ss->ents[index];
  }
  else
  {
    return PP_NilEnt();
  }
}

PP_EntBin *PP_EntBinFromKey(PP_Snapshot *ss, PP_EntKey key)
{
  return &ss->key_bins[key.uid.lo % ss->num_key_bins];
}

/* NOTE: This should only really happen during ent allocation (it doesn't make sense for an allocated ent's key to change) */
void PP_SetEntKey(PP_Ent *ent, PP_EntKey key)
{
  PP_Snapshot *ss = ent->ss;
  PP_EntKey old_id = ent->key;
  if (!PP_EqEntKey(old_id, key))
  {
    /* Release old from lookup */
    if (!PP_IsNilEntKey(old_id))
    {
      PP_EntBin *bin = PP_EntBinFromKey(ss, old_id);
      u32 prev_index = 0;
      u32 next_index = 0;
      u32 search_index = bin->first;
      PP_Ent *prev = PP_NilEnt();
      PP_Ent *next = PP_NilEnt();
      PP_Ent *search = PP_EntFromIndex(ss, search_index);
      while (search->valid)
      {
        next_index = search->next_in_id_bin;
        next = PP_EntFromIndex(ss, next_index);
        if (PP_EqEntKey(search->key, old_id))
        {
          break;
        }
        prev_index = search_index;
        prev = search;
        search_index = next_index;
        search = next;
      }

      /* Old key not in bin, this should be impossible. */
      Assert(search->valid);

      if (prev->valid)
      {
        prev->next_in_id_bin = next_index;
      }
      else
      {
        bin->first = next_index;
      }

      if (next->valid)
      {
        next->prev_in_id_bin = prev_index;
      }
      else
      {
        bin->last = prev_index;
      }
    }

    /* Insert new key into lookup */
    if (!PP_IsNilEntKey(key))
    {
      if (IsRtcEnabled)
      {
        PP_Ent *existing = PP_EntFromKey(ss, key);
        /* Collision should be extremely unlikely under normal circumstances, there's probably a logic error somewhere. */
        Assert(!existing->valid);
      }

      PP_EntBin *bin = PP_EntBinFromKey(ss, key);
      u32 ent_index = PP_IndexFromEnt(ss, ent);
      PP_Ent *last = PP_EntFromIndex(ss, bin->last);
      if (last->valid)
      {
        last->next_in_id_bin = ent_index;
        ent->prev_in_id_bin = bin->last;
      }
      else
      {
        bin->first = ent_index;
        ent->prev_in_id_bin = 0;
      }
      bin->last = ent_index;
    }

    ent->key = key;
  }

}

PP_Ent *PP_EntFromKey(PP_Snapshot *ss, PP_EntKey key)
{
  PP_Ent *result = PP_NilEnt();
  if (!PP_IsNilEntKey(key) && ss->valid)
  {
    PP_EntBin *bin = PP_EntBinFromKey(ss, key);
    for (PP_Ent *e = PP_EntFromIndex(ss, bin->first); e->valid; e = PP_EntFromIndex(ss, e->next_in_id_bin))
    {
      if (PP_EqEntKey(e->key, key))
      {
        result = e;
        break;
      }
    }
  }
  return result;
}

PP_EntKey PP_RandomKey(void)
{
  PP_EntKey result = ZI;
  result.uid = UidFromTrueRand();
  return result;
}

/* Returns the deterministic key of the contact constraint ent key that should be produced from e0 & e1 colliding */
PP_EntKey PP_ContactConstraintKeyFromContactingKeys(PP_EntKey player_id, PP_EntKey id0, PP_EntKey id1)
{
  PP_EntKey result = ZI;
  result.uid = PP_ContactBasisUid;
  result.uid = CombineUid(result.uid, player_id.uid);
  result.uid = CombineUid(result.uid, id0.uid);
  result.uid = CombineUid(result.uid, id1.uid);
  return result;
}

/* Returns the deterministic key of the debug contact constraint ent key that should be produced from e0 & e1 colliding */
PP_EntKey PP_CollisionDebugKeyFromKeys(PP_EntKey player_id, PP_EntKey id0, PP_EntKey id1)
{
  PP_EntKey result = ZI;
  result.uid = PP_CollisionDebugBasisUid;
  result.uid = CombineUid(result.uid, player_id.uid);
  result.uid = CombineUid(result.uid, id0.uid);
  result.uid = CombineUid(result.uid, id1.uid);
  return result;
}

/* Returns the deterministic key of the tile chunk that should be produced at chunk pos */
PP_EntKey PP_TileChunkKeyFromIndex(Vec2I32 chunk_index)
{
  PP_EntKey result = ZI;
  result.uid = PP_TileChunkBasisUid;
  result.uid = CombineUid(result.uid, UID(RandU64FromSeed(chunk_index.x), RandU64FromSeed(chunk_index.y)));
  return result;
}

////////////////////////////////////////////////////////////
//~ Query

PP_Ent *PP_FirstWithProp(PP_Snapshot *ss, PP_Prop prop)
{
  u64 count = ss->num_ents_reserved;
  PP_Ent *entities = ss->ents;
  for (u64 ent_index = 0; ent_index < count; ++ent_index)
  {
    PP_Ent *ent = &entities[ent_index];
    if (ent->valid && PP_HasProp(ent, prop))
    {
      return ent;
    }
  }
  return PP_NilEnt();
}

PP_Ent *PP_FirstWithAllProps(PP_Snapshot *ss, PP_PropArray props)
{
  u64 count = ss->num_ents_reserved;
  PP_Ent *entities = ss->ents;
  for (u64 ent_index = 0; ent_index < count; ++ent_index)
  {
    PP_Ent *ent = &entities[ent_index];
    if (ent->valid)
    {
      b32 all = 1;
      for (u64 i = 0; i < props.count; ++i)
      {
        if (!PP_HasProp(ent, props.props[i]))
        {
          all = 0;
          break;
        }
      }
      if (all)
      {
        return ent;
      }
    }
  }
  return PP_NilEnt();
}

////////////////////////////////////////////////////////////
//~ Tree

void PP_Link(PP_Ent *ent, PP_Ent *parent)
{
  PP_Snapshot *ss = ent->ss;

  PP_Ent *old_parent = PP_EntFromKey(ss, ent->parent);
  if (old_parent->valid)
  {
    /* Unlink from current parent */
    PP_Unlink(ent);
  }

  PP_EntKey ent_id = ent->key;
  PP_EntKey last_child_id = parent->last;
  PP_Ent *last_child = PP_EntFromKey(ss, last_child_id);
  if (last_child->valid)
  {
    ent->prev = last_child_id;
    last_child->next = ent_id;
  }
  else
  {
    parent->first = ent_id;
  }
  parent->last = ent_id;

  if (parent->is_root)
  {
    ent->is_top = 1;
    ent->top = ent_id;
  }
  else
  {
    ent->top = parent->top;
  }

  ent->parent = parent->key;
}

/* NOTE: PP_Ent will be dangling after calling this, should re-link to root ent. */
void PP_Unlink(PP_Ent *ent)
{
  PP_Snapshot *ss = ent->ss;

  PP_EntKey parent_id = ent->parent;
  PP_Ent *parent = PP_EntFromKey(ss, parent_id);
  PP_Ent *prev = PP_EntFromKey(ss, ent->prev);
  PP_Ent *next = PP_EntFromKey(ss, ent->next);

  /* Unlink from parent & siblings */
  if (prev->valid)
  {
    prev->next = next->key;
  }
  else
  {
    parent->first = next->key;
  }
  if (next->valid)
  {
    next->prev = prev->key;
  }
  else
  {
    parent->last = prev->key;
  }
  ent->prev = PP_NilEntKey;
  ent->next = PP_NilEntKey;
}

////////////////////////////////////////////////////////////
//~ Xform

void PP_MarkChildXformsDirty(PP_Snapshot *ss, PP_Ent *ent)
{
  for (PP_Ent *child = PP_EntFromKey(ss, ent->first); child->valid; child = PP_EntFromKey(ss, child->next))
  {
    if (child->_is_xform_dirty)
    {
      break;
    }
    else
    {
      child->_is_xform_dirty = 1;
      PP_MarkChildXformsDirty(ss, child);
    }
  }
}

Xform PP_XformFromEnt_(PP_Snapshot *ss, PP_Ent *ent)
{
  Xform xf;
  if (ent->_is_xform_dirty)
  {
    if (ent->is_top)
    {
      xf = ent->_local_xform;
    }
    else
    {
      PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
      xf = PP_XformFromEnt_(ss, parent);
      xf = MulXform(xf, ent->_local_xform);
      ent->_xform = xf;
      ent->_is_xform_dirty = 0;
    }
    ent->_xform = xf;
    ent->_is_xform_dirty = 0;
  }
  else
  {
    xf = ent->_xform;
  }
  return xf;
}

Xform PP_XformFromEnt(PP_Ent *ent)
{
  Xform xf;
  if (ent->_is_xform_dirty)
  {
    if (ent->is_top)
    {
      xf = ent->_local_xform;
    }
    else
    {
      PP_Snapshot *ss = ent->ss;
      PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
      xf = PP_XformFromEnt_(ss, parent);
      xf = MulXform(xf, ent->_local_xform);
      ent->_xform = xf;
      ent->_is_xform_dirty = 0;
    }
    ent->_xform = xf;
    ent->_is_xform_dirty = 0;
  }
  else
  {
    xf = ent->_xform;
  }
  return xf;
}

Xform PP_LocalXformFromEnt(PP_Ent *ent)
{
  return ent->_local_xform;
}

void PP_SetXform(PP_Ent *ent, Xform xf)
{
  if (!EqXform(xf, ent->_xform))
  {
    PP_Snapshot *ss = ent->ss;
    /* Update local xform */
    if (ent->is_top)
    {
      ent->_local_xform = xf;
    }
    else
    {
      PP_Ent *parent = PP_EntFromKey(ss, ent->parent);
      Xform parent_global = PP_XformFromEnt_(ss, parent);
      ent->_local_xform = MulXform(InvertXform(parent_global), xf);
    }
    ent->_xform = xf;
    ent->_is_xform_dirty = 0;
    PP_MarkChildXformsDirty(ss, ent);
  }
}

void PP_SetLocalXform(PP_Ent *ent, Xform xf)
{
  if (!EqXform(xf, ent->_local_xform))
  {
    ent->_local_xform = xf;
    ent->_is_xform_dirty = 1;
    PP_MarkChildXformsDirty(ent->ss, ent);
  }
}

////////////////////////////////////////////////////////////
//~ Movement

void PP_SetLinearVelocity(PP_Ent *ent, Vec2 velocity)
{
  if (PP_HasProp(ent, PP_Prop_Kinematic) || PP_HasProp(ent, PP_Prop_Dynamic))
  {
    ent->linear_velocity = ClampVec2Len(velocity, SIM_MAX_LINEAR_VELOCITY);
  }
}

void PP_SetAngularVelocity(PP_Ent *ent, f32 velocity)
{
  if (PP_HasProp(ent, PP_Prop_Kinematic) || PP_HasProp(ent, PP_Prop_Dynamic))
  {
    ent->angular_velocity = ClampF32(velocity, -SIM_MAX_ANGULAR_VELOCITY, SIM_MAX_ANGULAR_VELOCITY);
  }
}

void PP_ApplyLinearImpulse(PP_Ent *ent, Vec2 impulse, Vec2 point)
{
  if (PP_HasProp(ent, PP_Prop_Dynamic))
  {
    Xform xf = PP_XformFromEnt(ent);
    Vec2 center = xf.og;
    f32 scale = AbsF32(DeterminantFromXform(xf));
    f32 inv_mass = 1.f / (ent->mass_unscaled * scale);
    f32 inv_inertia = 1.f / (ent->inertia_unscaled * scale);

    Vec2 vcp = SubVec2(point, center);
    PP_SetLinearVelocity(ent, AddVec2(ent->linear_velocity, MulVec2(impulse, inv_mass)));
    PP_SetAngularVelocity(ent, WedgeVec2(vcp, impulse) * inv_inertia);
  }
}

void PP_ApplyLinearImpulseToCenter(PP_Ent *ent, Vec2 impulse)
{
  if (PP_HasProp(ent, PP_Prop_Dynamic))
  {
    Xform xf = PP_XformFromEnt(ent);
    f32 scale = AbsF32(DeterminantFromXform(xf));
    f32 inv_mass = 1.f / (ent->mass_unscaled * scale);

    PP_SetLinearVelocity(ent, AddVec2(ent->linear_velocity, MulVec2(impulse, inv_mass)));
  }
}

void PP_ApplyForceToCenter(PP_Ent *ent, Vec2 force)
{
  if (PP_HasProp(ent, PP_Prop_Dynamic))
  {
    ent->force = AddVec2(ent->force, force);
  }
}

void PP_ApplyAngularImpulse(PP_Ent *ent, f32 impulse)
{
  if (PP_HasProp(ent, PP_Prop_Dynamic))
  {
    Xform xf = PP_XformFromEnt(ent);
    f32 scale = AbsF32(DeterminantFromXform(xf));
    f32 inv_inertia = 1.f / (ent->inertia_unscaled * scale);
    PP_SetAngularVelocity(ent, ent->angular_velocity + impulse * inv_inertia);
  }
}

void PP_ApplyTorque(PP_Ent *ent, f32 torque)
{
  if (PP_HasProp(ent, PP_Prop_Dynamic))
  {
    ent->torque += torque;
  }
}

////////////////////////////////////////////////////////////
//~ Tile

PP_Ent *PP_TileChunkFromChunkIndex(PP_Snapshot *ss, Vec2I32 chunk_index)
{
  PP_EntKey chunk_id = PP_TileChunkKeyFromIndex(chunk_index);
  PP_Ent *chunk_ent = PP_EntFromKey(ss, chunk_id);
  return chunk_ent;
}

PP_Ent *PP_TileChunkFromWorldTileIndex(PP_Snapshot *ss, Vec2I32 world_tile_index)
{
  Vec2I32 chunk_index = PP_TileChunkIndexFromWorldTileIndex(world_tile_index);
  PP_Ent *chunk_ent = PP_TileChunkFromChunkIndex(ss, chunk_index);
  return chunk_ent;
}

PP_TileKind PP_TileKindFromChunk(PP_Ent *chunk_ent, Vec2I32 local_tile_index)
{
  PP_TileKind result = chunk_ent->tile_chunk_tiles[local_tile_index.x + (local_tile_index.y * SIM_TILES_PER_CHUNK_SQRT)];
  return result;
}

////////////////////////////////////////////////////////////
//~ Lerp

void PP_LerpEnt(PP_Ent *e, PP_Ent *e0, PP_Ent *e1, f64 blend)
{
  if (PP_IsValidAndActive(e0) && PP_IsValidAndActive(e1)
  && PP_EqEntKey(e0->key, e1->key)
  && e0->continuity_gen == e1->continuity_gen)
  {
    e->_local_xform = LerpXform(e0->_local_xform, e1->_local_xform, blend);

    if (e->is_top)
    {
      /* TODO: Cache parent & child xforms in sim */
      Xform e0_xf = PP_XformFromEnt(e0);
      Xform e1_xf = PP_XformFromEnt(e1);
      PP_SetXform(e, LerpXform(e0_xf, e1_xf, blend));
    }

    e->control_force = LerpF32(e0->control_force, e1->control_force, blend);
    e->control_torque = LerpF32(e0->control_torque, e1->control_torque, blend);

    e->linear_velocity = LerpVec2(e0->linear_velocity, e1->linear_velocity, blend);
    e->angular_velocity = LerpAngleF32(e0->angular_velocity, e1->angular_velocity, blend);

    e->control.move = LerpVec2(e0->control.move, e1->control.move, blend);
    e->control.focus = LerpVec2(e0->control.focus, e1->control.focus, blend);

    e->sprite_local_xform = LerpXform(e0->sprite_local_xform, e1->sprite_local_xform, blend);
    e->animation_last_frame_change_time_ns = LerpI64(e0->animation_last_frame_change_time_ns, e1->animation_last_frame_change_time_ns, (f64)blend);
    e->animation_frame = (u32)RoundF32ToI32(LerpF32(e0->animation_frame, e1->animation_frame, blend));

    e->camera_quad_xform = LerpXform(e0->camera_quad_xform, e1->camera_quad_xform, blend);
    e->camera_xform_target = LerpXform(e0->camera_xform_target, e1->camera_xform_target, blend);
    e->shake = LerpF32(e0->shake, e1->shake, blend);

    e->tracer_gradient_start = LerpVec2(e0->tracer_gradient_start, e1->tracer_gradient_start, blend);
    e->tracer_gradient_end = LerpVec2(e0->tracer_gradient_end, e1->tracer_gradient_end, blend);
  }
}

////////////////////////////////////////////////////////////
//~ Sync

/* Walks a local & remote ent tree and allocates any missing net dst ents from remote src ents */
void PP_CreateMissingEntsFromSnapshots(PP_Ent *local_parent, PP_Ent *remote, PP_EntKey remote_player)
{
  __prof;
  if (PP_HasProp(remote, PP_Prop_SyncSrc))
  {
    PP_Snapshot *local_ss = local_parent->ss;
    PP_Snapshot *remote_ss = remote->ss;

    PP_EntKey key = remote->key;
    PP_Ent *local_ent = PP_EntFromKey(local_ss, key);
    if (!local_ent->valid)
    {
      local_ent = PP_AcquireSyncDstEnt(local_parent, key, remote_player);
    }
    for (PP_Ent *remote_child = PP_EntFromKey(remote_ss, remote->first); remote_child->valid; remote_child = PP_EntFromKey(remote_ss, remote_child->next))
    {
      PP_CreateMissingEntsFromSnapshots(local_ent, remote_child, remote_player);
    }
  }
}

/* Copies data between two synced entities */
void PP_SyncEnt(PP_Ent *local, PP_Ent *remote)
{
  PP_Ent old = *local;
  CopyStruct(local, remote);

  /* Why would 2 ents w/ different uids ever be synced? */
  Assert(PP_EqEntKey(local->key, old.key));

  local->ss = old.ss;
  local->key = old.key;

  /* Keep local tree */
  local->parent = old.parent;
  local->prev = old.prev;
  local->next = old.next;
  local->first = old.first;
  local->last = old.last;
  local->top = old.top;
  local->owner = old.owner;

  /* Keep indices */
  local->next_in_id_bin = old.next_in_id_bin;
  local->prev_in_id_bin = old.prev_in_id_bin;
  local->next_free = old.next_free;

  PP_DisableProp(local, PP_Prop_SyncSrc);
  PP_EnableProp(local, PP_Prop_SyncDst);
}

////////////////////////////////////////////////////////////
//~ Encode

void PP_EncodeEnt(BB_Writer *bw, PP_Ent *e0, PP_Ent *e1)
{
  PP_Snapshot *ss = e1->ss;
  /* FIXME: Things like xforms need to be retreived manually rather than memcopied. */

  /* TODO: Granular delta encoding */

  u64 pos = 0;
  e1->ss = e0->ss;
  while (pos < sizeof(*e1))
  {
    u64 chunk_size = MinU64(pos + 8, sizeof(*e1)) - pos;
    u8 *chunk0 = (u8 *)e0 + pos;
    u8 *chunk1 = (u8 *)e1 + pos;
    if (BB_WriteBit(bw, !EqBytes(chunk0, chunk1, chunk_size)))
    {
      u64 bits = 0;
      CopyBytes(&bits, chunk1, chunk_size);
      BB_WriteUBits(bw, bits, 64);
    }
    pos += 8;
  }
  e1->ss = ss;
}

////////////////////////////////////////////////////////////
//~ Decode

void PP_DecodeEnt(BB_Reader *br, PP_Ent *e)
{
  PP_Snapshot *old_ss = e->ss;
  {
    u64 pos = 0;
    while (pos < sizeof(*e))
    {
      u8 *chunk = (u8 *)e + pos;
      if (BB_ReadBit(br))
      {
        u64 chunk_size = MinU64(pos + 8, sizeof(*e)) - pos;
        u64 bits = BB_ReadUBits(br, 64);
        CopyBytes(chunk, &bits, chunk_size);
      }
      pos += 8;
    }
  }
  e->ss = old_ss;

}