P_Ctx P = Zi;
ThreadLocal P_ThreadLocalCtx P_tl = Zi;

Readonly P_Ent P_NilEnt = {
  .xf = CompXformIdentity,
  .control.look = { 1, 0 },
  .health = 1,
};

Readonly P_Constraint P_NilConstraint = {
  0
};

Readonly P_Frame P_NilFrame = {
  .first_ent = &P_NilEnt,
  .last_ent = &P_NilEnt,
};

////////////////////////////////////////////////////////////
//~ Bootstrap

void P_Bootstrap(void)
{
  P.s2v.arena = AcquireArena(Gibi(64));
}

////////////////////////////////////////////////////////////
//~ Nil helpers

b32 P_IsEntKeyNil(P_EntKey key)
{
  return key.v == 0;
}

b32 P_IsConstraintKeyNil(P_ConstraintKey key)
{
  return key.v == 0;
}

b32 P_IsEntNil(P_Ent *ent)
{
  return ent == 0 || ent == &P_NilEnt;
}

b32 P_IsConstraintNil(P_Constraint *constraint)
{
  return constraint == 0 || constraint == &P_NilConstraint;
}

b32 P_IsFrameNil(P_Frame *frame)
{
  return frame == 0 || frame == &P_NilFrame;
}

////////////////////////////////////////////////////////////
//~ Key helpers

b32 P_MatchEntKey(P_EntKey a, P_EntKey b)
{
  return a.v == b.v;
}

b32 P_MatchConstraintKey(P_ConstraintKey a, P_ConstraintKey b)
{
  return a.v == b.v;
}

P_ConstraintKey P_ConstraintKeyFromU64s(u64 a, u64 b)
{
  return (P_ConstraintKey) { .v = MixU64s(a, b) };
}

////////////////////////////////////////////////////////////
//~ Rand helpers

P_EntKey P_RandEntKey(void)
{
  // TODO: Don't use true randomness for entity keys. It's overkill & non-deterministic.
  P_EntKey result = Zi;
  TrueRand(StringFromStruct(&result));
  return result;
}

u64 P_RandU64FromEnt(P_Ent *ent)
{
  u64 result = MixU64s(ent->key.v, ent->rand_seq);
  if (!P_IsEntNil(ent))
  {
    ent->rand_seq += 1;
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ String helpers

String P_StringFromEnt(P_Ent *ent)
{
  String result = Zi;
  result.len = ent->string_len;
  result.text = ent->string_text;
  return result;
}

void P_SetEntString(P_Ent *ent, String str)
{
  i64 len = MinI64(countof(ent->string_text), str.len);
  CopyBytes(ent->string_text, str.text, len);
  ent->string_len = len;
}

////////////////////////////////////////////////////////////
//~ Tile helpers

String P_NameFromTileKind(P_TileKind kind)
{
  // Tile names array
  PERSIST Readonly String names[P_TileKind_COUNT] = {
    #define X(name, ...) [P_TileKind_##name] = CompLit(#name),
      P_TilesXList(X)
    #undef X
  };
  String result = Zi;
  if (kind >= 0 && kind < countof(names))
  {
    result = names[kind];
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Prefab helpers

String P_NameFromPrefabKind(P_PrefabKind kind)
{
  PERSIST Readonly String names[P_PrefabKind_COUNT] = {
    #define X(name, ...) [P_PrefabKind_##name] = CompLit(#name),
      P_PrefabsXList(X)
    #undef X
  };
  String result = Zi;
  if (kind >= 0 && kind < countof(names))
  {
    result = names[kind];
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Shape helpers

P_Shape P_ShapeFromDescEx(P_ShapeDesc desc)
{
  desc.count = MaxI32(desc.count, 1);
  P_Shape result = Zi;
  {
    result.points_count = desc.count;
    CopyStructs(result.points, desc.points, result.points_count);
    Vec2 accum = Zi;
    for (i32 p_idx = 0; p_idx < result.points_count; ++p_idx)
    {
      accum = AddVec2(accum, result.points[p_idx]);
    }
    result.centroid = DivVec2(accum, result.points_count);
    result.center_of_mass = result.centroid;
    result.radius = desc.radius;
    result.mass = desc.mass;
  }
  return result;
}

P_Shape P_MulXformShape(Xform xf, P_Shape shape)
{
  P_Shape result = shape;
  for (i32 i = 0; i < shape.points_count; ++i)
  {
    result.points[i] = MulXformVec2(xf, shape.points[i]);
  }
  result.centroid = MulXformVec2(xf, shape.centroid);
  result.center_of_mass = MulXformVec2(xf, shape.center_of_mass);
  return result;
}

Rng2 P_BoundingBoxFromShape(P_Shape shape)
{
  f32 skin = 0.01;
  Vec2 left = P_SupportPointFromShape(shape, VEC2(-1, 0)).p;
  Vec2 top = P_SupportPointFromShape(shape, VEC2(0, -1)).p;
  Vec2 right = P_SupportPointFromShape(shape, VEC2(1, 0)).p;
  Vec2 bottom = P_SupportPointFromShape(shape, VEC2(0, 1)).p;

  Rng2 result = Zi;
  result.p0 = VEC2(left.x - skin, top.y - skin);
  result.p1 = VEC2(right.x + skin, bottom.y + skin);
  return result;
}

P_Shape P_LocalShapeFromEnt(P_Ent *ent)
{
  P_Shape result = Zi;

  // TODO: This is a temporary hack. We should eventually switch to using a prefab lookup table.
  if (ent->is_guy)
  {
    result = P_ShapeFromDesc(
      .mass = 10,
      .count = 1,
      .radius = TweakFloat("Guy radius", 0.25, 0, 1),
    );

    // f32 guy_width = 0.75;
    // f32 guy_height = 0.4;
    // result = P_ShapeFromDesc(
    //   .mass = 10,
    //   .count = 2,
    //   .points = { VEC2(0, -guy_width / 2 + (guy_height / 2)), VEC2(0, guy_width / 2 - (guy_height / 2)) },
    //   .radius = guy_height / 2,
    // );

    // Rng2 test_rect = Zi;
    // test_rect.p0 = VEC2(-1, -1);
    // test_rect.p1 = VEC2(1, 1);
    // result = P_ShapeFromDesc(
    //   // .radius = 0.5,
    //   .radius = 0,
    //   .count = 4,
    //   .points[0] = VEC2(test_rect.p0.x, test_rect.p0.y),
    //   .points[1] = VEC2(test_rect.p1.x, test_rect.p0.y),
    //   .points[2] = VEC2(test_rect.p1.x, test_rect.p1.y),
    //   .points[3] = VEC2(test_rect.p0.x, test_rect.p1.y),
    // );
  }

  return result;
}

P_Shape P_WorldShapeFromEnt(P_Ent *ent)
{
  P_Shape local = P_LocalShapeFromEnt(ent);
  P_Shape world = P_MulXformShape(ent->xf, local);
  return world;
}

////////////////////////////////////////////////////////////
//~ Animation helpers

P_Anim P_AnimFromEnt(P_Frame *frame, P_Ent *ent)
{
  P_Anim result = Zi;
  P_Ent *wep = P_EntFromKey(frame, ent->weapon);

  // TODO: Determine animation dynamically
  i64 animation_rate_ns = NsFromSeconds(0.100);
  {
    i64 walk_duration_ns = frame->time_ns;
    result.frame_seq = walk_duration_ns / animation_rate_ns;
    // result.span = SPR_SpanKeyFromName(Lit("test"));
    result.span = SPR_SpanKeyFromName(Lit("walk"));
  }

  // TODO: Use prefab lookup

  if (ent->is_guy)
  {
    result.sheet = SPR_SheetKeyFromResource(ResourceKeyFromStore(&P_Resources, Lit("guy/guy.ase")));
  }

  if (ent->is_guy_spawn)
  {
    result.sheet = SPR_SheetKeyFromResource(ResourceKeyFromStore(&P_Resources, Lit("prefab/GuySpawn.ase")));
  }

  if (wep->is_uzi)
  {
    result.wep_sheet = SPR_SheetKeyFromResource(ResourceKeyFromStore(&P_Resources, Lit("wep/uzi.ase")));
  }

  if (wep->is_launcher)
  {
    result.wep_sheet = SPR_SheetKeyFromResource(ResourceKeyFromStore(&P_Resources, Lit("wep/launcher.ase")));
  }

  return result;
}

////////////////////////////////////////////////////////////
//~ Collision

// NOTE: Everything here is pretty much copied directly from the old prototype.
// The techniques are slow and do more than what we need. For example we should
// probably just switch from GJK to SAT for shape collision testing.

P_SupportPoint P_SupportPointFromShapeEx(P_Shape shape, Vec2 dir, i32 ignore_idx)
{
  P_SupportPoint result = Zi;
  Vec2 dir_norm = NormVec2(dir);
  f32 max_dot = -Inf;
  if (shape.points_count == 1)
  {
    // Don't ignore for single-point colliders
    ignore_idx = -1;
  }
  for (i32 point_idx = 0; point_idx < shape.points_count; ++point_idx)
  {
    if (point_idx != ignore_idx)
    {
      Vec2 p = shape.points[point_idx];
      f32 dot = DotVec2(p, dir_norm);
      if (dot > max_dot)
      {
        max_dot = dot;
        result.p = p;
        result.id = point_idx;
      }
    }
  }
  result.p = AddVec2(result.p, MulVec2(dir_norm, shape.radius));
  return result;
}

P_SupportPoint P_SupportPointFromShape(P_Shape shape, Vec2 dir)
{
  return P_SupportPointFromShapeEx(shape, dir, -1);
}

P_MenkowskiPoint P_MenkowskiPointFromShapes(P_Shape shape0, P_Shape shape1, Vec2 dir)
{
  P_MenkowskiPoint result = Zi;
  result.s0 = P_SupportPointFromShape(shape0, dir);
  result.s1 = P_SupportPointFromShape(shape1, NegVec2(dir));
  result.p = SubVec2(result.s0.p, result.s1.p);
  return result;
}

P_ClippedLine P_ClipLineToLine(Vec2 a0, Vec2 b0, Vec2 a1, Vec2 b1, Vec2 normal)
{
  Vec2 vab0 = SubVec2(b0, a0);
  Vec2 vab1 = SubVec2(b1, a1);
  Vec2 va0a1 = SubVec2(a1, a0);
  Vec2 vb0b1 = SubVec2(b1, b0);
  f32 vab0_w = WedgeVec2(vab0, normal);
  f32 vab1_w = WedgeVec2(vab1, normal);
  f32 va0a1_w = WedgeVec2(va0a1, normal);
  f32 vb0b1_w = WedgeVec2(vb0b1, normal);

  // FIXME: Handle 0 denominator
  f32 a0t;
  f32 b0t;
  {
    f32 w = 1 / vab0_w;
    a0t = ClampF32(va0a1_w * w, 0, 1);
    b0t = ClampF32(vb0b1_w * -w, 0, 1);
  }
  f32 a1t;
  f32 b1t;
  {
    f32 w = 1 / vab1_w;
    a1t = ClampF32(-va0a1_w * w, 0, 1);
    b1t = ClampF32(-vb0b1_w * -w, 0, 1);
  }

  P_ClippedLine result = Zi;
  result.a0_clipped = AddVec2(a0, MulVec2(vab0, a0t));
  result.a1_clipped = AddVec2(a1, MulVec2(vab1, a1t));
  result.b0_clipped = AddVec2(b0, MulVec2(vab0, -b0t));
  result.b1_clipped = AddVec2(b1, MulVec2(vab1, -b1t));
  return result;
}

Vec2 P_ClipPointToLine(Vec2 a, Vec2 b, Vec2 p, Vec2 normal)
{
  Vec2 vab = SubVec2(b, a);
  Vec2 vap = SubVec2(p, a);

  f32 vab_w = WedgeVec2(vab, normal);
  f32 vap_w = WedgeVec2(vap, normal);

  f32 w = 1 / vab_w;
  f32 t = ClampF32(vap_w * w, 0, 1);

  Vec2 result = AddVec2(a, MulVec2(vab, t));
  return result;
}

P_CollisionResult P_CollisionResultFromShapes(P_Shape shape0, P_Shape shape1)
{
  P_CollisionResult result = Zi;
  TempArena scratch = BeginScratchNoConflict();

  f32 tolerance = 0.05f;  // How close can non-overlapping shapes be before collision is considered
  f32 min_unique_pt_dist_sq = (0.001f * 0.001f);  // NOTE: Should always be less than tolerance, since colliding = 1 if origin is within this distance.
  u32 max_iterations = 64;  // To prevent extremely large prototypes when origin is in exact center of rounded feature

  //////////////////////////////
  //- GJK

  P_MenkowskiSimplex simplex = Zi;
  Vec2 non_overlapping_dir = Zi;
  b32 is_overlapping = 0;
  {
    P_MenkowskiPoint m = Zi;

    // First point is support point in shape's general directions to eachother
    Vec2 dir = SubVec2(shape1.centroid, shape0.centroid);
    if (IsVec2Zero(dir)) dir = VEC2(1, 0);
    simplex.a = P_MenkowskiPointFromShapes(shape0, shape1, dir);
    simplex.count = 1;

    Vec2 removed_a = Zi;
    Vec2 removed_b = Zi;
    u32 removed_count = 0;
    for (;;)
    {
      //////////////////////////////
      //- Find initial points in simplex

      if (simplex.count == 1)
      {
        // Second point is support point towards origin
        dir = NegVec2(simplex.a.p);

        m = P_MenkowskiPointFromShapes(shape0, shape1, dir);
        // Check that new point is far enough away from existing point
        if (Vec2LenSq(SubVec2(m.p, simplex.a.p)) < min_unique_pt_dist_sq)
        {
          is_overlapping = 0;
          break;
        }
        simplex.b = simplex.a;
        simplex.a = m;
        simplex.count = 2;

        // Third point is support point in direction of line normal towards origin
        dir = PerpVec2TowardsDir(SubVec2(simplex.b.p, simplex.a.p), NegVec2(simplex.a.p));
      }

      //////////////////////////////
      //- Find third point in simplex

      {
        m = P_MenkowskiPointFromShapes(shape0, shape1, dir);
        // Check that new point is far enough away from existing points
        if (
          Vec2LenSq(SubVec2(m.p, simplex.a.p)) < min_unique_pt_dist_sq ||
          Vec2LenSq(SubVec2(m.p, simplex.b.p)) < min_unique_pt_dist_sq || (
            (removed_count >= 1) && (
              (Vec2LenSq(SubVec2(m.p, removed_a)) < min_unique_pt_dist_sq) ||
              (removed_count >= 2 && Vec2LenSq(SubVec2(m.p, removed_b)) < min_unique_pt_dist_sq)
            )
          ) ||
          AbsF32(WedgeVec2(SubVec2(simplex.b.p, simplex.a.p), SubVec2(m.p, simplex.a.p))) < min_unique_pt_dist_sq
        )
        {
          is_overlapping = 0;
          break;
        }
        simplex.c = simplex.b;
        simplex.b = simplex.a;
        simplex.a = m;
        simplex.count = 3;

        if (
          (AbsF32(WedgeVec2(SubVec2(simplex.b.p, simplex.a.p), NegVec2(simplex.a.p))) <= min_unique_pt_dist_sq) ||
          (AbsF32(WedgeVec2(SubVec2(simplex.c.p, simplex.b.p), NegVec2(simplex.b.p))) <= min_unique_pt_dist_sq) ||
          (AbsF32(WedgeVec2(SubVec2(simplex.c.p, simplex.a.p), NegVec2(simplex.a.p))) <= min_unique_pt_dist_sq)
        )
        {
          // Simplex lies on origin
          is_overlapping = 1;
          break;
        }
      }

      //////////////////////////////
      //- Determine origin region

      Vec2 vab = SubVec2(simplex.b.p, simplex.a.p);
      Vec2 vac = SubVec2(simplex.c.p, simplex.a.p);
      Vec2 vbc = SubVec2(simplex.c.p, simplex.b.p);

      Vec2 rab_dir = PerpVec2TowardsDir(vab, NegVec2(vac));
      Vec2 rac_dir = PerpVec2TowardsDir(vac, NegVec2(vab));
      Vec2 rbc_dir = PerpVec2TowardsDir(vbc, vab);

      f32 rab_dot = DotVec2(rab_dir, NegVec2(simplex.a.p));
      f32 rac_dot = DotVec2(rac_dir, NegVec2(simplex.a.p));
      f32 rbc_dot = DotVec2(rbc_dir, NegVec2(simplex.b.p));

      f32 vab_dot = DotVec2(vab, NegVec2(simplex.a.p)) / Vec2LenSq(vab);
      f32 vac_dot = DotVec2(vac, NegVec2(simplex.a.p)) / Vec2LenSq(vac);
      f32 vbc_dot = DotVec2(vbc, NegVec2(simplex.b.p)) / Vec2LenSq(vbc);

      if (rab_dot >= 0 && vab_dot >= 0 && vab_dot <= 1)
      {
        // Region ab, remove c
        removed_count = 1;
        removed_a = simplex.c.p;
        simplex.count = 2;
        dir = rab_dir;  // Next third point is in direction of region ab
      }
      else if (rac_dot >= 0 && vac_dot >= 0 && vac_dot <= 1)
      {
        // Region ac, remove b
        removed_count = 1;
        removed_a = simplex.b.p;
        simplex.count = 2;
        simplex.b = simplex.c;
        dir = rac_dir;  // Next third point is in direction of region ac
      }
      else if (rbc_dot >= 0 && vbc_dot >= 0 && vbc_dot <= 1)
      {
        // Region bc, remove a
        removed_count = 1;
        removed_a = simplex.a.p;
        simplex.count = 2;
        simplex.a = simplex.b;
        simplex.b = simplex.c;
        dir = rbc_dir;  // Next third point is in direction of region bc
      }
      else if (vab_dot <= 0 && vac_dot <= 0)
      {
        // Region a, remove bc
        removed_count = 2;
        removed_a = simplex.b.p;
        removed_b = simplex.c.p;
        simplex.count = 1;
      }
      else if (vab_dot >= 1 && vbc_dot <= 0)
      {
        // Region b, remove ac
        removed_count = 2;
        removed_a = simplex.a.p;
        removed_b = simplex.c.p;
        simplex.count = 1;
        simplex.a = simplex.b;
      }
      else if (vac_dot >= 1 && vbc_dot >= 1)
      {
        // Region c, remove ab
        removed_count = 2;
        removed_a = simplex.a.p;
        removed_b = simplex.b.p;
        simplex.count = 1;
        simplex.a = simplex.c;
      }
      else
      {
        // No region, must be in simplex
        is_overlapping = 1;
        break;
      }
    }
    if (!is_overlapping)
    {
      non_overlapping_dir = dir;
    }
  }

  //////////////////////////////
  //- EPA

  // Find dir from origin to closest edge
  Vec2 normal = Zi;
  P_MenkowskiSimplex closest_feature = Zi;
  {
    P_MenkowskiPoint *proto = 0;
    if (is_overlapping)
    {
      u32 proto_count = 0;
      proto = ArenaNext(scratch.arena, P_MenkowskiPoint);
      {
        Assert(simplex.count == 3);
        P_MenkowskiPoint *tmp = PushStructsNoZero(scratch.arena, P_MenkowskiPoint, 3);
        tmp[0] = simplex.a;
        tmp[1] = simplex.b;
        tmp[2] = simplex.c;
        proto_count = 3;
      }

      i32 winding = WindingFromVec2(SubVec2(simplex.c.p, simplex.a.p), SubVec2(simplex.b.p, simplex.a.p));

      u32 epa_iterations = 0;
      for (;;)
      {
        ++epa_iterations;

        // FIXME: Winding order of ps & pe index
        P_MenkowskiPoint closest_a = Zi;
        P_MenkowskiPoint closest_b = Zi;
        u32 closest_b_index = 0;
        {
          // Find edge segment on prototype closest to the origin
          f32 closest_len_sq = Inf;
          for (u32 i = 0; i < proto_count; ++i)
          {
            u32 a_index = i;
            u32 b_index = (i < proto_count - 1) ? (i + 1) : 0;
            P_MenkowskiPoint a = proto[a_index];
            P_MenkowskiPoint b = proto[b_index];
            Vec2 vab = SubVec2(b.p, a.p);
            Vec2 vao = NegVec2(a.p);
            f32 proj_ratio = ClampF32(DotVec2(vao, vab) / Vec2LenSq(vab), 0, 1);
            Vec2 proj = AddVec2(a.p, MulVec2(vab, proj_ratio));
            f32 proj_len_sq = Vec2LenSq(proj);
            if (proj_len_sq < closest_len_sq - min_unique_pt_dist_sq)
            {
              closest_a = a;
              closest_b = b;
              closest_b_index = b_index;
              closest_len_sq = proj_len_sq;
            }
          }
        }
        Vec2 vab = SubVec2(closest_b.p, closest_a.p);

        // Find new point in dir
        Vec2 dir = MulVec2(PerpVec2(vab), winding);
        P_MenkowskiPoint m = P_MenkowskiPointFromShapes(shape0, shape1, dir);

        // Check validity of new point
        {
          b32 valid = 1;
          {
            // NOTE: Changing this value affects how stable normals are for rounded colliders
            //const f32 validity_epsilon = min_unique_pt_dist_sq;  // Arbitrary
            //const f32 validity_epsilon = 0.00000000001f;  // Arbitrary
            const f32 validity_epsilon = min_unique_pt_dist_sq;  // Arbitrary

            Vec2 vam = SubVec2(m.p, closest_a.p);
            Vec2 vbm = SubVec2(closest_b.p, closest_a.p);

            f32 dot = DotVec2(vab, vam) / Vec2LenSq(vab);

            if (dot >= -validity_epsilon && dot <= 1 - validity_epsilon && (WedgeVec2(vab, vam) * -winding) >= -validity_epsilon)
            {
              // New point is not between edge
              valid = 0;
            }
            else if (Vec2LenSq(vam) < min_unique_pt_dist_sq || Vec2LenSq(vbm) < min_unique_pt_dist_sq)
            {
              // New point is too close to existing
              valid = 0;
            }
          }

          if (!valid || epa_iterations >= max_iterations)
          {
            normal = NormVec2(dir);
            closest_feature.a = closest_a;
            closest_feature.b = closest_b;
            closest_feature.count = 2;
            break;
          }
        }

        // Expand prototype
        PushStructNoZero(scratch.arena, P_MenkowskiPoint);
        ++proto_count;

        // Shift points in prototype to make room
        for (u32 i = proto_count - 1; i > closest_b_index; --i)
        {
          u32 shift_from = (i > 0) ? i - 1 : proto_count - 1;
          u32 shift_to = i;
          proto[shift_to] = proto[shift_from];
        }

        // Insert new point into prototype
        proto[closest_b_index] = m;
      }

      // Debug draw
      // {
      //   P_DebugDrawPoint(simplex.a.p, VEC4(1, 0, 0, 0.5));
      //   P_DebugDrawPoint(simplex.b.p, VEC4(0, 1, 0, 0.5));
      //   P_DebugDrawPoint(simplex.c.p, VEC4(0, 0, 1, 0.5));
      //   P_DebugDrawLine(simplex.a.p, simplex.b.p, Color_Yellow);
      //   P_DebugDrawLine(simplex.b.p, simplex.c.p, Color_Yellow);
      //   P_DebugDrawLine(simplex.c.p, simplex.a.p, Color_Yellow);
      //   if (proto_count > 0)
      //   {
      //     for (i64 i = 0; i < proto_count; ++i)
      //     {
      //       i64 p1_idx = i + 1;
      //       if (p1_idx == proto_count)
      //       {
      //         p1_idx = 0;
      //       }
      //       Vec2 p0 = proto[i].p;
      //       Vec2 p1 = proto[p1_idx].p;
      //       P_DebugDrawLine(p0, p1, VEC4(0, 1, 0, 0.5));
      //     }
      //   }
      // }
    }
    else
    {
      normal = NormVec2(non_overlapping_dir);
      closest_feature.count = simplex.count;
      closest_feature.a = simplex.a;
      closest_feature.b = simplex.b;
    }
  }

  //////////////////////////////
  //- Determine collision

  b32 is_colliding = 0;
  {
    if (is_overlapping)
    {
      is_colliding = 1;
    }
    else
    {
      // Shapes not overlapping, determine if distance between shapes within tolerance
      if (closest_feature.count == 1)
      {
        Vec2 p = NegVec2(closest_feature.a.p);
        if (Vec2LenSq(p) <= (tolerance * tolerance))
        {
          is_colliding = 1;
        }
      }
      else
      {
        // Project origin to determine if distance is within tolerance.
        Assert(closest_feature.count == 2);
        Vec2 vab = SubVec2(closest_feature.b.p, closest_feature.a.p);
        Vec2 vao = NegVec2(closest_feature.a.p);
        f32 ratio = ClampF32(DotVec2(vab, vao) / DotVec2(vab, vab), 0, 1);
        Vec2 p = AddVec2(closest_feature.a.p, MulVec2(vab, ratio));
        if (Vec2LenSq(p) <= (tolerance * tolerance))
        {
          is_colliding = 1;
        }
      }
    }
  }

  //////////////////////////////
  //- Compute collision points

  // Clip to determine final points
  i32 collision_points_count = 0;
  P_CollisionPoint collision_points[2] = Zi;
  if (is_colliding)
  {
    // Max vertices must be < 16 to fit in 4 bit ids
    StaticAssert(countof(shape0.points) <= 16);
    {
      b32 collapse0 = 0;
      b32 collapse1 = 0;

      P_SupportPoint a0 = closest_feature.a.s0;
      P_SupportPoint a1 = closest_feature.a.s1;
      P_SupportPoint b0 = closest_feature.b.s0;
      P_SupportPoint b1 = closest_feature.b.s1;
      // FIXME: Manually account for shapes w/ 1 & 2 points
      if (closest_feature.count == 2)
      {
        if (a0.id == b0.id)
        {
          if (shape0.points_count > 1)
          {
            b0 = P_SupportPointFromShapeEx(shape0, normal, b0.id);
          }
          else
          {
            collapse0 = 1;
            b0 = a0;
          }
        }
        if (a1.id == b1.id)
        {
          if (shape1.points_count > 1)
          {
            b1 = P_SupportPointFromShapeEx(shape1, NegVec2(normal), b1.id);
          }
          else
          {
            collapse1 = 1;
            b1 = a1;
          }
        }
      }
      else
      {
        collapse0 = 1;
        collapse1 = 1;
        b0 = a0;
        b1 = a1;
      }

      Vec2 vab0 = SubVec2(b0.p, a0.p);
      Vec2 vab1 = SubVec2(b1.p, a1.p);
      Vec2 vab0_norm = NormVec2(vab0);
      Vec2 vab1_norm = NormVec2(vab1);

      // Swap points based on normal direction for consistent clipping
      if (WedgeVec2(normal, vab0) < 0)
      {
        P_SupportPoint tmp = a0;
        a0 = b0;
        b0 = tmp;
        vab0 = NegVec2(vab0);
      }
      if (WedgeVec2(normal, vab1) < 0)
      {
        P_SupportPoint tmp = a1;
        a1 = b1;
        b1 = tmp;
        vab1 = NegVec2(vab1);
      }

      // Collapse lines that are too far in the direction of the normal to be accurately clipped
      f32 collapse_epsilon = 0.05f;
      collapse0 = collapse0 || AbsF32(WedgeVec2(normal, vab0_norm)) < collapse_epsilon;
      collapse1 = collapse1 || AbsF32(WedgeVec2(normal, vab1_norm)) < collapse_epsilon;

      // Collapse lines into deepest point
      if (collapse0)
      {
        if (DotVec2(normal, vab0) > 0)
        {
          a0 = b0;
        }
        else
        {
          // TODO: Remove this (debugging)
          b0 = a0;
        }
      }
      if (collapse1)
      {
        if (DotVec2(normal, vab1) < 0)
        {
          a1 = b1;
        }
        else
        {
          // TODO: Remove this (debugging)
          b1 = a1;
        }
      }

      f32 a_sep = Inf;
      f32 b_sep = Inf;
      Vec2 a_midpoint = Zi;
      Vec2 b_midpoint = Zi;
      b32 ignore_a = 1;
      b32 ignore_b = 1;
      if (!collapse0 && !collapse1)
      {
        // Clip line to line
        P_ClippedLine clip_result = P_ClipLineToLine(a0.p, b0.p, a1.p, b1.p, normal);
        Vec2 a0_clipped = clip_result.a0_clipped;
        Vec2 a1_clipped = clip_result.a1_clipped;
        Vec2 b0_clipped = clip_result.b0_clipped;
        Vec2 b1_clipped = clip_result.b1_clipped;
        // Calc midpoint between clipped a & b
        Vec2 va0a1_clipped = SubVec2(a1_clipped, a0_clipped);
        Vec2 vb0b1_clipped = SubVec2(b1_clipped, b0_clipped);
        a_sep = DotVec2(va0a1_clipped, normal);
        b_sep = DotVec2(vb0b1_clipped, normal);
        a_midpoint = AddVec2(a0_clipped, MulVec2(va0a1_clipped, 0.5f));
        b_midpoint = AddVec2(b0_clipped, MulVec2(vb0b1_clipped, 0.5f));
        ignore_a = 0;
        ignore_b = 0;
        Vec2 vfin = SubVec2(b_midpoint, a_midpoint);
        if (Vec2LenSq(vfin) < (0.005 * 0.005))
        {
          if (a_sep > b_sep)
          {
            ignore_a = 1;
          }
          else
          {
            ignore_b = 1;
          }
        }
      }
      else
      {
        Vec2 p0 = a0.p;
        Vec2 p1 = a1.p;
        // TODO: Choose ID based on closest clipped point
        if (collapse1 && !collapse0)
        {
          // Project a1 onto vab0
          p0 = P_ClipPointToLine(a0.p, b0.p, a1.p, normal);
        }
        if (collapse0 && !collapse1)
        {
          // Project a0 onto vab1
          p1 = P_ClipPointToLine(a1.p, b1.p, a0.p, normal);
        }
        // Calc midpoint
        Vec2 vsep = SubVec2(p1, p0);
        a_midpoint = AddVec2(p0, MulVec2(vsep, 0.5f));
        a_sep = DotVec2(normal, p1) - DotVec2(normal, p0);
        ignore_a = 0;
      }

      // Insert points
      if (!ignore_a && a_sep < tolerance)
      {
        P_CollisionPoint *point = &collision_points[collision_points_count++];
        point->id = a0.id | (a1.id << 4);
        point->separation = a_sep;
        point->p = a_midpoint;
      }
      if (!ignore_b && b_sep < tolerance)
      {
        P_CollisionPoint *point = &collision_points[collision_points_count++];
        point->id = b0.id | (b1.id << 4);
        point->separation = b_sep;
        point->p = b_midpoint;
      }
    }
  }

  //////////////////////////////
  //- Compute closest points

  Vec2 closest_p0 = Zi;
  Vec2 closest_p1 = Zi;
  if (closest_feature.count == 1)
  {
    closest_p0 = closest_feature.a.s0.p;
    closest_p1 = closest_feature.a.s1.p;
  }
  else
  {
    Assert(closest_feature.count == 2);
    // FIXME: Winding order dependent?
    f32 ratio = 0;
    {
      // Determine ratio between edge a & b that projected origin lies
      Vec2 vab = SubVec2(closest_feature.b.p, closest_feature.a.p);
      Vec2 vao = NegVec2(closest_feature.a.p);
      ratio = ClampF32(DotVec2(vab, vao) / DotVec2(vab, vab), 0, 1);
    }
    // Shape 0
    closest_p0 = SubVec2(closest_feature.b.s0.p, closest_feature.a.s0.p);
    closest_p0 = MulVec2(closest_p0, ratio);
    closest_p0 = AddVec2(closest_p0, closest_feature.a.s0.p);
    // Shape 1
    closest_p1 = SubVec2(closest_feature.b.s1.p, closest_feature.a.s1.p);
    closest_p1 = MulVec2(closest_p1, ratio);
    closest_p1 = AddVec2(closest_p1, closest_feature.a.s1.p);
  }

  CopyStructs(result.collision_points, collision_points, countof(collision_points));
  result.collision_points_count = collision_points_count;
  result.collision_normal = normal;
  result.closest_p0 = closest_p0;
  result.closest_p1 = closest_p1;

  EndScratch(scratch);
  return result;
}

P_RaycastResult P_RaycastShape(P_Shape shape, Vec2 ray_start, Vec2 ray_dir)
{
  f32 radius = shape.radius;

  f32 ray_len = Vec2Len(ray_dir);
  Vec2 ray_dir_norm = DivVec2(ray_dir, ray_len);

  Vec2 s = ray_start;
  Vec2 e = AddVec2(ray_start, ray_dir_norm);
  Vec2 vse = ray_dir_norm;

  Vec2 isect = Zi;
  Vec2 isect_normal = Zi;
  b32 isect_is_round = 0;
  b32 isect_found = 0;
  if (shape.points_count > 1)
  {
    // Find expanded line intersections with ray
    for (i32 p_idx = 0; p_idx < shape.points_count && !isect_found; ++p_idx)
    {
      Vec2 a = Zi;
      Vec2 b = Zi;
      Vec2 vab = Zi;
      Vec2 normal = Zi;
      {
        i32 a_idx = p_idx;
        i32 b_idx = a_idx + 1;
        if (b_idx >= shape.points_count)
        {
          b_idx = 0;
        }

        Vec2 a_orig = shape.points[a_idx];
        Vec2 b_orig = shape.points[b_idx];
        vab = SubVec2(b_orig, a_orig);
        normal = NegVec2(PerpVec2(NormVec2(vab)));
        Vec2 radius_add = MulVec2(normal, radius);

        a = AddVec2(a_orig, radius_add);
        b = AddVec2(b_orig, radius_add);
      }
      Vec2 vsa = SubVec2(a, s);
      Vec2 vsb = SubVec2(b, s);
      f32 wa = WedgeVec2(vse, vsa);
      f32 wb = WedgeVec2(vse, vsb);
      if (wa > 0 && wb < 0)
      {
        f32 t = -wa / (wb - wa);
        isect = AddVec2(a, MulVec2(vab, t));
        isect_normal = normal;
        isect_found = 1;
      }
    }

    // Find closest rounded corner
    if (!isect_found && radius != 0)
    {
      isect_is_round = 1;
      for (i32 f_idx = 0; f_idx < shape.points_count && !isect_found; ++f_idx)
      {
        Vec2 f_orig = shape.points[f_idx];
        Vec2 a = Zi;
        Vec2 b = Zi;
        Vec2 vab = Zi;
        {
          i32 prev_idx = f_idx - 1;
          i32 next_idx = f_idx + 1;
          if (prev_idx < 0)
          {
            prev_idx = shape.points_count - 1;
          }
          if (next_idx >= shape.points_count)
          {
            next_idx = 0;
          }
          Vec2 prev_orig = shape.points[prev_idx];
          Vec2 next_orig = shape.points[next_idx];
          Vec2 vpf = SubVec2(f_orig, prev_orig);
          Vec2 vfn = SubVec2(next_orig, f_orig);
          Vec2 vpf_norm = NormVec2(vpf);
          Vec2 vfn_norm = NormVec2(vfn);
          Vec2 radius_add_a = MulVec2(PerpVec2(vpf_norm), -radius);
          Vec2 radius_add_b = MulVec2(PerpVec2(vfn_norm), -radius);
          a = AddVec2(f_orig, radius_add_a);
          b = AddVec2(f_orig, radius_add_b);
        }
        Vec2 vsa = SubVec2(a, s);
        Vec2 vsb = SubVec2(b, s);
        f32 wa = WedgeVec2(vse, vsa);
        f32 wb = WedgeVec2(vse, vsb);
        if (wa > 0 && wb < 0)
        {
          isect = f_orig;
          isect_found = 1;
        }
      }
    }

    // Find closest corner
    if (!isect_found)
    {
      f32 min_dist = Inf;
      for (i32 p_idx = 0; p_idx < shape.points_count && !isect_found; ++p_idx)
      {
        Vec2 p = shape.points[p_idx];
        f32 dist = AbsF32(WedgeVec2(vse, SubVec2(p, s)));
        if (dist < min_dist)
        {
          isect = p;
          min_dist = dist;
        }
      }
    }
  }
  else if (shape.points_count == 1 && radius != 0)
  {
    isect = shape.points[0];
    isect_is_round = 1;
  }


  // Find round intersection
  b32 is_intersecting = 0;
  if (isect_is_round || !isect_found)
  {
    Vec2 vsi = SubVec2(isect, s);

    f32 dot = DotVec2(vse, vsi);
    f32 wedge = WedgeVec2(vse, vsi);

    is_intersecting = AbsF32(wedge) < radius;
    if (is_intersecting)
    {
      f32 diff = SqrtF32(radius * radius - wedge * wedge);
      f32 entrance_t = dot - diff;
      f32 exit_t = dot + diff;
      {
        Vec2 old_isect = isect;
        isect = AddVec2(s, MulVec2(vse, entrance_t));
        isect_normal = NormVec2(SubVec2(isect, old_isect));
      }
    }
  }
  else
  {
    is_intersecting = isect_found;
  }

  P_RaycastResult result = Zi;
  result.is_intersecting = is_intersecting;
  if (is_intersecting)
  {
    result.p = isect;
    result.normal = isect_normal;
  }

  return result;
}

Vec2 P_EdgePointFromShape(P_Shape shape, Vec2 dir)
{
  Vec2 result = shape.centroid;
  P_RaycastResult raycast = P_RaycastShape(shape, shape.centroid, NegVec2(dir));
  if (raycast.is_intersecting)
  {
    result = raycast.p;
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Lookup helpers

P_Ent *P_EntFromKey(P_Frame *frame, P_EntKey key)
{
  P_Ent *result = &P_NilEnt;
  P_World *world = frame->world;
  if (!P_IsEntKeyNil(key) && frame->tick > 0 && frame->ents_count > 0 && frame->ent_bins_count > 0)
  {
    i64 tick = frame->tick;
    P_EntBin *bin = &frame->ent_bins[key.v % frame->ent_bins_count];
    for (P_Ent *e = bin->first; e; e = e->next_in_bin)
    {
      if (e->key.v == key.v)
      {
        result = e;
        break;
      }
    }
  }
  return result;
}

P_Ent *P_SourcePlayerFromEnt(P_Frame *frame, P_Ent *ent)
{
  P_Ent *result = ent;
  while (!P_IsEntNil(result) && !result->is_player)
  {
    result = P_EntFromKey(frame, result->source);
  }
  return result;
}

P_Constraint *P_ConstraintFromKey(P_Frame *frame, P_ConstraintKey key)
{
  P_Constraint *result = &P_NilConstraint;
  P_World *world = frame->world;
  if (!P_IsConstraintKeyNil(key) && frame->tick > 0 && frame->constraints_count > 0 && frame->constraint_bins_count > 0)
  {
    i64 tick = frame->tick;
    P_ConstraintBin *bin = &frame->constraint_bins[key.v % frame->constraint_bins_count];
    for (P_Constraint *c = bin->first; c; c = c->next_in_bin)
    {
      if (c->key.v == key.v)
      {
        result = c;
        break;
      }
    }
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Iteration helpers

P_Ent *P_FirstEnt(P_Frame *frame)
{
  P_Ent *result = &P_NilEnt;
  if (!P_IsEntNil(frame->first_ent))
  {
    result = frame->first_ent;
  }
  return result;
}

P_Ent *P_NextEnt(P_Ent *e)
{
  P_Ent *result = &P_NilEnt;
  if (!P_IsEntNil(e) && !P_IsEntNil(e->next))
  {
    result = e->next;
  }
  return result;
}

P_Constraint *P_FirstConstraint(P_Frame *frame)
{
  P_Constraint *result = &P_NilConstraint;
  if (!P_IsConstraintNil(frame->first_constraint))
  {
    result = frame->first_constraint;
  }
  return result;
}

P_Constraint *P_NextConstraint(P_Constraint *c)
{
  P_Constraint *result = &P_NilConstraint;
  if (!P_IsConstraintNil(c) && !P_IsConstraintNil(c->next))
  {
    result = c->next;
  }
  return result;
}

////////////////////////////////////////////////////////////
//~ Space

P_Space P_SpaceFromEnts(Arena *arena, P_Frame *frame)
{
  P_Space space = Zi;
  TempArena scratch = BeginScratch(arena);
  P_World *world = frame->world;
  space.dims = VEC2I32(P_WorldPitch, P_WorldPitch);
  i64 cells_count = P_WorldPitch * P_WorldPitch;
  space.cells = PushStructs(arena, P_SpaceCell, cells_count);

  Rng2 space_aabb = RNG2(
    VEC2(0, 0),
    VEC2(P_WorldPitch, P_WorldPitch)
  );

  //- Insert entity shapes
  for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
  {
    b32 should_insert = ent->is_guy;
    if (should_insert)
    {
      P_Shape shape = P_WorldShapeFromEnt(ent);
      Rng2 aabb = P_BoundingBoxFromShape(shape);
      aabb = AddRng2Vec2(aabb, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));
      aabb.p0 = FloorVec2(aabb.p0);
      aabb.p1 = CeilVec2(aabb.p1);
      aabb.p1.x = MaxF32(aabb.p1.x, aabb.p0.x + 1);
      aabb.p1.y = MaxF32(aabb.p1.y, aabb.p0.y + 1);
      aabb = IntersectRng2(aabb, space_aabb);
      if (!IsRng2Empty(aabb))
      {
        ++space.unique_entries_count;
        for (i32 y = aabb.p0.y; y < aabb.p1.y; ++y)
        {
          for (i32 x = aabb.p0.x; x < aabb.p1.x; ++x)
          {
            i64 cell_idx = y * P_WorldPitch + x;
            P_SpaceCell *cell = &space.cells[cell_idx];
            P_SpaceEntryNode *entry_node = PushStruct(arena, P_SpaceEntryNode);
            SllStackPush(cell->first, entry_node);
            entry_node->entry.shape = shape;
            entry_node->entry.shape_id = ent->key.v;
            ++space.entries_count;
          }
        }
      }
    }
  }

  EndScratch(scratch);
  return space;
}

P_Space P_SpaceFromWalls(Arena *arena, P_Frame *frame)
{
  P_Space space = Zi;
  TempArena scratch = BeginScratch(arena);
  P_World *world = frame->world;
  space.dims = VEC2I32(P_WorldPitch, P_WorldPitch);
  i64 cells_count = P_WorldPitch * P_WorldPitch;
  space.cells = PushStructs(arena, P_SpaceCell, cells_count);

  Rng2 space_aabb = RNG2(
    VEC2(0, 0),
    VEC2(P_WorldPitch, P_WorldPitch)
  );

  Enum(WallDir)
  {
    WallDir_None,
    WallDir_Up,
    WallDir_Right,
    WallDir_Down,
    WallDir_Left,
  };

  Struct(GenWall)
  {
    GenWall *next;
    WallDir dir;
    Vec2I32 start;
    Vec2I32 end;
  };

  GenWall *first_wall = 0;

  //- Generate horizontal walls
  for (i32 tile_y = 0; tile_y < P_TilesPitch + 1; ++tile_y)
  {
    i32 wall_start = -1;
    WallDir prev_wall_dir = WallDir_None;
    for (i32 tile_x = 0; tile_x < P_TilesPitch + 1; ++tile_x)
    {
      P_TileKind tile = P_TileKind_Empty;
      P_TileKind tile_t = P_TileKind_Empty;
      if (tile_x >= 0 && tile_x < P_TilesPitch)
      {
        if (tile_y >= 0 && tile_y < P_TilesPitch)
        {
          tile = world->tiles[tile_y * (i32)P_TilesPitch + tile_x];
        }
        if ((tile_y - 1) >= 0 && (tile_y - 1) < P_TilesPitch)
        {
          tile_t = world->tiles[(tile_y - 1) * (i32)P_TilesPitch + tile_x];
        }
      }
      WallDir dir = WallDir_None;
      if (tile == P_TileKind_Wall && tile_t != P_TileKind_Wall)
      {
        dir = WallDir_Up;
      }
      else if (tile != P_TileKind_Wall && tile_t == P_TileKind_Wall)
      {
        dir = WallDir_Down;
      }
      if (dir != prev_wall_dir)
      {
        if (prev_wall_dir != WallDir_None)
        {
          GenWall *wall = PushStruct(scratch.arena, GenWall);
          SllStackPush(first_wall, wall);
          wall->dir = prev_wall_dir;
          wall->start = VEC2I32(wall_start, tile_y);
          wall->end = VEC2I32(tile_x, tile_y);
        }
        wall_start = tile_x;
      }
      prev_wall_dir = dir;
    }
  }

  //- Generate vertical walls
  for (i32 tile_x = 0; tile_x < P_TilesPitch + 1; ++tile_x)
  {
    i32 wall_start = -1;
    WallDir prev_wall_dir = WallDir_None;
    for (i32 tile_y = 0; tile_y < P_TilesPitch + 1; ++tile_y)
    {
      P_TileKind tile = P_TileKind_Empty;
      P_TileKind tile_l = P_TileKind_Empty;
      if (tile_y >= 0 && tile_y < P_TilesPitch)
      {
        if (tile_x >= 0 && tile_x < P_TilesPitch)
        {
          tile = world->tiles[tile_y * (i32)P_TilesPitch + tile_x];
        }
        if ((tile_x - 1) >= 0 && (tile_x - 1) < P_TilesPitch)
        {
          tile_l = world->tiles[tile_y * (i32)P_TilesPitch + (tile_x - 1)];
        }
      }
      WallDir dir = WallDir_None;
      if (tile == P_TileKind_Wall && tile_l != P_TileKind_Wall)
      {
        dir = WallDir_Left;
      }
      else if (tile != P_TileKind_Wall && tile_l == P_TileKind_Wall)
      {
        dir = WallDir_Right;
      }
      if (dir != prev_wall_dir)
      {
        if (prev_wall_dir != WallDir_None)
        {
          GenWall *wall = PushStruct(scratch.arena, GenWall);
          SllStackPush(first_wall, wall);
          wall->dir = prev_wall_dir;
          wall->start = VEC2I32(tile_x, wall_start);
          wall->end = VEC2I32(tile_x, tile_y);
        }
        wall_start = tile_y;
      }
      prev_wall_dir = dir;
    }
  }

  //- Push walls to space
  for (GenWall *wall = first_wall; wall; wall = wall->next)
  {
    Vec2 p0 = VEC2(wall->start.x / P_TilesPerMeter - P_WorldPitch / 2, wall->start.y / P_TilesPerMeter - P_WorldPitch / 2);
    Vec2 p1 = VEC2(wall->end.x / P_TilesPerMeter - P_WorldPitch / 2, wall->end.y / P_TilesPerMeter - P_WorldPitch / 2);
    // P_Shape shape = P_ShapeFromDesc(.count = 2, .points = { p0, p1 }, .radius = 0.01 );
    P_Shape shape = P_ShapeFromDesc(.count = 2, .points = { p0, p1 }, .radius = 0.0 );
    Rng2 aabb = P_BoundingBoxFromShape(shape);
    aabb = AddRng2Vec2(aabb, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));
    aabb.p0 = FloorVec2(aabb.p0);
    aabb.p1 = CeilVec2(aabb.p1);
    aabb.p1.x = MaxF32(aabb.p1.x, aabb.p0.x + 1);
    aabb.p1.y = MaxF32(aabb.p1.y, aabb.p0.y + 1);
    aabb = IntersectRng2(aabb, space_aabb);
    u64 id = P_WallShapeIDBasis ^ wall->dir;
    id = MixU64s(id, (((u64)wall->start.x) | ((u64)wall->start.y << 32)));
    id = MixU64s(id, (((u64)wall->end.x) | ((u64)wall->end.y << 32)));

    ++space.unique_entries_count;
    for (i32 y = aabb.p0.y; y < aabb.p1.y; ++y)
    {
      for (i32 x = aabb.p0.x; x < aabb.p1.x; ++x)
      {
        i64 cell_idx = y * P_WorldPitch + x;
        P_SpaceCell *cell = &space.cells[cell_idx];
        P_SpaceEntryNode *entry_node = PushStruct(arena, P_SpaceEntryNode);
        SllStackPush(cell->first, entry_node);
        entry_node->entry.shape = shape;
        entry_node->entry.shape_id = id;
        entry_node->entry.dir.x = (wall->dir == WallDir_Right) + ((wall->dir == WallDir_Left) * -1);
        entry_node->entry.dir.y = (wall->dir == WallDir_Down) + ((wall->dir == WallDir_Up) * -1);
        ++space.entries_count;
      }
    }
  }

  EndScratch(scratch);
  return space;
}

P_SpaceCell P_SpaceCellFromPos(P_Space *space, Vec2 pos)
{
  P_SpaceCell result = Zi;
  pos = AddVec2(pos, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));
  if (pos.x >= 0 && pos.x < space->dims.x && pos.y >= 0 && pos.y < space->dims.y)
  {
    i64 cell_idx = FloorF32(pos.y) * P_WorldPitch + FloorF32(pos.x);
    result = space->cells[cell_idx];
  }
  return result;
}

// TODO: Parameterized bin-count
void P_UniqueSpaceEntriesFromRay(Arena *arena, P_SpaceEntryList *result, i32 spaces_count, P_Space **spaces, Vec2 ray_p0, Vec2 ray_p1)
{
  TempArena scratch = BeginScratch(arena);
  {
    Struct(BinEntry) { BinEntry *next; u64 shape_id; };
    u64 bins_count = 256;
    BinEntry **bins = PushStructs(scratch.arena, BinEntry *, bins_count);

    P_DebugDrawLine(ray_p0, ray_p1, Color_Red);

    // TODO: Clip to avoid unnecessary iterations outside of world bounds
    ray_p0 = AddVec2(ray_p0, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));
    ray_p1 = AddVec2(ray_p1, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));

    Vec2I32 dda_start = Vec2I32FromVec(FloorVec2(ray_p0));
    Vec2I32 dda_end = Vec2I32FromVec(FloorVec2(ray_p1));

    Vec2 delta = SubVec2(ray_p1, ray_p0);
    Vec2 inv_delta = RecipVec2(delta);
    Vec2 step_dir = VEC2((delta.x > 0) - (delta.x < 0), (delta.y > 0) - (delta.y < 0));
    Vec2 t_delta = MulVec2Vec2(step_dir, inv_delta);
    Vec2 t_max = SubVec2(Vec2FromVec(dda_start), ray_p0);
    t_max.x += step_dir.x > 0;
    t_max.y += step_dir.y > 0;
    t_max = MulVec2Vec2(t_max, inv_delta);

    Vec2I32 dda_pos = dda_start;
    b32 done = 0;
    while (!done)
    {
      if (dda_pos.x >= 0 && dda_pos.y >= 0 && dda_pos.x < P_WorldPitch && dda_pos.y < P_WorldPitch)
      {
        if (P_tl.debug_draw_enabled)
        {
          Vec2 world_pos = Vec2FromVec(dda_pos);
          world_pos = SubVec2(world_pos, VEC2(P_WorldPitch / 2.0, P_WorldPitch / 2.0));
          P_DebugDrawRect(RNG2(world_pos, AddVec2(world_pos, VEC2(1, 1))), VEC4(0.85, 0.5, 0.75, 0.75));
        }
        for (i32 space_idx = 0; space_idx < spaces_count; ++space_idx)
        {
          P_Space *space = spaces[space_idx];
          if (dda_pos.x < space->dims.x && dda_pos.y < space->dims.y)
          {
            i64 cell_idx = dda_pos.y * P_WorldPitch + dda_pos.x;
            P_SpaceCell cell = space->cells[cell_idx];
            for (
              P_SpaceEntryNode *src_space_entry_node = cell.first;
              src_space_entry_node;
              src_space_entry_node = src_space_entry_node->next
            )
            {
              P_SpaceEntry *src_space_entry = &src_space_entry_node->entry;
              BinEntry **bin = &bins[src_space_entry->shape_id % bins_count];
              BinEntry *bin_entry = *bin;
              for (; bin_entry; bin_entry = bin_entry->next)
              {
                if (bin_entry->shape_id == src_space_entry->shape_id)
                {
                  break;
                }
              }
              if (!bin_entry)
              {
                // Entry is unique
                {
                  bin_entry = PushStruct(scratch.arena, BinEntry);
                  bin_entry->shape_id = src_space_entry->shape_id;
                  SllStackPush(*bin, bin_entry);
                }
                {
                  P_SpaceEntryNode *dst = PushStruct(arena, P_SpaceEntryNode);
                  dst->entry = *src_space_entry;
                  SllQueuePush(result->first, result->last, dst);
                  ++result->count;
                }
              }
            }
          }
        }
      }
      if (dda_pos.x == dda_end.x && dda_pos.y == dda_end.y)
      {
        done = 1;
      }
      else if (t_max.x < t_max.y)
      {
        dda_pos.x += step_dir.x;
        t_max.x += t_delta.x;
      }
      else
      {
        dda_pos.y += step_dir.y;
        t_max.y += t_delta.y;
      }
    }
  }
  EndScratch(scratch);
}

////////////////////////////////////////////////////////////
//~ List helpers

P_Ent *P_PushTempEnt(Arena *arena, P_EntList *list)
{
  P_EntListNode *n = PushStruct(arena, P_EntListNode);
  SllQueuePush(list->first, list->last, n);
  ++list->count;
  P_Ent *ent = &n->ent;
  *ent = P_NilEnt;
  ent->exists = 1;
  return ent;
}

////////////////////////////////////////////////////////////
//~ Debug draw

void P_DebugDrawPoint(Vec2 p, Vec4 srgb)
{
  if (P_tl.debug_draw_enabled)
  {
    P_DebugDrawNode *n = PushStruct(P_tl.debug_arena, P_DebugDrawNode);
    {
      n->kind = P_DebugDrawKind_Point;
      n->srgb32 = U32FromVec4(srgb);
      n->point.p = p;
    }
    SllQueuePush(P_tl.first_debug_draw_node, P_tl.last_debug_draw_node, n);
    P_tl.debug_draw_nodes_count += 1;
  }
}

void P_DebugDrawLine(Vec2 p0, Vec2 p1, Vec4 srgb)
{
  if (P_tl.debug_draw_enabled)
  {
    P_DebugDrawNode *n = PushStruct(P_tl.debug_arena, P_DebugDrawNode);
    {
      n->kind = P_DebugDrawKind_Line;
      n->srgb32 = U32FromVec4(srgb);
      n->line.p0 = p0;
      n->line.p1 = p1;
    }
    SllQueuePush(P_tl.first_debug_draw_node, P_tl.last_debug_draw_node, n);
    P_tl.debug_draw_nodes_count += 1;
  }
}

void P_DebugDrawRect(Rng2 rect, Vec4 srgb)
{
  if (P_tl.debug_draw_enabled)
  {
    P_DebugDrawNode *n = PushStruct(P_tl.debug_arena, P_DebugDrawNode);
    {
      n->kind = P_DebugDrawKind_Rect;
      n->srgb32 = U32FromVec4(srgb);
      n->rect = rect;
    }
    SllQueuePush(P_tl.first_debug_draw_node, P_tl.last_debug_draw_node, n);
    P_tl.debug_draw_nodes_count += 1;
  }
}

void P_DebugDrawShape(P_Shape shape, Vec4 srgb)
{
  if (P_tl.debug_draw_enabled)
  {
    P_DebugDrawNode *n = PushStruct(P_tl.debug_arena, P_DebugDrawNode);
    {
      n->kind = P_DebugDrawKind_Shape;
      n->srgb32 = U32FromVec4(srgb);
      n->shape = shape;
    }
    SllQueuePush(P_tl.first_debug_draw_node, P_tl.last_debug_draw_node, n);
    P_tl.debug_draw_nodes_count += 1;
  }
}


void P_DebugDrawFrame(P_Frame *frame)
{
  if (P_tl.debug_draw_enabled)
  {
    P_World *world = frame->world;

    //////////////////////////////
    //- Draw walls

    {
      TempArena scratch = BeginScratchNoConflict();
      {
        Struct(BinEntry) { BinEntry *next; u64 shape_id; };
        u64 bins_count = NextPow2U64(world->walls_space.unique_entries_count * 4);
        BinEntry **bins = PushStructs(scratch.arena, BinEntry *, bins_count);

        i64 cells_count = world->walls_space.dims.x * world->walls_space.dims.y;
        for (i64 cell_idx = 0; cell_idx < cells_count; ++cell_idx)
        {
          P_SpaceCell *cell = &world->walls_space.cells[cell_idx];
          for (P_SpaceEntryNode *space_entry_node = cell->first; space_entry_node; space_entry_node = space_entry_node->next)
          {
            P_SpaceEntry *space_entry = &space_entry_node->entry;
            BinEntry **bin = &bins[space_entry->shape_id % bins_count];
            BinEntry *bin_entry = *bin;
            for (; bin_entry; bin_entry = bin_entry->next)
            {
              if (bin_entry->shape_id == space_entry->shape_id)
              {
                break;
              }
            }
            if (!bin_entry)
            {
              // Draw unique wall
              {
                bin_entry = PushStruct(scratch.arena, BinEntry);
                bin_entry->shape_id = space_entry->shape_id;
                SllStackPush(*bin, bin_entry);
              }
              {
                Vec4 color = VEC4(0.5, 0.75, 0.5, 0.75);
                P_DebugDrawShape(space_entry->shape, color);
              }
            }
          }
        }
      }
      EndScratch(scratch);
    }

    for (i32 cell_y = 0; cell_y < world->walls_space.dims.y; ++cell_y)
    {
      for (i32 cell_x = 0; cell_x < world->walls_space.dims.x; ++cell_x)
      {
      }
    }

    //////////////////////////////
    //- Draw entities

    for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
    {
      P_Shape world_shape = P_WorldShapeFromEnt(ent);

      // Draw aabb
      {
        Vec4 color = VEC4(0.4, 0.2, 0.2, 1);
        Rng2 bb = P_BoundingBoxFromShape(world_shape);
        P_DebugDrawRect(bb, color);
      }

      // Draw shape
      {
        // Vec4 color = Color_Cyan;
        // Vec4 color = VEC4(0.2, 0.4, 0.2, 1);
        Vec4 color = MulVec4Vec4(VEC4(1, 1, 1, 1), P_tl.debug_tint);
        P_DebugDrawShape(world_shape, color);
      }

      // Draw rot
      {
        Vec4 color = VEC4(0.8, 0.8, 0.8, 1);
        Vec2 p0 = world_shape.centroid;
        Vec2 p1 = P_EdgePointFromShape(world_shape, ent->xf.r);
        P_DebugDrawLine(p0, p1, color);
      }

      // Draw look
      {
        Vec4 color = VEC4(0.4, 0.8, 0.4, 1);
        Vec2 p0 = world_shape.centroid;
        Vec2 p1 = P_EdgePointFromShape(world_shape, ent->control.look);
        P_DebugDrawLine(p0, p1, color);
      }
    }

    //////////////////////////////
    //- Draw constraints

    for (P_Constraint *constraint = P_FirstConstraint(frame); !P_IsConstraintNil(constraint); constraint = P_NextConstraint(constraint))
    {
      P_Ent *ent0 = P_EntFromKey(frame, constraint->ent0);
      P_Ent *ent1 = P_EntFromKey(frame, constraint->ent1);
      Vec2 normal = constraint->normal;
      Vec2 center0 = constraint->static_center0;
      Vec2 center1 = constraint->static_center1;
      if (!P_IsEntNil(ent0))
      {
        center0 = P_WorldShapeFromEnt(ent0).center_of_mass;
      }
      if (!P_IsEntNil(ent1))
      {
        center1 = P_WorldShapeFromEnt(ent1).center_of_mass;
      }

      for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
      {
        P_ContactPoint *contact = &constraint->points[contact_idx];
        Vec2 p0 = AddVec2(center0, contact->vcp0);
        Vec2 p1 = AddVec2(center1, contact->vcp1);
        P_DebugDrawPoint(p0, Color_Cyan);
        P_DebugDrawLine(p0, AddVec2(p0, normal), Color_White);
      }
    }
  }
}

////////////////////////////////////////////////////////////
//~ Msg

P_Msg *P_PushMsg(P_MsgKind kind, String data)
{
  P_MsgNode *msg_node = PushStruct(P_tl.out_msgs_arena, P_MsgNode);
  P_Msg *msg = &msg_node->msg;
  msg->kind = kind;
  msg->data = PushString(P_tl.out_msgs_arena, data);
  msg->xf = XformIdentity;
  DllQueuePush(P_tl.out_msgs.first, P_tl.out_msgs.last, msg_node);
  ++P_tl.out_msgs.count;
  return msg;
}

////////////////////////////////////////////////////////////
//~ World

P_World *P_AcquireWorld(void)
{
  P_World *world = 0;
  {
    Arena *arena = AcquireArena(Gibi(64));
    world = PushStruct(arena, P_World);
    world->arena = arena;
  }
  world->frames_arena = AcquireArena(Gibi(64));
  world->bake_arena = AcquireArena(Gibi(64));

  world->first_frame = &P_NilFrame;
  world->last_frame = &P_NilFrame;
  world->frame_bins_count = Kibi(16);
  world->frame_bins = PushStructs(world->arena, P_FrameBin, world->frame_bins_count);

  // TODO

  world->tiles = PushStructs(world->arena, u8, P_TilesCount);

  TrueRand(StringFromStruct(&world->seed));
  return world;
}

void P_SpawnEntsFromList(P_Frame *frame, P_EntList ents)
{
  P_World *world = frame->world;
  for (P_EntListNode *n = ents.first; n; n = n->next)
  {
    P_Ent *src = &n->ent;
    P_EntKey key = src->key;
    if (!P_IsEntKeyNil(src->key))
    {
      P_EntBin *bin = &frame->ent_bins[key.v % frame->ent_bins_count];
      P_Ent *dst = bin->first;
      for (; dst; dst = dst->next_in_bin)
      {
        if (dst->key.v == key.v)
        {
          break;
        }
      }
      if (!dst)
      {
        dst = world->first_free_ent;
        if (dst)
        {
          SllStackPop(world->first_free_ent);
        }
        else
        {
          dst = PushStructNoZero(world->frames_arena, P_Ent);
        }
        DllQueuePushNPZ(&P_NilEnt, frame->first_ent, frame->last_ent, dst, next, prev);
        DllQueuePushNP(bin->first, bin->last, dst, next_in_bin, prev_in_bin);
      }
      P_Ent *old_next = dst->next;
      P_Ent *old_prev = dst->prev;
      P_Ent *old_next_in_bin = dst->next_in_bin;
      P_Ent *old_prev_in_bin = dst->prev_in_bin;
      {
        *dst = *src;
        dst->xf = NormXform(dst->xf);
      }
      dst->next = old_next;
      dst->prev = old_prev;
      dst->next_in_bin = old_next_in_bin;
      dst->prev_in_bin = old_prev_in_bin;
      dst->created_at_ns = frame->time_ns;
      dst->created_at_tick = frame->tick;
      ++frame->ents_count;
    }
  }
}

P_Constraint *P_PushConstraint(P_Frame *frame, P_ConstraintKey key)
{
  P_World *world = frame->world;
  P_Constraint *constraint = world->first_free_constraint;
  if (constraint)
  {
    SllStackPop(world->first_free_constraint);
  }
  else
  {
    constraint = PushStructNoZero(world->frames_arena, P_Constraint);
  }
  *constraint = P_NilConstraint;
  constraint->key = key;
  P_ConstraintBin *bin = &frame->constraint_bins[key.v % frame->constraint_bins_count];
  DllQueuePushNPZ(&P_NilConstraint, frame->first_constraint, frame->last_constraint, constraint, next, prev);
  DllQueuePushNP(bin->first, bin->last, constraint, next_in_bin, prev_in_bin);
  ++frame->constraints_count;
  return constraint;
}

P_Frame *P_FrameFromTick(P_World *world, i64 tick)
{
  P_Frame *result = &P_NilFrame;
  if (world->frame_bins_count > 0)
  {
    u64 hash = MixU64(tick);
    P_FrameBin *bin = &world->frame_bins[hash % world->frame_bins_count];
    for (P_Frame *frame = bin->first; frame; frame = frame->next_in_bin)
    {
      if (frame->tick == tick)
      {
        result = frame;
        break;
      }
    }
  }
  return result;
}

void P_ClearFrames(P_World *world, i64 tick_min, i64 tick_max)
{
  // TODO: Fast path for when range encompasses all frames in the world
  // TODO: Don't need linear search
  P_Frame *frame = world->first_frame;
  while (!P_IsFrameNil(frame))
  {
    P_Frame *next_frame = frame->next;
    if (frame->tick >= tick_min && frame->tick <= tick_max)
    {
      // Free ents
      if (!P_IsEntNil(frame->first_ent))
      {
        frame->last_ent->next = world->first_free_ent;
        world->first_free_ent = frame->first_ent;
      }

      // Free constraints
      if (!P_IsConstraintNil(frame->first_constraint))
      {
        frame->last_constraint->next = world->first_free_constraint;
        world->first_free_constraint = frame->first_constraint;
      }

      // Free frame
      u64 hash = MixU64(frame->tick);
      P_FrameBin *bin = &world->frame_bins[hash % world->frame_bins_count];
      DllQueueRemoveNPZ(&P_NilFrame, world->first_frame, world->last_frame, frame, next, prev);
      DllQueueRemoveNPZ(0, bin->first, bin->last, frame, next_in_bin, prev_in_bin);
      SllStackPush(world->first_free_frame, frame);
    }
    else
    {
      break;
    }
    frame = next_frame;
  }
}

P_Frame *P_PushFrame(P_World *world, P_Frame *src_frame, i64 tick)
{
  P_Frame *frame = world->first_free_frame;
  if (frame)
  {
    SllStackPop(world->first_free_frame);
    i64 old_ent_bins_count = frame->ent_bins_count;
    P_EntBin *old_ent_bins = frame->ent_bins;
    i64 old_constraint_bins_count = frame->constraint_bins_count;
    P_ConstraintBin *old_constraint_bins = frame->constraint_bins;
    {
      ZeroStruct(frame);
    }
    frame->ent_bins_count = old_ent_bins_count;
    frame->ent_bins = old_ent_bins;
    ZeroStructs(frame->ent_bins, frame->ent_bins_count);
    frame->constraint_bins_count = old_constraint_bins_count;
    frame->constraint_bins = old_constraint_bins;
    ZeroStructs(frame->constraint_bins, frame->constraint_bins_count);
  }
  else
  {
    frame = PushStruct(world->frames_arena, P_Frame);
  }

  {
    frame->world = world;
    frame->tick = tick;
    frame->time_ns = src_frame->time_ns;

    frame->first_ent = &P_NilEnt;
    frame->last_ent = &P_NilEnt;
    if (!frame->ent_bins)
    {
      frame->ent_bins_count = Kibi(16);
      frame->ent_bins = PushStructs(world->frames_arena, P_EntBin, frame->ent_bins_count);
    }

    frame->first_constraint = &P_NilConstraint;
    frame->last_constraint = &P_NilConstraint;
    if (!frame->constraint_bins)
    {
      frame->constraint_bins_count = Kibi(1);
      frame->constraint_bins = PushStructs(world->frames_arena, P_ConstraintBin, frame->constraint_bins_count);
    }
  }

  // Copy ents
  for (P_Ent *src = P_FirstEnt(src_frame); !P_IsEntNil(src); src = P_NextEnt(src))
  {
    P_Ent *dst = world->first_free_ent;
    if (dst)
    {
      SllStackPop(world->first_free_ent);
    }
    else
    {
      dst = PushStructNoZero(world->frames_arena, P_Ent);
    }
    *dst = *src;
    P_EntBin *bin = &frame->ent_bins[src->key.v % frame->ent_bins_count];
    DllQueuePushNPZ(&P_NilEnt, frame->first_ent, frame->last_ent, dst, next, prev);
    DllQueuePushNP(bin->first, bin->last, dst, next_in_bin, prev_in_bin);
    ++frame->ents_count;
  }

  // Copy constraints
  for (P_Constraint *src = P_FirstConstraint(src_frame); !P_IsConstraintNil(src); src = P_NextConstraint(src))
  {
    P_Constraint *dst = world->first_free_constraint;
    if (dst)
    {
      SllStackPop(world->first_free_constraint);
    }
    else
    {
      dst = PushStructNoZero(world->frames_arena, P_Constraint);
    }
    *dst = *src;
    P_ConstraintBin *bin = &frame->constraint_bins[src->key.v % frame->constraint_bins_count];
    DllQueuePushNPZ(&P_NilConstraint, frame->first_constraint, frame->last_constraint, dst, next, prev);
    DllQueuePushNP(bin->first, bin->last, dst, next_in_bin, prev_in_bin);
    ++frame->constraints_count;
  }

  // Clear frames
  P_ClearFrames(world, tick, I64Max);

  // Insert frame
  {
    u64 hash = MixU64(tick);
    P_FrameBin *bin = &world->frame_bins[hash % world->frame_bins_count];
    DllQueuePushNPZ(&P_NilFrame, world->first_frame, world->last_frame, frame, next, prev);
    DllQueuePushNPZ(0, bin->first, bin->last, frame, next_in_bin, prev_in_bin);
  }

  return frame;
}

////////////////////////////////////////////////////////////
//~ Step

void P_StepFrame(P_Frame *frame)
{
  TempArena scratch = BeginScratchNoConflict();
  P_World *world = frame->world;
  P_Frame *prev_frame = frame->prev;

  i64 sim_dt_ns = SIM_TICK_INTERVAL_NS;
  f64 sim_dt = SecondsFromNs(sim_dt_ns);

  //////////////////////////////
  //- Prune ents

  {
    i64 ents_to_prune_count = 0;
    P_EntKey *ents_to_prune = PushStructsNoZero(scratch.arena, P_EntKey, frame->ents_count);
    for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
    {
      if (ent->exists <= 0)
      {
        ents_to_prune[ents_to_prune_count++] = ent->key;
        if (!P_IsEntKeyNil(ent->weapon))
        {
          ents_to_prune[ents_to_prune_count++] = ent->weapon;
        }
      }
    }

    for (i64 prune_idx = 0; prune_idx < ents_to_prune_count; ++prune_idx)
    {
      // FIXME: Ensure sure prunes are received by clients
      P_EntKey key = ents_to_prune[prune_idx];
      P_Ent *ent = P_EntFromKey(frame, key);
      if (!P_IsEntNil(ent))
      {
        P_EntBin *bin = &frame->ent_bins[ent->key.v % frame->ent_bins_count];
        DllQueueRemoveNP(bin->first, bin->last, ent, next_in_bin, prev_in_bin);
        DllQueueRemoveNPZ(&P_NilEnt, frame->first_ent, frame->last_ent, ent, next, prev);
        frame->ents_count -= 1;
        SllStackPush(world->first_free_ent, ent);
      }
    }
  }

  //////////////////////////////
  //- Query ents

  b32 is_predicting = P_tl.is_predicting;
  P_Ent *local_player = P_EntFromKey(frame, P_tl.local_player);
  P_Ent *local_guy = P_EntFromKey(frame, local_player->guy);

  //////////////////////////////
  //- Spawn guys

  if (!is_predicting)
  {
    P_EntList queued_ents = Zi;
    for (P_Ent *player = P_FirstEnt(frame); !P_IsEntNil(player); player = P_NextEnt(player))
    {
      if (player->is_player)
      {
        if (P_IsEntKeyNil(player->guy))
        {
          player->guy = P_RandEntKey();
        }
        P_Ent *guy = P_EntFromKey(frame, player->guy);
        if (P_IsEntNil(guy))
        {
          guy = P_PushTempEnt(scratch.arena, &queued_ents);
          guy->is_guy = 1;
          guy->key = player->guy;
          guy->source = player->key;

          //- Choose guy spawn point
          {
            P_Ent *highest_scoring_spawn = &P_NilEnt;
            {
              Struct(SpawnNode)
              {
                SpawnNode *next;
                P_Ent *ent;
                f32 score;
              };

              i64 spawns_count = 0;
              SpawnNode *first_spawn = 0;
              SpawnNode *last_spawn = 0;

              // Push spawns
              for (P_Ent *spawn_ent = P_FirstEnt(frame); !P_IsEntNil(spawn_ent); spawn_ent = P_NextEnt(spawn_ent))
              {
                if (spawn_ent->is_guy_spawn)
                {
                  SpawnNode *spawn = PushStruct(scratch.arena, SpawnNode);
                  SllQueuePush(first_spawn, last_spawn, spawn);
                  spawn->ent = spawn_ent;
                  spawn->score = P_WorldPitch * 1000;
                  ++spawns_count;
                }
              }

              // Score spawns
              for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
              {
                b32 should_avoid = 0;
                if (ent->is_guy)
                {
                  should_avoid = 1;
                }
                if (P_MatchEntKey(ent->key, player->spawn))
                {
                  // Avoid old spawn
                  should_avoid = 1;
                }
                if (should_avoid)
                {
                  for (SpawnNode *spawn = first_spawn; spawn; spawn = spawn->next)
                  {
                    // TODO: Something better than linear distance for scoring
                    f32 score = Vec2Len(SubVec2(ent->xf.t, spawn->ent->xf.t));
                    spawn->score = MinF32(spawn->score, score);
                  }
                }
              }

              // Find highest scoring spawn
              i64 highest_score = -Inf;
              for (SpawnNode *spawn = first_spawn; spawn; spawn = spawn->next)
              {
                f32 rand_score_spread = 10;
                f32 virtual_score = spawn->score + rand_score_spread * Norm24(RandU64FromState(&world->rand));
                if (virtual_score > highest_score)
                {
                  highest_score = virtual_score;
                  highest_scoring_spawn = spawn->ent;
                }
              }
            }
            guy->xf = highest_scoring_spawn->xf;
            player->spawn = highest_scoring_spawn->key;
          }
        }
      }
    }
    P_SpawnEntsFromList(frame, queued_ents);
  }

  //////////////////////////////
  //- Equip spawned guys

  // TODO: Remove this (weapon testing)

  {
    P_EntList queued_ents = Zi;
    for (P_Ent *guy = P_FirstEnt(frame); !P_IsEntNil(guy); guy = P_NextEnt(guy))
    {
      if (guy->is_guy && guy->created_at_tick == frame->tick)
      {
        P_Ent *weapon = P_EntFromKey(frame, guy->weapon);
        if (!weapon->is_weapon)
        {
          weapon = P_PushTempEnt(scratch.arena, &queued_ents);
          weapon->is_weapon = 1;
          weapon->key = P_RandEntKey();
          weapon->source = guy->key;
          // weapon->is_uzi = 1;
          weapon->is_launcher = 1;
          guy->weapon = weapon->key;
        }
      }
    }
    P_SpawnEntsFromList(frame, queued_ents);
  }


  //////////////////////////////
  //- Update guy controls from player controls

  {
    for (P_Ent *guy = P_FirstEnt(frame); !P_IsEntNil(guy); guy = P_NextEnt(guy))
    {
      if (guy->is_guy)
      {
        ZeroStruct(&guy->control);
      }
    }
    for (P_Ent *player = P_FirstEnt(frame); !P_IsEntNil(player); player = P_NextEnt(player))
    {
      if (player->is_player)
      {
        P_Ent *guy = P_EntFromKey(frame, player->guy);
        if (!P_IsEntNil(guy))
        {
          guy->control = player->control;
        }
      }
    }

    // Normalize controls
    for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
    {
      ent->control.move = ClampVec2Len(ent->control.move, 0, 1);
    }
  }

  //////////////////////////////
  //- Integrate guy control forces

  for (P_Ent *guy = P_FirstEnt(frame); !P_IsEntNil(guy); guy = P_NextEnt(guy))
  {
    if (guy->is_guy && (!is_predicting || guy == local_guy))
    {
      P_Control control = guy->control;

      // Dampen movement
      {
        if (Vec2Len(guy->solved_v) > 0.001)
        {
          f32 damp_force = TweakFloat("Guy damp force", 50, 0, 100);
          Vec2 damp = MulVec2(NegVec2(guy->solved_v), damp_force * sim_dt);
          guy->solved_v = AddVec2(guy->solved_v, damp);
        }
        else
        {
          guy->solved_v = VEC2(0, 0);
        }
      }

      // Integrate linear movement
      {
        f32 move_force = TweakFloat("Guy move force", 400, 0, 400);
        f32 max_speed = TweakFloat("Guy max speed", 10, 0, 20);
        Vec2 new_velocity = guy->solved_v;
        new_velocity = AddVec2(new_velocity, MulVec2(control.move, move_force * sim_dt));
        if (Vec2Len(new_velocity) > max_speed)
        {
          new_velocity = Vec2WithLen(new_velocity, max_speed);
        }
        guy->solved_v = new_velocity;
      }

      // Integrate look
      {
        f32 turn_rate = TweakFloat("Guy turn rate", 1, 0, 1);
        f32 cur_angle = AngleFromVec2(guy->xf.r);
        f32 desired_angle = AngleFromVec2(control.look);
        f32 diff = UnwindAngleF32(desired_angle - cur_angle);
        f32 look_force = 1.0 / (sim_dt * sim_dt) * turn_rate;
        guy->solved_w = diff * sim_dt * look_force;
      }
    }
  }

  //////////////////////////////
  //- Setup constraints store

  i32 solver_steps_count = SIM_PHYSICS_SUBSTEPS;
  f32 solver_dt = sim_dt / solver_steps_count;

  // Solid params
  // SoftSpring solid_spring = MakeSpring(TweakFloat("Contact spring hz", 25, 5, 200), TweakFloat("Contact spring damp", 10, 5, 100), solver_dt);
  SoftSpring solid_spring = MakeSpring(TweakFloat("Contact spring hz", 100, 5, 200), TweakFloat("Contact spring damp", 10, 5, 100), solver_dt);
  f32 solid_pushout_velocity = TweakFloat("Contact spring pushout", 3, 0, 50);

  // Gentle params
  // f32 gentle_pushout_factor = TweakFloat("Gentle pushout factor", 10, 0, 50);
  f32 gentle_pushout_factor = TweakFloat("Gentle pushout factor", 0.5, 0, 50);

  //////////////////////////////
  //- Bake world

  {
    u64 desired_bake_hash = world->tiles_hash;
    if (desired_bake_hash != world->baked_hash)
    {
      LogDebugF("Bake step");
      ResetArena(world->bake_arena);
      world->walls_space = P_SpaceFromWalls(world->bake_arena, frame);
      world->baked_hash = desired_bake_hash;
    }
  }

  //////////////////////////////
  //- Build pre-solve space from ents

  P_Space pre_solve_ents_space = P_SpaceFromEnts(scratch.arena, frame);

  //////////////////////////////
  //- Generate guy constraints

  for (P_Ent *ent0 = P_FirstEnt(frame); !P_IsEntNil(ent0); ent0 = P_NextEnt(ent0))
  {
    if (ent0->is_guy)
    {
      P_Shape shape0 = P_WorldShapeFromEnt(ent0);
      Rng2 aabb0 = P_BoundingBoxFromShape(shape0);

      Rng2 query_rect = Zi;
      query_rect.p0 = FloorVec2(aabb0.p0);
      query_rect.p1 = CeilVec2(aabb0.p1);
      query_rect.p1.x = MaxF32(query_rect.p1.x, query_rect.p0.x + 1);
      query_rect.p1.y = MaxF32(query_rect.p1.y, query_rect.p0.y + 1);

      for (i32 query_y = query_rect.p0.y; query_y < query_rect.p1.y; ++query_y)
      {
        for (i32 query_x = query_rect.p0.x; query_x < query_rect.p1.x; ++query_x)
        {
          P_SpaceCell cells[] = {
            P_SpaceCellFromPos(&pre_solve_ents_space, VEC2(query_x, query_y)),
            P_SpaceCellFromPos(&world->walls_space, VEC2(query_x, query_y)),
          };
          for (i64 cell_idx = 0; cell_idx < countof(cells); ++cell_idx)
          {
            P_SpaceCell cell = cells[cell_idx];
            for (P_SpaceEntryNode *space_entry_node = cell.first; space_entry_node; space_entry_node = space_entry_node->next)
            {
              P_SpaceEntry *space_entry = &space_entry_node->entry;
              Rng2 aabb1 = P_BoundingBoxFromShape(space_entry->shape);
              P_Ent *ent1 = P_EntFromKey(frame, (P_EntKey) { .v = space_entry->shape_id });
              if (!P_MatchEntKey(ent0->key, ent1->key) && IsIntersectingRng2(aabb0, aabb1))
              {
                P_Shape shape1 = space_entry->shape;
                b32 is_static_collision = P_IsEntNil(ent1);
                b32 is_guy_on_guy_collision = ent0->is_guy && ent1->is_guy;

                if (is_static_collision || is_guy_on_guy_collision)
                {
                  P_ConstraintKey constraint_key = Zi;
                  {
                    // Deterministic shape ID order for consistent constraint lookup
                    u64 shape_id0 = ent0->key.v;
                    u64 shape_id1 = space_entry->shape_id;
                    if (shape_id0 > shape_id1)
                    {
                      u64 tmp = shape_id0;
                      shape_id0 = shape_id1;
                      shape_id1 = tmp;
                    }
                    constraint_key = P_ConstraintKeyFromU64s(shape_id0, shape_id1);
                  }
                  P_Constraint *constraint = P_ConstraintFromKey(frame, constraint_key);
                  if (constraint->last_touched_tick < frame->tick)
                  {
                    P_CollisionResult collision = P_CollisionResultFromShapes(shape0, shape1);

                    b32 skip_collision = 0;
                    skip_collision = skip_collision || collision.collision_points_count <= 0;
                    if (!skip_collision && !IsVec2Zero(space_entry->dir))
                    {
                      // Skip collision if normal violates one-way direction
                      // f32 threshold = 0.5;
                      f32 threshold = 0;
                      skip_collision = DotVec2(space_entry->dir, collision.collision_normal) >= threshold;
                    }

                    if (!skip_collision)
                    {
                      if (P_IsConstraintNil(constraint))
                      {
                        constraint = P_PushConstraint(frame, constraint_key);
                      }
                      constraint->last_touched_tick = frame->tick;
                      constraint->normal = collision.collision_normal;
                      // constraint->friction = SqrtF32(ent0->friction * ent1->friction);
                      constraint->friction = 0;

                      if (is_static_collision)
                      {
                        constraint->flags |= P_ConstraintFlag_Solid;
                      }
                      else if (is_guy_on_guy_collision)
                      {
                        constraint->flags |= P_ConstraintFlag_Gentle;
                        // constraint->flags |= P_ConstraintFlag_NoWarmStart;
                      }

                      // TODO: Real masses
                      f32 inv_m0 = 10;
                      f32 inv_m1 = 10;
                      f32 inv_i0 = 0;
                      f32 inv_i1 = 0;

                      // Treat statics / non-predicted ents as infinite-mass
                      if (!ent0->is_guy || (is_predicting && !P_MatchEntKey(ent0->key, local_guy->key)))
                      {
                        inv_m0 = 0;
                        inv_i0 = 0;
                      }
                      if (!ent1->is_guy || (is_predicting && !P_MatchEntKey(ent1->key, local_guy->key)))
                      {
                        inv_m1 = 0;
                        inv_i1 = 0;
                      }

                      constraint->ent0 = ent0->key;
                      constraint->ent1 = ent1->key;
                      constraint->static_center0 = shape0.center_of_mass;
                      constraint->static_center1 = shape1.center_of_mass;

                      constraint->inv_m0 = inv_m0;
                      constraint->inv_m1 = inv_m1;
                      constraint->inv_i0 = inv_i0;
                      constraint->inv_i1 = inv_i1;

                      // Delete old contacts that are no longer present
                      for (i32 contact_point_idx = 0; contact_point_idx < constraint->points_count; ++contact_point_idx)
                      {
                        P_ContactPoint *contact = &constraint->points[contact_point_idx];
                        u32 id = contact->id;
                        b32 match = 0;
                        for (i32 collision_point_idx = 0; collision_point_idx < collision.collision_points_count; ++collision_point_idx)
                        {
                          if (collision.collision_points[collision_point_idx].id == id)
                          {
                            match = 1;
                            break;
                          }
                        }
                        if (!match)
                        {
                          // Delete contact by replacing with last in array
                          *contact = constraint->points[constraint->points_count - 1];
                          constraint->points_count -= 1;
                          contact_point_idx -= 1;
                        }
                      }

                      // Create / update contacts from collision
                      for (i32 collision_point_idx = 0; collision_point_idx < collision.collision_points_count; ++collision_point_idx)
                      {
                        P_CollisionPoint collision_point = collision.collision_points[collision_point_idx];

                        u32 id = collision_point.id;
                        P_ContactPoint *contact = 0;
                        {
                          for (i32 contact_point_idx = 0; contact_point_idx < constraint->points_count; ++contact_point_idx)
                          {
                            P_ContactPoint *tmp = &constraint->points[contact_point_idx];
                            if (tmp->id == id)
                            {
                              contact = tmp;
                              break;
                            }
                          }
                          if (!contact)
                          {
                            contact = &constraint->points[constraint->points_count];
                            constraint->points_count += 1;
                            ZeroStruct(contact);
                          }
                        }
                        contact->id = id;

                        Vec2 vcp0 = SubVec2(collision_point.p, shape0.center_of_mass);
                        Vec2 vcp1 = SubVec2(collision_point.p, shape1.center_of_mass);

                        contact->vcp0 = vcp0;
                        contact->vcp1 = vcp1;
                        contact->starting_separation = collision_point.separation;
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }

  //////////////////////////////
  //- Prune constraints

  {
    i64 prune_constraints_count = 0;
    P_Constraint **prune_constraints = PushStructsNoZero(scratch.arena, P_Constraint *, frame->constraints_count);
    for (P_Constraint *constraint = P_FirstConstraint(frame); !P_IsConstraintNil(constraint); constraint = P_NextConstraint(constraint))
    {
      b32 prune = 1;
      if (constraint->last_touched_tick == frame->tick)
      {
        prune = 0;
      }
      if (prune)
      {
        prune_constraints[prune_constraints_count] = constraint;
        prune_constraints_count += 1;
      }
    }

    for (i64 prune_idx = 0; prune_idx < prune_constraints_count; ++prune_idx)
    {
      P_Constraint *constraint = prune_constraints[prune_idx];
      P_ConstraintBin *bin = &frame->constraint_bins[constraint->key.v % frame->constraint_bins_count];
      DllQueueRemoveNP(bin->first, bin->last, constraint, next_in_bin, prev_in_bin);
      DllQueueRemoveNPZ(&P_NilConstraint, frame->first_constraint, frame->last_constraint, constraint, next, prev);
      frame->constraints_count -= 1;
      SllStackPush(world->first_free_constraint, constraint);
    }
  }

  //////////////////////////////
  //- Run solver steps

  for (i32 solver_step_idx = 0; solver_step_idx < solver_steps_count; ++solver_step_idx)
  {
    //////////////////////////////
    //- Prepare constraints

    for (P_Constraint *constraint = P_FirstConstraint(frame); !P_IsConstraintNil(constraint); constraint = P_NextConstraint(constraint))
    {
      Vec2 normal = constraint->normal;
      Vec2 tangent = PerpVec2(normal);
      f32 inv_m0 = constraint->inv_m0;
      f32 inv_m1 = constraint->inv_m1;
      f32 inv_i0 = constraint->inv_i0;
      f32 inv_i1 = constraint->inv_i1;

      for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
      {
        P_ContactPoint *contact = &constraint->points[contact_idx];
        Vec2 vcp0 = contact->vcp0;
        Vec2 vcp1 = contact->vcp1;

        // Compute normal mass
        {
          f32 vcp0_wedge = WedgeVec2(vcp0, normal);
          f32 vcp1_wedge = WedgeVec2(vcp1, normal);
          f32 k = (inv_m0 + inv_m1) + (inv_i0 * vcp0_wedge * vcp0_wedge) + (inv_i1 * vcp1_wedge * vcp1_wedge);
          contact->inv_normal_mass = k > 0.0f ? 1.0f / k : 0.0f;
        }

        // Compute tangent mass
        {
          f32 vcp0_wedge = WedgeVec2(vcp0, tangent);
          f32 vcp1_wedge = WedgeVec2(vcp1, tangent);
          f32 k = (inv_m0 + inv_m1) + (inv_i0 * vcp0_wedge * vcp0_wedge) + (inv_i1 * vcp1_wedge * vcp1_wedge);
          contact->inv_tangent_mass = k > 0.0f ? 1.0f / k : 0.0f;
        }
      }
    }

    //////////////////////////////
    //- Warm start constraints

    for (P_Constraint *constraint = P_FirstConstraint(frame); !P_IsConstraintNil(constraint); constraint = P_NextConstraint(constraint))
    {
      if (!(constraint->flags & P_ConstraintFlag_NoWarmStart))
      {
        P_Ent *ent0 = P_EntFromKey(frame, constraint->ent0);
        P_Ent *ent1 = P_EntFromKey(frame, constraint->ent1);

        Vec2 v0 = ent0->solved_v;
        Vec2 v1 = ent1->solved_v;
        f32 w0 = ent0->solved_w;
        f32 w1 = ent1->solved_w;

        Vec2 normal = constraint->normal;
        Vec2 tangent = PerpVec2(normal);

        for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
        {
          P_ContactPoint *contact = &constraint->points[contact_idx];
          Vec2 vcp0 = contact->vcp0;
          Vec2 vcp1 = contact->vcp1;

          Vec2 impulse = AddVec2(MulVec2(normal, contact->solved_normal_impulse), MulVec2(tangent, contact->solved_tangent_impulse));
          // impulse = MulVec2(impulse, inv_num_points);

          v0 = SubVec2(v0, MulVec2(impulse, constraint->inv_m0));
          v1 = AddVec2(v1, MulVec2(impulse, constraint->inv_m1));
          w0 -= WedgeVec2(vcp0, impulse) * constraint->inv_i0;
          w1 += WedgeVec2(vcp1, impulse) * constraint->inv_i1;
        }

        if (!P_IsEntNil(ent0))
        {
          ent0->solved_v = v0;
          ent0->solved_w = w0;
        }
        if (!P_IsEntNil(ent1))
        {
          ent1->solved_v = v1;
          ent1->solved_w = w1;
        }
      }
    }

    //////////////////////////////
    //- Solve constraints

    // TODO: Solve wall constraints last

    for (P_Constraint *constraint = P_FirstConstraint(frame); !P_IsConstraintNil(constraint); constraint = P_NextConstraint(constraint))
    {
      P_Ent *ent0 = P_EntFromKey(frame, constraint->ent0);
      P_Ent *ent1 = P_EntFromKey(frame, constraint->ent1);

      Vec2 normal = constraint->normal;
      Vec2 tangent = PerpVec2(normal);

      f32 inv_m0 = constraint->inv_m0;
      f32 inv_m1 = constraint->inv_m1;
      f32 inv_i0 = constraint->inv_i0;
      f32 inv_i1 = constraint->inv_i1;
      Vec2 v0 = ent0->solved_v;
      Vec2 v1 = ent1->solved_v;
      f32 w0 = ent0->solved_w;
      f32 w1 = ent1->solved_w;

      Vec2 center0 = constraint->static_center0;
      Vec2 center1 = constraint->static_center1;
      if (!P_IsEntNil(ent0))
      {
        center0 = P_WorldShapeFromEnt(ent0).center_of_mass;
      }
      if (!P_IsEntNil(ent1))
      {
        center1 = P_WorldShapeFromEnt(ent1).center_of_mass;
      }

      //- Solve solid constraint
      if (constraint->flags & P_ConstraintFlag_Solid)
      {
        // Normal impulse
        for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
        {
          P_ContactPoint *contact = &constraint->points[contact_idx];
          Vec2 vcp0 = contact->vcp0;
          Vec2 vcp1 = contact->vcp1;
          Vec2 p0 = AddVec2(center0, vcp0);
          Vec2 p1 = AddVec2(center1, vcp1);
          f32 separation = DotVec2(SubVec2(p1, p0), normal) + contact->starting_separation;

          f32 velocity_bias = 0.0;
          f32 mass_scale = 1.0;
          f32 impulse_scale = 0.0;

          // TODO: Do a relaxation pass without bias
          b32 apply_bias = 1;
          if (separation > 0.0)
          {
            // Speculative
            velocity_bias = separation / solver_dt;
          }
          else if (apply_bias)
          {
            // Soft constraint
            SoftSpring softness = solid_spring;
            f32 pushout_velocity = solid_pushout_velocity;
            mass_scale = softness.mass_scale;
            impulse_scale = softness.impulse_scale;
            velocity_bias = MaxF32(softness.bias_rate * separation, -pushout_velocity);
          }

          Vec2 vel0 = AddVec2(v0, MulPerpVec2(vcp0, w0));
          Vec2 vel1 = AddVec2(v1, MulPerpVec2(vcp1, w1));
          Vec2 vrel = SubVec2(vel0, vel1);

          f32 k = contact->inv_normal_mass;

          // To be applied along normal
          f32 vn = DotVec2(vrel, normal);
          f32 j = ((k * mass_scale) * (vn - velocity_bias)) - (contact->solved_normal_impulse * impulse_scale);

          f32 old_impulse = contact->solved_normal_impulse;
          f32 new_impulse = MaxF32(old_impulse + j, 0);
          f32 delta = new_impulse - old_impulse;
          contact->solved_normal_impulse = new_impulse;

          Vec2 impulse = MulVec2(normal, delta);
          v0 = SubVec2(v0, MulVec2(impulse, inv_m0));
          v1 = AddVec2(v1, MulVec2(impulse, inv_m1));
          w0 -= WedgeVec2(vcp0, impulse) * inv_i0;
          w1 += WedgeVec2(vcp1, impulse) * inv_i1;
        }

        // Tangent impulse
        for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
        {
          P_ContactPoint *contact = &constraint->points[contact_idx];
          Vec2 vcp0 = contact->vcp0;
          Vec2 vcp1 = contact->vcp1;

          Vec2 vel0 = AddVec2(v0, MulPerpVec2(vcp0, w0));
          Vec2 vel1 = AddVec2(v1, MulPerpVec2(vcp1, w1));
          Vec2 vrel = SubVec2(vel0, vel1);

          f32 k = contact->inv_tangent_mass;

          // To be applied along tangent
          f32 vt = DotVec2(vrel, tangent);
          f32 j = vt * k;

          f32 max_friction = constraint->friction * contact->solved_normal_impulse;
          f32 old_impulse = contact->solved_tangent_impulse;
          f32 new_impulse = ClampF32(old_impulse + j, -max_friction, max_friction);
          f32 delta = new_impulse - old_impulse;
          contact->solved_tangent_impulse = new_impulse;

          Vec2 impulse = MulVec2(tangent, delta);
          v0 = SubVec2(v0, MulVec2(impulse, inv_m0));
          v1 = AddVec2(v1, MulVec2(impulse, inv_m1));
          w0 -= WedgeVec2(vcp0, impulse) * inv_i0;
          w1 += WedgeVec2(vcp1, impulse) * inv_i1;
        }

        if (!P_IsEntNil(ent0))
        {
          ent0->solved_v = v0;
          ent0->solved_w = w0;
        }
        if (!P_IsEntNil(ent1))
        {
          ent1->solved_v = v1;
          ent1->solved_w = w1;
        }
      }

      //- Solve gentle constraint
      if (constraint->flags & P_ConstraintFlag_Gentle)
      {
        // Normal impulse
        for (i32 contact_idx = 0; contact_idx < constraint->points_count; ++contact_idx)
        {
          P_ContactPoint *contact = &constraint->points[contact_idx];
          Vec2 vcp0 = contact->vcp0;
          Vec2 vcp1 = contact->vcp1;
          Vec2 p0 = AddVec2(center0, vcp0);
          Vec2 p1 = AddVec2(center1, vcp1);
          f32 separation = DotVec2(SubVec2(p1, p0), normal) + contact->starting_separation;

          f32 j = -separation * solver_dt * gentle_pushout_factor;

          f32 old_impulse = contact->solved_normal_impulse;
          f32 new_impulse = MaxF32(old_impulse + j, 0);
          f32 delta = new_impulse - old_impulse;
          contact->solved_normal_impulse = new_impulse;

          Vec2 impulse = MulVec2(normal, delta);
          v0 = SubVec2(v0, MulVec2(impulse, inv_m0));
          v1 = AddVec2(v1, MulVec2(impulse, inv_m1));
          w0 -= WedgeVec2(vcp0, impulse) * inv_i0;
          w1 += WedgeVec2(vcp1, impulse) * inv_i1;
        }

        if (!P_IsEntNil(ent0))
        {
          ent0->solved_v = v0;
          ent0->solved_w = w0;
        }
        if (!P_IsEntNil(ent1))
        {
          ent1->solved_v = v1;
          ent1->solved_w = w1;
        }
      }
    }

    //////////////////////////////
    //- Integrate velocities

    for (P_Ent *ent = P_FirstEnt(frame); !P_IsEntNil(ent); ent = P_NextEnt(ent))
    {
      if (!is_predicting || ent == local_guy)
      {
        Xform xf = ent->xf;
        xf.t = AddVec2(xf.t, MulVec2(ent->solved_v, solver_dt));
        xf.r = RotateVec2Angle(xf.r, ent->solved_w * solver_dt);
        ent->xf = xf;
      }
    }
  }

  //////////////////////////////
  //- Build post-solve space from ents

  P_Space post_solve_ents_space = P_SpaceFromEnts(scratch.arena, frame);

  //////////////////////////////
  //- Move bullets

  for (P_Ent *bullet = P_FirstEnt(frame); !P_IsEntNil(bullet); bullet = P_NextEnt(bullet))
  {
    if (bullet->is_bullet)
    {
      Vec2 start = bullet->bullet_start;
      Vec2 end = bullet->bullet_end;
      Vec2 vel = SubVec2(end, start);
      bullet->bullet_start = end;
      bullet->bullet_end = AddVec2(end, vel);
    }
  }

  //////////////////////////////
  //- Fire bullets

  // TODO: Remove this

  {
    P_EntList bullets_to_spawn = Zi;
    for (P_Ent *firer = P_FirstEnt(frame); !P_IsEntNil(firer); firer = P_NextEnt(firer))
    {
      P_Ent *weapon = P_EntFromKey(frame, firer->weapon);
      if (weapon->is_weapon && firer->control.fire_held)
      // if (weapon->is_weapon && firer->control.fire_presses)
      {
        // i64 fire_delta_ns = frame->time_ns - firer->last_fire_ns;

        // i64 single_bullet_delta_ns = NsFromSeconds(1) / firer->fire_rate;

        // i64 tick_bullets_count = sim_dt * firer->fire_rate;

        f32 fire_rate = 50;
        f32 bullets_per_fire = 1;
        f32 spread = Tau * 0.05;
        // f32 spread = Tau * 0.01;
        f32 tweak_speed = TweakFloat("Bullet speed", 100, 1, 100);
        // f32 tweak_speed = TweakFloat("Bullet speed", 1, 1, 100);

        b32 can_fire = (firer->last_fire_ns + NsFromSeconds(1.0 / fire_rate)) <= frame->time_ns;

        Vec2 fire_pos = Zi;
        Vec2 fire_dir = Zi;
        Vec2 fire_base0 = Zi;
        Vec2 fire_base1 = Zi;
        if (can_fire)
        {
          Vec2 look = firer->control.look;
          P_Anim anim = P_AnimFromEnt(frame, firer);
          SPR_Sprite body = SPR_SpriteFromSheet(anim.sheet, anim.span, anim.frame_seq);
          SPR_Sprite wep = SPR_SpriteFromSheet(anim.wep_sheet, anim.span, anim.frame_seq);

          //- Compute sprite transforms
          Affine ent_to_world_af = MulAffineXform(AffineIdentity, firer->xf);
          Affine body_pix_to_world_af = AffineIdentity;
          Affine wep_pix_to_world_af = AffineIdentity;
          {
            Vec2 pix_scale = VEC2(1.0 / P_CellsPerMeter, 1.0 / P_CellsPerMeter);

            //- Compute body transform
            Affine body_pix_to_ent_af = AffineIdentity;
            {
              body_pix_to_ent_af = ScaleAffine(body_pix_to_ent_af, pix_scale);

              SPR_Ray anchor_ray = body.rays[SPR_RayKind_Anchor];
              body_pix_to_ent_af = RotateAffine(body_pix_to_ent_af, InvertRot(anchor_ray.dir));
              body_pix_to_ent_af = TranslateAffine(body_pix_to_ent_af, NegVec2(anchor_ray.pos));
            }

            //- Compute weapon transform
            Affine wep_pix_to_ent_af = AffineIdentity;
            {
              wep_pix_to_ent_af = ScaleAffine(wep_pix_to_ent_af, pix_scale);

              SPR_Ray body_anchor_ray = body.rays[SPR_RayKind_Anchor];
              SPR_Ray body_ap_ray = body.rays[SPR_RayKind_Ap];
              wep_pix_to_ent_af = RotateAffine(wep_pix_to_ent_af, InvertRot(body_anchor_ray.dir));
              wep_pix_to_ent_af = TranslateAffine(wep_pix_to_ent_af, SubVec2(body_ap_ray.pos, body_anchor_ray.pos));
              wep_pix_to_ent_af = RotateAffine(wep_pix_to_ent_af, NegVec2(body_ap_ray.dir));

              SPR_Ray anchor_ray = wep.rays[SPR_RayKind_Anchor];
              wep_pix_to_ent_af = RotateAffine(wep_pix_to_ent_af, anchor_ray.dir);
              wep_pix_to_ent_af = TranslateAffine(wep_pix_to_ent_af, NegVec2(anchor_ray.pos));
            }

            body_pix_to_world_af = MulAffine(ent_to_world_af, body_pix_to_ent_af);
            wep_pix_to_world_af = MulAffine(ent_to_world_af, wep_pix_to_ent_af);
          }

          SPR_Ray fire_ray = wep.rays[SPR_RayKind_Ap];
          fire_pos = MulAffineVec2(wep_pix_to_world_af, fire_ray.pos);
          fire_dir = NormRot(MulAffineBasisVec2(wep_pix_to_world_af, fire_ray.dir));

          fire_base0 = MulVec2(PerpVec2(NegVec2(firer->xf.r)), WedgeVec2(firer->xf.r, SubVec2(firer->xf.t, fire_pos)));
          fire_base0 = AddVec2(fire_base0, firer->xf.t);

          Vec2 chamber_pos = MulAffineVec2(body_pix_to_world_af, body.rays[SPR_RayKind_Ap].pos);

          fire_base1 = MulVec2(PerpVec2(fire_dir), WedgeVec2(fire_dir, SubVec2(fire_pos, chamber_pos)));
          fire_base1 = AddVec2(fire_base1, chamber_pos);

          P_DebugDrawLine(fire_base0, fire_base1, Color_Yellow);
          P_DebugDrawLine(fire_base1, fire_pos, Color_Green);
          P_DebugDrawPoint(fire_base0, Color_Yellow);
          P_DebugDrawPoint(fire_base1, Color_Green);
          P_DebugDrawPoint(fire_pos, Color_Red);
        }

        // FIXME: Prevent obstructed weapons from firing through walls

        if (can_fire)
        {
          i64 tick_bullets_count = bullets_per_fire;
          if (tick_bullets_count > 0)
          {
            P_Shape firer_world_shape = P_WorldShapeFromEnt(firer);

            // Vec2 fire_pos = P_EdgePointFromShape(firer_world_shape, firer->control.look);
            // Vec2 fire_dir = firer->control.look;

            for (i64 bullet_idx = 0; bullet_idx < tick_bullets_count; ++bullet_idx)
            {
              P_Ent *bullet = P_PushTempEnt(scratch.arena, &bullets_to_spawn);
              bullet->is_bullet = 1;
              bullet->key = P_RandEntKey();

              f32 rand_speed = Norm24(P_RandU64FromEnt(firer)) - 0.5;
              f32 rand_angle = Norm24(P_RandU64FromEnt(firer)) - 0.5;

              f32 speed = tweak_speed * sim_dt;
              f32 angle = AngleFromVec2(fire_dir);

              speed += (speed * 0.5) * rand_speed;
              angle += rand_angle * spread;

              Vec2 dir = Vec2FromAngle(angle);

              bullet->bullet_base0 = fire_base0;
              bullet->bullet_base1 = fire_base1;
              bullet->bullet_start = fire_pos;
              bullet->bullet_end = AddVec2(bullet->bullet_start, MulVec2(dir, speed));
              bullet->source = weapon->key;
              bullet->damage_attribution = firer->source;
            }
          }
          firer->last_fire_ns = frame->time_ns;
        }
      }
    }
    P_SpawnEntsFromList(frame, bullets_to_spawn);
  }

  //////////////////////////////
  //- Update bullet hits

  // TODO: Separate 'hits' from bullets, so that bullets can have multiple hits

  for (P_Ent *bullet = P_FirstEnt(frame); !P_IsEntNil(bullet); bullet = P_NextEnt(bullet))
  {
    if (bullet->is_bullet)
    {
      P_Ent *bullet_weapon = P_EntFromKey(frame, bullet->source);
      P_Ent *bullet_guy = P_EntFromKey(frame, bullet_weapon->source);
      P_Ent *bullet_damager = P_EntFromKey(frame, bullet->damage_attribution);

      bullet->has_hit = 0;

      Struct(BulletPath)
      {
        BulletPath *next;
        Vec2 start;
        Vec2 end;
      };
      BulletPath *first_bullet_path = 0;
      BulletPath *last_bullet_path = 0;

      if (bullet->created_at_tick == frame->tick)
      {
        // On bullet's first tick, we want to ensure that the firer/weapon
        // wasn't obstructed (e.g. to prevent shooting through walls), so we
        // insert a path from the bullet's base to its starting position before
        // its actual firing path
        {
          // Firer origin -> weapon chamber path
          BulletPath *path = PushStruct(scratch.arena, BulletPath);
          SllQueuePush(first_bullet_path, last_bullet_path, path);
          path->start = bullet->bullet_base0;
          path->end = bullet->bullet_base1;
        }
        {
          // Weapon chamber -> bullet start path
          BulletPath *path = PushStruct(scratch.arena, BulletPath);
          SllQueuePush(first_bullet_path, last_bullet_path, path);
          path->start = bullet->bullet_base1;
          path->end = bullet->bullet_start;
        }
      }

      {
        BulletPath *path = PushStruct(scratch.arena, BulletPath);
        SllQueuePush(first_bullet_path, last_bullet_path, path);
        path->start = bullet->bullet_start;
        path->end = bullet->bullet_end;
      }

      P_EntKey victim_key = Zi;
      P_RaycastResult victim_raycast = Zi;
      b32 hit = 0;
      {
        for (BulletPath *path = first_bullet_path; path && !hit; path = path->next)
        {
          Vec2 path_dir = SubVec2(path->end, path->start);
          P_Space *cast_spaces[] = {
            &world->walls_space,
            &post_solve_ents_space,
          };
          P_SpaceEntryList cast_entries = Zi;
          P_UniqueSpaceEntriesFromRay(
            scratch.arena,
            &cast_entries,
            countof(cast_spaces),
            cast_spaces,
            path->start,
            path->end
          );
          f32 closest_len_sq = Inf;
          for (P_SpaceEntryNode *entry_node = cast_entries.first; entry_node; entry_node = entry_node->next)
          {
            P_SpaceEntry *entry = &entry_node->entry;
            P_EntKey potential_victim_key = (P_EntKey) { .v = entry->shape_id };
            if (!P_MatchEntKey(potential_victim_key, bullet_guy->key) || P_IsEntKeyNil(bullet_guy->key))
            {
              P_Shape potential_victim_shape = entry->shape;
              P_RaycastResult entrance_raycast = P_RaycastShape(potential_victim_shape, path->start, path_dir);
              Vec2 entrance = entrance_raycast.p;
              if (entrance_raycast.is_intersecting)
              {
                P_RaycastResult exit_raycast = P_RaycastShape(potential_victim_shape, path->start, NegVec2(path_dir));
                Vec2 exit = exit_raycast.p;
                f32 da = DotVec2(path_dir, SubVec2(entrance, path->start));
                f32 db = DotVec2(path_dir, SubVec2(exit, path->start));
                if (db > 0 && (da <= Vec2LenSq(path_dir) || da <= 0))
                {
                  f32 len_sq = Vec2LenSq(SubVec2(entrance_raycast.p, path->start));
                  if (len_sq < closest_len_sq)
                  {
                    closest_len_sq = len_sq;
                    victim_key = potential_victim_key;
                    victim_raycast = entrance_raycast;
                    hit = 1;
                  }
                }
              }
            }
          }
        }
      }
      P_Ent *victim = P_EntFromKey(frame, victim_key);

      // TODO: Truncate bullet trail
      if (hit)
      {
        bullet->has_hit = 1;
        bullet->hit_entry = victim_raycast.p;
        bullet->hit_entry_normal = victim_raycast.normal;
        // bullet->bullet_end = bullet->hit_entry;
        bullet->exists = 0;
        if (victim->is_guy)
        {
          bullet->hit_material = P_MaterialKind_Flesh;
        }
        else
        {
          bullet->hit_material = P_MaterialKind_Wall;
        }
      }

      // TODO: Remove this
      if (!P_IsEntNil(victim))
      {
        if (bullet_damager->is_player)
        {
          victim->damage_attribution = bullet_damager->key;
        }
        victim->health -= 0.25;
      }

      // Prune out of bounds bullet
      Rng2 bounds = Zi;
      bounds.p0 = VEC2(-P_WorldPitch / 2, -P_WorldPitch / 2);
      bounds.p1 = VEC2(P_WorldPitch / 2, P_WorldPitch / 2);
      if (
        bullet->bullet_start.x < bounds.p0.x || bullet->bullet_start.y < bounds.p0.y ||
        bullet->bullet_start.x > bounds.p1.x || bullet->bullet_start.y > bounds.p1.y
      )
      {
        bullet->exists = 0;
      }
    }
  }

  //////////////////////////////
  //- Kill guys

  for (P_Ent *guy = P_FirstEnt(frame); !P_IsEntNil(guy); guy = P_NextEnt(guy))
  {
    if (guy->is_guy)
    {
      if (guy->health <= 0)
      {
        P_Ent *old_guy = P_EntFromKey(prev_frame, guy->key);
        if (old_guy->health > 0)
        {
          P_Ent *player = P_EntFromKey(frame, guy->source);
          P_Ent *killer = P_EntFromKey(frame, guy->damage_attribution);
          if (player->is_player)
          {
            player->deaths += 1;
          }
          if (killer->is_player && !P_MatchEntKey(player->key, killer->key))
          {
            killer->kills += 1;
          }
          guy->exists = 0;
        }
      }
    }
  }

  //////////////////////////////
  //- Debug draw

  P_DebugDrawFrame(frame);

  //////////////////////////////
  //- End frame

  frame->time_ns += sim_dt_ns;

  EndScratch(scratch);
}