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 //------------------------------- -*- C++ -*- -------------------------------//
 // Copyright Celeritas contributors: see top-level COPYRIGHT file for details
 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
 //---------------------------------------------------------------------------//
 //! \file geocel/vg/VecgeomTrackView.hh
 //---------------------------------------------------------------------------//
 #pragma once
 
 #include <VecGeom/base/Config.h>
 #include <VecGeom/base/Cuda.h>
 #include <VecGeom/base/Version.h>
 #include <VecGeom/navigation/NavStateFwd.h>
 #include <VecGeom/navigation/NavigationState.h>
 #include <VecGeom/volumes/LogicalVolume.h>
 #include <VecGeom/volumes/PlacedVolume.h>
 
 #include "corecel/Config.hh"
 
 #include "corecel/Macros.hh"
 #include "corecel/math/Algorithms.hh"
 #include "corecel/math/ArrayUtils.hh"
 #include "corecel/math/SoftEqual.hh"
 #include "corecel/sys/ThreadId.hh"
 #include "geocel/Types.hh"
 
 #include "VecgeomData.hh"
 
 #include "detail/VecgeomCompatibility.hh"
 
 #ifdef VECGEOM_USE_SURF
 #    include "detail/SurfNavigator.hh"
 #elif VECGEOM_VERSION >= 0x020000
 #    include <VecGeom/navigation/BVHNavigator.h>
 #else
 #    include "detail/BVHNavigator.hh"
 #endif
 
 namespace celeritas
 {
 //---------------------------------------------------------------------------//
 /*!
  * Navigate through a VecGeom geometry on a single thread.
  *
  * For a description of ordering requirements, see:
  * \sa OrangeTrackView
  *
  * \code
     VecgeomTrackView geom(vg_params_ref, vg_state_ref, trackslot_id);
    \endcode
  *
  * The "next distance" is cached as part of `find_next_step`, but it is only
  * used when the immediate next call is `move_to_boundary`.
  */
 class VecgeomTrackView
 {
   public:
     //!@{
     //! \name Type aliases
     using Initializer_t = GeoTrackInitializer;
     using ParamsRef = NativeCRef<VecgeomParamsData>;
     using StateRef = NativeRef<VecgeomStateData>;
 #ifdef VECGEOM_USE_SURF
     using Navigator = celeritas::detail::SurfNavigator;
 #elif VECGEOM_VERSION >= 0x020000
     using Navigator = vecgeom::BVHNavigator;
 #else
     using Navigator = celeritas::detail::BVHNavigator;
 #endif
     //!@}
 
     //! Helper struct for initializing from an existing geometry state
     struct DetailedInitializer
     {
         VecgeomTrackView const& other;  //!< Existing geometry
         Real3 const& dir;  //!< New direction
     };
 
   public:
     // Construct from persistent and state data
     inline CELER_FUNCTION VecgeomTrackView(ParamsRef const& data,
                                            StateRef const& stateview,
                                            TrackSlotId tid);
 
     // Initialize the state
     inline CELER_FUNCTION VecgeomTrackView&
     operator=(Initializer_t const& init);
     // Initialize the state from a parent state and new direction
     inline CELER_FUNCTION VecgeomTrackView&
     operator=(DetailedInitializer const& init);
 
     //// STATIC ACCESSORS ////
 
     //! A tiny push to make sure tracks do not get stuck at boundaries
     static CELER_CONSTEXPR_FUNCTION real_type extra_push() { return 1e-13; }
 
     //// ACCESSORS ////
 
     //!@{
     //! State accessors
     CELER_FORCEINLINE_FUNCTION Real3 const& pos() const { return pos_; }
     CELER_FORCEINLINE_FUNCTION Real3 const& dir() const { return dir_; }
     //!@}
 
     // Get the current volume's ID
     inline CELER_FUNCTION VolumeId volume_id() const;
     // Get the ID of the current volume instance
     inline CELER_FUNCTION VolumeInstanceId volume_instance_id() const;
     // Get the depth in the geometry hierarchy
     inline CELER_FUNCTION LevelId level() const;
     // Get the volume instance ID for all levels
     inline CELER_FUNCTION void
     volume_instance_id(Span<VolumeInstanceId> levels) const;
 
     //!@{
     //! VecGeom states are never "on" a surface
     CELER_FUNCTION SurfaceId surface_id() const { return {}; }
     //!@}
 
     // Whether the track is outside the valid geometry region
     CELER_FORCEINLINE_FUNCTION bool is_outside() const;
     // Whether the track is exactly on a surface
     CELER_FORCEINLINE_FUNCTION bool is_on_boundary() const;
     //! Whether the last operation resulted in an error
     CELER_FORCEINLINE_FUNCTION bool failed() const { return false; }
 
     //// OPERATIONS ////
 
     // Find the distance to the next boundary (infinite max)
     inline CELER_FUNCTION Propagation find_next_step();
 
     // Find the distance to the next boundary, up to and including a step
     inline CELER_FUNCTION Propagation find_next_step(real_type max_step);
 
     // Find the safety at the current position (infinite max)
     inline CELER_FUNCTION real_type find_safety();
 
     // Find the safety at the current position up to a maximum step distance
     inline CELER_FUNCTION real_type find_safety(real_type max_step);
 
     // Move to the boundary in preparation for crossing it
     inline CELER_FUNCTION void move_to_boundary();
 
     // Move within the volume
     inline CELER_FUNCTION void move_internal(real_type step);
 
     // Move within the volume to a specific point
     inline CELER_FUNCTION void move_internal(Real3 const& pos);
 
     // Cross from one side of the current surface to the other
     inline CELER_FUNCTION void cross_boundary();
 
     // Change direction
     inline CELER_FUNCTION void set_dir(Real3 const& newdir);
 
   private:
     //// TYPES ////
 
     using Volume = vecgeom::LogicalVolume;
     using NavState = vecgeom::NavigationState;
 
     //// DATA ////
 
     //! Shared/persistent geometry data
     ParamsRef const& params_;
 
     //!@{
     //! Referenced thread-local data
     NavState& vgstate_;
     NavState& vgnext_;
     Real3& pos_;
     Real3& dir_;
 #ifdef VECGEOM_USE_SURF
     long& next_surface_;
 #endif
     //!@}
 
     // Temporary data
     real_type next_step_{0};
 
     //// HELPER FUNCTIONS ////
 
     // Whether any next distance-to-boundary has been found
     inline CELER_FUNCTION bool has_next_step() const;
 
     // Whether the next distance-to-boundary is to a surface
     inline CELER_FUNCTION bool is_next_boundary() const;
 
     //! Get a reference to the current volume
     inline CELER_FUNCTION Volume const& volume() const;
 
 #ifdef VECGEOM_USE_SURF
     static CELER_CONSTEXPR_FUNCTION long null_surface() { return -1; }
 #endif
 };
 
 //---------------------------------------------------------------------------//
 // INLINE DEFINITIONS
 //---------------------------------------------------------------------------//
 /*!
  * Construct from persistent and state data.
  */
 CELER_FUNCTION
 VecgeomTrackView::VecgeomTrackView(ParamsRef const& params,
                                    StateRef const& states,
                                    TrackSlotId tid)
     : params_(params)
     , vgstate_(states.vgstate.at(params_.max_depth, tid))
     , vgnext_(states.vgnext.at(params_.max_depth, tid))
     , pos_(states.pos[tid])
     , dir_(states.dir[tid])
 #ifdef VECGEOM_USE_SURF
     , next_surface_{states.next_surface[tid]}
 #endif
 {
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Construct the state.
  *
  * Expensive. This function should only be called to initialize an event from a
  * starting location and direction, but excess secondaries will also be
  * initialized this way.
  */
 CELER_FUNCTION VecgeomTrackView&
 VecgeomTrackView::operator=(Initializer_t const& init)
 {
     CELER_EXPECT(is_soft_unit_vector(init.dir));
 
     // Initialize position/direction
     pos_ = init.pos;
     dir_ = init.dir;
 #ifdef VECGEOM_USE_SURF
     next_surface_ = null_surface();
 #endif
 
     // Set up current state and locate daughter volume.
     vgstate_.Clear();
     constexpr bool contains_point = true;
 #ifdef VECGEOM_USE_SURF
     auto world = vecgeom::NavigationState::WorldId();
 #else
     vecgeom::VPlacedVolume const* world = params_.world_volume;
 #endif
     // LocatePointIn sets `vgstate_`
     Navigator::LocatePointIn(
         world, detail::to_vector(pos_), vgstate_, contains_point);
     return *this;
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Construct the state from a direction and a copy of the parent state.
  *
  * This is a faster method of creating secondaries from a parent that has just
  * been absorbed, or when filling in an empty track from a parent that is still
  * alive.
  */
 CELER_FUNCTION
 VecgeomTrackView& VecgeomTrackView::operator=(DetailedInitializer const& init)
 {
     CELER_EXPECT(is_soft_unit_vector(init.dir));
 
     if (this != &init.other)
     {
         // Copy the navigation state and position from the parent state
         init.other.vgstate_.CopyTo(&vgstate_);
         pos_ = init.other.pos_;
     }
 
     // Set up the next state and initialize the direction
     vgnext_ = vgstate_;
     dir_ = init.dir;
 
     CELER_ENSURE(!this->has_next_step());
     return *this;
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Get the volume ID in the current cell.
  */
 CELER_FORCEINLINE_FUNCTION VolumeId VecgeomTrackView::volume_id() const
 {
     CELER_EXPECT(!this->is_outside());
     return id_cast<VolumeId>(this->volume().id());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Get the physical volume ID in the current cell.
  */
 CELER_FUNCTION VolumeInstanceId VecgeomTrackView::volume_instance_id() const
 {
     CELER_EXPECT(!this->is_outside());
     vecgeom::VPlacedVolume const* top = vgstate_.Top();
     CELER_ASSERT(top);
     return id_cast<VolumeInstanceId>(top->id());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Get the depth in the geometry hierarchy.
  */
 CELER_FUNCTION LevelId VecgeomTrackView::level() const
 {
     return id_cast<LevelId>(vgstate_.GetLevel());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Get the volume instance ID for all levels>
  */
 CELER_FUNCTION void
 VecgeomTrackView::volume_instance_id(Span<VolumeInstanceId> levels) const
 {
     CELER_EXPECT(levels.size() == this->level().get() + 1);
     for (auto lev : range(levels.size()))
     {
         vecgeom::VPlacedVolume const* pv = vgstate_.At(lev);
         CELER_ASSERT(pv);
         levels[lev] = id_cast<VolumeInstanceId>(vgstate_.At(lev)->id());
     }
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Whether the track is outside the valid geometry region.
  */
 CELER_FUNCTION bool VecgeomTrackView::is_outside() const
 {
     return vgstate_.IsOutside();
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Whether the track is on the boundary of a volume.
  */
 CELER_FUNCTION bool VecgeomTrackView::is_on_boundary() const
 {
     return vgstate_.IsOnBoundary();
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Find the distance to the next geometric boundary.
  *
  * This function is allowed to be called from the exterior for ray tracing.
  */
 CELER_FUNCTION Propagation VecgeomTrackView::find_next_step()
 {
     if (this->is_outside())
     {
         // SPECIAL CASE: find distance to interior from outside world volume
         auto* pplvol = params_.world_volume;
         next_step_ = pplvol->DistanceToIn(detail::to_vector(pos_),
                                           detail::to_vector(dir_),
                                           vecgeom::kInfLength);
 
         next_step_ = max(next_step_, this->extra_push());
         vgnext_.Clear();
         Propagation result;
         result.distance = next_step_;
         result.boundary = next_step_ < vecgeom::kInfLength;
 
         if (result.boundary)
         {
             vgnext_.Push(pplvol);
             vgnext_.SetBoundaryState(true);
         }
 
         return result;
     }
 
     return this->find_next_step(vecgeom::kInfLength);
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Find the distance to the next geometric boundary.
  */
 CELER_FUNCTION Propagation VecgeomTrackView::find_next_step(real_type max_step)
 {
     CELER_EXPECT(!this->is_outside());
     CELER_EXPECT(max_step > 0);
 
 #ifdef VECGEOM_USE_SURF
     // Use the navigator to find internal distance
     next_surface_ = null_surface();
 #endif
     // TODO: vgnext is simply copied and the boundary flag optionally set
     next_step_ = Navigator::ComputeStepAndNextVolume(detail::to_vector(pos_),
                                                      detail::to_vector(dir_),
                                                      max_step,
                                                      vgstate_,
                                                      vgnext_
 #ifdef VECGEOM_USE_SURF
                                                      ,
                                                      next_surface_
 #endif
     );
     next_step_ = max(next_step_, this->extra_push());
 
     if (!this->is_next_boundary())
     {
         // Soft equivalence between distance and max step is because the
         // BVH navigator subtracts and then re-adds a bump distance to the
         // step
         CELER_ASSERT(soft_equal(next_step_, max_step));
         next_step_ = max_step;
     }
 
     Propagation result;
     result.distance = next_step_;
     result.boundary = this->is_next_boundary();
 
     CELER_ENSURE(this->has_next_step());
     CELER_ENSURE(result.distance > 0);
     CELER_ENSURE(result.distance <= max(max_step, this->extra_push()));
     CELER_ENSURE(result.boundary || result.distance == max_step
                  || max_step < this->extra_push());
     return result;
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Find the safety at the current position.
  */
 CELER_FUNCTION real_type VecgeomTrackView::find_safety()
 {
     return this->find_safety(vecgeom::kInfLength);
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Find the safety at the current position up to a maximum distance.
  *
  * The safety within a step is only needed up to the end of the physics step
  * length.
  */
 CELER_FUNCTION real_type VecgeomTrackView::find_safety(real_type max_radius)
 {
     CELER_EXPECT(!this->is_outside());
     CELER_EXPECT(!this->is_on_boundary());
     CELER_EXPECT(max_radius > 0);
 
     real_type safety = Navigator::ComputeSafety(detail::to_vector(this->pos()),
                                                 vgstate_
 #if VECGEOM_VERSION >= 0x200000
                                                 ,
                                                 max_radius
 #endif
     );
     safety = min<real_type>(safety, max_radius);
 
     // Since the reported "safety" is negative if we've moved slightly beyond
     // the boundary of a solid without crossing it, we must clamp to zero.
     return max<real_type>(safety, 0);
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Move to the next boundary but don't cross yet.
  */
 CELER_FUNCTION void VecgeomTrackView::move_to_boundary()
 {
     CELER_EXPECT(this->has_next_step());
     CELER_EXPECT(this->is_next_boundary());
 
     // Move next step
     axpy(next_step_, dir_, &pos_);
     next_step_ = 0;
     vgstate_.SetBoundaryState(true);
 
     CELER_ENSURE(this->is_on_boundary());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Cross from one side of the current surface to the other.
  *
  * The position *must* be on the boundary following a move-to-boundary.
  */
 CELER_FUNCTION void VecgeomTrackView::cross_boundary()
 {
     CELER_EXPECT(this->is_on_boundary());
     CELER_EXPECT(this->is_next_boundary());
 
     // Relocate to next tracking volume (maybe across multiple boundaries)
     if (vgnext_.Top() != nullptr)
     {
 #ifdef VECGEOM_USE_SURF
         if (!vgstate_.IsOutside())
         {
             // In surf model, relocation does not work from [OUTSIDE]
             // (no need to call this function) as vgnext_ is already set
             Navigator::RelocateToNextVolume(detail::to_vector(this->pos_),
                                             detail::to_vector(this->dir_),
                                             next_surface_,
                                             vgnext_);
         }
 #else
         // Some navigators require an lvalue temp_pos
         auto temp_pos = detail::to_vector(this->pos_);
         Navigator::RelocateToNextVolume(
             temp_pos, detail::to_vector(this->dir_), vgnext_);
 #endif
     }
 
     vgstate_ = vgnext_;
 
     CELER_ENSURE(this->is_on_boundary());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Move within the current volume.
  *
  * The straight-line distance *must* be less than the distance to the
  * boundary.
  */
 CELER_FUNCTION void VecgeomTrackView::move_internal(real_type dist)
 {
     CELER_EXPECT(this->has_next_step());
     CELER_EXPECT(dist > 0 && dist <= next_step_);
     CELER_EXPECT(dist != next_step_ || !this->is_next_boundary());
 
     // Move and update next_step_
     axpy(dist, dir_, &pos_);
     next_step_ -= dist;
     vgstate_.SetBoundaryState(false);
 
     CELER_ENSURE(!this->is_on_boundary());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Move within the current volume to a nearby point.
  *
  * \warning It's up to the caller to make sure that the position is
  * "nearby" and within the same volume.
  */
 CELER_FUNCTION void VecgeomTrackView::move_internal(Real3 const& pos)
 {
     pos_ = pos;
     next_step_ = 0;
     vgstate_.SetBoundaryState(false);
 
     CELER_ENSURE(!this->is_on_boundary());
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Change the track's direction.
  *
  * This happens after a scattering event or movement inside a magnetic field.
  * It resets the calculated distance-to-boundary.
  */
 CELER_FUNCTION void VecgeomTrackView::set_dir(Real3 const& newdir)
 {
     CELER_EXPECT(is_soft_unit_vector(newdir));
     dir_ = newdir;
     next_step_ = 0;
 }
 
 //---------------------------------------------------------------------------//
 // PRIVATE MEMBER FUNCTIONS
 //---------------------------------------------------------------------------//
 /*!
  * Whether a next step has been calculated.
  */
 CELER_FUNCTION bool VecgeomTrackView::has_next_step() const
 {
     return next_step_ != 0;
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Whether the calculated next step will take track to next boundary.
  */
 CELER_FUNCTION bool VecgeomTrackView::is_next_boundary() const
 {
     CELER_EXPECT(this->has_next_step() || this->is_on_boundary());
     return vgnext_.IsOnBoundary();
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Get a reference to the current volume, or to world volume if outside.
  */
 CELER_FUNCTION auto VecgeomTrackView::volume() const -> Volume const&
 {
     vecgeom::VPlacedVolume const* physvol_ptr = vgstate_.Top();
     CELER_ENSURE(physvol_ptr);
     return *physvol_ptr->GetLogicalVolume();
 }
 
 //---------------------------------------------------------------------------//
 }  // namespace celeritas

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