Constant Detector, main branch (2025.08.15.) (#1127)

* Use constant access in device code for the tracking geometry.

* Make the device code use constant detector access.

* Make the test and benchmark code produce constant detector views.

* Make the example code produce constant detector views.

Author: krasznaa

benchmarks/cuda/toy_detector_cuda.cpp

@@ -69,7 +69,7 @@ BENCHMARK_DEFINE_F(ToyDetectorBenchmark, CUDA)(benchmark::State& state) {
                                                           async_copy, stream);
 
     // Copy detector to device
-    auto det_buffer = detray::get_buffer(det, device_mr, copy);
+    const auto det_buffer = detray::get_buffer(det, device_mr, copy);
     // Detector view object
     auto det_view = detray::get_data(det_buffer);
 

core/include/traccc/geometry/detector.hpp

@@ -1,6 +1,6 @@
 /** TRACCC library, part of the ACTS project (R&D line)
  *
- * (c) 2024 CERN for the benefit of the ACTS project
+ * (c) 2024-2025 CERN for the benefit of the ACTS project
  *
  * Mozilla Public License Version 2.0
  */
@@ -16,7 +16,34 @@
 #include <detray/detectors/telescope_metadata.hpp>
 #include <detray/detectors/toy_metadata.hpp>
 
+// VecMem include(s).
+#include <vecmem/containers/device_vector.hpp>
+
+// System include(s).
+#include <type_traits>
+
 namespace traccc {
+namespace details {
+
+/// Type used instead of @c detray::device_container_types
+///
+/// This is meant as a template for how @c detray::device_container_types should
+/// change. So that it would correctly reflect that all data access on a device
+/// is constant. Not modifying the detector's payload.
+///
+/// Also note that with all the types present in @c detray::container_types
+/// it's really only @c vector_type that is actually used by @c detray::detector
+/// at this point.
+///
+struct device_detector_container_types {
+
+    /// Vector type to use in device code
+    template <typename T>
+    using vector_type = vecmem::device_vector<std::add_const_t<T>>;
+
+};  // struct device_detector_container_types
+
+}  // namespace details
 
 /// Base struct for the different detector types supported by the project.
 template <typename metadata_t>
@@ -28,13 +55,11 @@ struct detector {
     /// Host type of the detector.
     using host = detray::detector<metadata_type, detray::host_container_types>;
     /// Device type of the detector.
-    using device =
-        detray::detector<metadata_type, detray::device_container_types>;
+    using device = detray::detector<metadata_type,
+                                    details::device_detector_container_types>;
 
     /// Non-const view of the detector.
-    using view = typename host::view_type;
-    /// Const view of the detector.
-    using const_view = typename host::const_view_type;
+    using view = typename host::const_view_type;
 
     /// Buffer for a detector's data.
     using buffer = typename host::buffer_type;

device/alpaka/include/traccc/alpaka/seeding/spacepoint_formation_algorithm.hpp

@@ -33,7 +33,7 @@ namespace traccc::alpaka {
 template <typename detector_t>
 class spacepoint_formation_algorithm
     : public algorithm<edm::spacepoint_collection::buffer(
-          const typename detector_t::view_type&,
+          const typename detector_t::const_view_type&,
           const measurement_collection_types::const_view&)>,
       public messaging {
 
@@ -57,7 +57,7 @@ class spacepoint_formation_algorithm
     ///         measurement
     ///
     edm::spacepoint_collection::buffer operator()(
-        const typename detector_t::view_type& det_view,
+        const typename detector_t::const_view_type& det_view,
         const measurement_collection_types::const_view& measurements_view)
         const override;
 

device/alpaka/src/finding/combinatorial_kalman_filter.hpp

@@ -198,7 +198,7 @@ struct build_tracks {
 template <typename detector_t, typename bfield_t>
 edm::track_candidate_collection<default_algebra>::buffer
 combinatorial_kalman_filter(
-    const typename detector_t::view_type& det, const bfield_t& field,
+    const typename detector_t::const_view_type& det, const bfield_t& field,
     const measurement_collection_types::const_view& measurements,
     const bound_track_parameters_collection_types::const_view& seeds,
     const finding_config& config, const memory_resource& mr, vecmem::copy& copy,

device/alpaka/src/fitting/kalman_fitting.hpp

@@ -113,7 +113,8 @@ struct fit_backward {
 ///
 template <typename detector_t, typename bfield_t>
 track_state_container_types::buffer kalman_fitting(
-    const typename detector_t::view_type& det_view, const bfield_t& field_view,
+    const typename detector_t::const_view_type& det_view,
+    const bfield_t& field_view,
     const typename edm::track_candidate_container<
         typename detector_t::algebra_type>::const_view& track_candidates_view,
     const fitting_config& config, const memory_resource& mr, vecmem::copy& copy,

device/alpaka/src/seeding/spacepoint_formation_algorithm.cpp

@@ -22,7 +22,7 @@ template <typename detector_t>
 struct FormSpacepointsKernel {
     template <typename TAcc>
     ALPAKA_FN_ACC void operator()(
-        TAcc const& acc, typename detector_t::view_type det_view,
+        TAcc const& acc, typename detector_t::const_view_type det_view,
         measurement_collection_types::const_view measurements_view,
         edm::spacepoint_collection::view spacepoints_view) const {
 
@@ -43,7 +43,7 @@ spacepoint_formation_algorithm<detector_t>::spacepoint_formation_algorithm(
 template <typename detector_t>
 edm::spacepoint_collection::buffer
 spacepoint_formation_algorithm<detector_t>::operator()(
-    const typename detector_t::view_type& det_view,
+    const typename detector_t::const_view_type& det_view,
     const measurement_collection_types::const_view& measurements_view) const {
 
     // Get a convenience variable for the queue that we'll be using.

device/common/include/traccc/finding/device/apply_interaction.hpp

@@ -26,7 +26,7 @@ struct apply_interaction_payload {
     /**
      * @brief View object describing the tracking detector
      */
-    typename detector_t::view_type det_data;
+    typename detector_t::const_view_type det_data;
 
     /**
      * @brief Total number of input parameters (including non-live ones)

device/common/include/traccc/finding/device/find_tracks.hpp

@@ -34,7 +34,7 @@ struct find_tracks_payload {
     /**
      * @brief View object to the tracking detector description
      */
-    typename detector_t::view_type det_data;
+    typename detector_t::const_view_type det_data;
 
     /**
      * @brief View object to the vector of bound track parameters

device/common/include/traccc/finding/device/propagate_to_next_surface.hpp

@@ -28,7 +28,7 @@ struct propagate_to_next_surface_payload {
     /**
      * @brief View object to the tracking detector description
      */
-    typename propagator_t::detector_type::view_type det_data;
+    typename propagator_t::detector_type::const_view_type det_data;
 
     /**
      * @brief View object to the magnetic field

device/common/include/traccc/fitting/device/fit.hpp

@@ -26,7 +26,7 @@ struct fit_payload {
     /**
      * @brief View object to the detector description
      */
-    typename fitter_t::detector_type::view_type det_data;
+    typename fitter_t::detector_type::const_view_type det_data;
 
     /**
      * @brief View object to the magnetic field description