ExternallyAlignedDetectorElement.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2019 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/Definitions/Algebra.hpp"
#include "Acts/Geometry/GeometryContext.hpp"
#include "Acts/Geometry/GeometryIdentifier.hpp"
#include "Acts/Plugins/Identification/IdentifiedDetectorElement.hpp"
#include "Acts/Plugins/Identification/Identifier.hpp"
#include "Acts/Surfaces/Surface.hpp"
#include "ActsExamples/GenericDetector/GenericDetectorElement.hpp"

#include <map>

namespace ActsExamples {

namespace Contextual {

class ExternallyAlignedDetectorElement
    : public Generic::GenericDetectorElement {
 public:
  struct AlignmentStore {
    // GenericDetector identifiers are sequential
    std::vector<Acts::Transform3> transforms;
    size_t lastAccessed = 0;
  };

  struct ContextType {
    // GenericDetector identifiers are an integer sequence, so vector is fine!
    std::shared_ptr<const AlignmentStore> alignmentStore{nullptr};
  };

  using Generic::GenericDetectorElement::GenericDetectorElement;

  const Acts::Transform3& transform(
      const Acts::GeometryContext& gctx) const override;
};

inline const Acts::Transform3& ExternallyAlignedDetectorElement::transform(
    const Acts::GeometryContext& gctx) const {
  if (!gctx.hasValue()) {  // Treating empty context => nominal alignment
    return GenericDetectorElement::transform(gctx);
  }
  // cast into the right context object
  const auto& alignContext = gctx.get<ContextType>();
  identifier_type idValue = identifier_type(identifier());

  if (alignContext.alignmentStore == nullptr) {
    // geometry construction => nominal alignment
    return GenericDetectorElement::transform(gctx);
  }

  // At this point, the alignment store should be populated
  assert(idValue < alignContext.alignmentStore->transforms.size());
  return alignContext.alignmentStore->transforms[idValue];
}

}  // end of namespace Contextual
}  // end of namespace ActsExamples