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Add support for VecGeom v2 #15737

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68 changes: 62 additions & 6 deletions Detectors/Base/src/GeometryManager.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@

#ifdef O2_WITH_VECGEOM
#include "TGeo2VecGeom/RootGeoManager.h"
#include <VecGeom/base/Version.h>
#include <VecGeom/management/GeoManager.h>
#include <VecGeom/management/ABBoxManager.h>
#include <VecGeom/management/BVHManager.h>
Expand All @@ -40,7 +41,11 @@
#include <VecGeom/navigation/NewSimpleNavigator.h>
#include <VecGeom/navigation/BVHNavigator.h>
#include <VecGeom/navigation/SimpleLevelLocator.h>
#if VECGEOM_VERSION >= 0x020000
#include <VecGeom/navigation/SimpleABBoxLevelLocator.h>
#else
#include <VecGeom/navigation/BVHLevelLocator.h>
#endif
#include <VecGeom/navigation/VNavigator.h>
#include <VecGeom/volumes/LogicalVolume.h>
#include <mutex>
Expand Down Expand Up @@ -557,6 +562,14 @@ void GeometryManager::loadGeometry(std::string_view simPrefix, bool applyMisalig

namespace
{
/// Volumes with very few daughters are cheaper to brute-force than to accelerate. Defined once
/// because two places must agree on it: where the navigators and locators are attached below,
/// and where vecGeomMaterialBudget() decides how to take a step.
bool usesBvhAcceleration(vecgeom::LogicalVolume const* vol)
{
return vol->GetDaughtersp()->size() > 2;
}

/// Converts the currently loaded TGeo geometry to VecGeom and sets up navigators, once per
/// process, the first time the VecGeom backend is requested. Not part of loadGeometry(),
/// which every job calls regardless of whether it ever uses the VecGeom backend.
Expand All @@ -578,16 +591,35 @@ void ensureVecGeomWorldBuilt()
vecgeom::BVHManager::Init();

// For each logical volume, set both a navigator (used for ComputeStep) and a matched
// level locator (used for point relocation after a boundary crossing via GlobalLocator);
// volumes with very few daughters are cheaper to brute-force than to accelerate.
// level locator (used for point relocation after a boundary crossing via GlobalLocator).
for (auto& lvol : vecgeom::GeoManager::Instance().GetLogicalVolumesMap()) {
auto* vol = lvol.second;
if (vol->GetDaughtersp()->size() <= 2) {
if (!usesBvhAcceleration(vol)) {
vol->SetNavigator(vecgeom::NewSimpleNavigator<>::Instance());
vol->SetLevelLocator(vecgeom::SimpleLevelLocator::GetInstance());
} else {
#if VECGEOM_VERSION >= 0x020000
// VecGeom 2 turned BVHNavigator into a plain class with static entry points instead of a
// VNavigator singleton, so there is nothing to attach: vecGeomMaterialBudget() calls it
// directly.
//
// The locator changes too, and not by choice. BVHLevelLocator does not compile in 2.1.0 or
// 2.1.1 -- the header is byte-identical in both -- because its four LevelLocate() calls
// have no match among the single templated BVH::LevelLocate(int exclude_item_id, ...) that
// v2 ships. It survived two releases because nothing in VecGeom includes that header
// except itself, so upstream CI never compiles it; O2 appears to be its only consumer.
//
// SimpleABBoxLevelLocator is the accelerated stand-in, using the ABBoxes built just above.
// Three of the four methods could be rebuilt on the templated API (the idiom is in
// BVHNavigator itself: bvh->LevelInside<BVHNavigator>(exclude_id, point, id, dlp)), but
// the direction-aware LevelLocateExclVol has no v2 counterpart at all, so this stays a
// fallback rather than a reimplementation. Revert to BVHLevelLocator once upstream fixes
// or removes it, and measure: whether ABBox location costs anything real here is unknown.
vol->SetLevelLocator(vecgeom::SimpleABBoxLevelLocator::GetInstance());
#else
vol->SetNavigator(vecgeom::BVHNavigator<>::Instance());
vol->SetLevelLocator(vecgeom::BVHLevelLocator::GetInstance());
#endif
}
}
});
Expand All @@ -614,9 +646,24 @@ o2::base::MatBudget GeometryManager::vecGeomMaterialBudget(float x0, float y0, f
dir[i] *= invlen;
}

// Only the allocation differs between VecGeom versions; everything below works on pointers in
// both, which also keeps the std::swap() at the end of the loop a pointer swap rather than a
// copy of the state itself.
//
// VecGeom 1 builds NavigationState as NavStatePath, a variable-size object that must be told the
// maximum depth at construction and can only be made through MakeInstance(). VecGeom 2 dropped
// NavStatePath and MakeInstance with it: NavigationState is NavStateIndex or NavStateTuple, both
// fixed-size value types, so a thread_local object is the direct equivalent.
#if VECGEOM_VERSION >= 0x020000
thread_local static vecgeom::NavigationState newnavstateStorage, currnavstateStorage, startCacheStorage;
thread_local static vecgeom::NavigationState* newnavstate = &newnavstateStorage;
thread_local static vecgeom::NavigationState* currnavstate = &currnavstateStorage;
thread_local static vecgeom::NavigationState* startCache = &startCacheStorage;
#else
thread_local static vecgeom::NavigationState* newnavstate = vecgeom::NavigationState::MakeInstance(vecgeom::GeoManager::Instance().getMaxDepth());
thread_local static vecgeom::NavigationState* currnavstate = vecgeom::NavigationState::MakeInstance(vecgeom::GeoManager::Instance().getMaxDepth());
thread_local static vecgeom::NavigationState* startCache = vecgeom::NavigationState::MakeInstance(vecgeom::GeoManager::Instance().getMaxDepth());
#endif
thread_local static bool startCacheValid = false;

Vector3D currPoint(x0, y0, z0);
Expand Down Expand Up @@ -649,9 +696,18 @@ o2::base::MatBudget GeometryManager::vecGeomMaterialBudget(float x0, float y0, f
Int_t nzero = 0;
while (remainingDist > 1.E-10) {
auto* lvol = currnavstate->Top()->GetLogicalVolume();
accountMaterial(static_cast<TGeoMaterial*>(lvol->GetMaterialPtr()), budStep);
vecgeom::VNavigator const* navigator = lvol->GetNavigator();
double step = static_cast<double>(navigator->ComputeStepAndPropagatedState(currPoint, dirr, remainingDist, *currnavstate, *newnavstate));
// Not LogicalVolume::GetMaterialPtr(): VecGeom 2 dropped the material slot from the logical
// volume. TGeo2VecGeom keeps what its conversion hook returned, indexed by logical volume id,
// and serves it for both VecGeom versions.
accountMaterial(static_cast<TGeoMaterial*>(tgeo2vecgeom::RootGeoManager::Instance().GetMaterialPtr(lvol)), budStep);
#if VECGEOM_VERSION >= 0x020000
const double step =
usesBvhAcceleration(lvol)
? static_cast<double>(vecgeom::BVHNavigator::ComputeStepAndPropagatedState(currPoint, dirr, remainingDist, *currnavstate, *newnavstate))
: static_cast<double>(lvol->GetNavigator()->ComputeStepAndPropagatedState(currPoint, dirr, remainingDist, *currnavstate, *newnavstate));
#else
const double step = static_cast<double>(lvol->GetNavigator()->ComputeStepAndPropagatedState(currPoint, dirr, remainingDist, *currnavstate, *newnavstate));
#endif
if (step < 2.E-10) {
nzero++;
} else {
Expand Down