Fix build against nanoflann >= 1.10 and SYCL+GCC libomp linkage

[MGRAFF2006]

Description

Two small, independent build fixes needed to compile AliceVision (develop) against current toolchains/dependencies. Both are isolated and behavior-preserving.

1. fix(deps): expose IndexType in custom nanoflann result sets

nanoflann 1.10.0 casts the accessor to typename RESULTSET::IndexType in KDTreeBaseClass::searchLevel():

if (!result_set.addPoint(
        static_cast<typename RESULTSET::DistanceType>(dist),
        static_cast<typename RESULTSET::IndexType>(accessor)))   // <-- requires IndexType typedef

Two custom result-set classes only carried IndexType as a template parameter and did not publish it as a member typedef, so building against nanoflann ≥ 1.10 fails with:

error: no type named 'IndexType' in 'class aliceVision::fuseCut::SmallerPixSizeInRadius<double, long unsigned int>'
error: no type named 'IndexType' in 'class BestPointInRadius<double, long unsigned int>'

Fix: rename the template parameter to _IndexType and expose using IndexType = _IndexType; (mirroring the existing DistanceType typedef added for nanoflann 1.7). No behavior change.

Affected files:

• src/aliceVision/fuseCut/Kdtree.hpp (SmallerPixSizeInRadius)
• src/software/convert/main_importE57.cpp (BestPointInRadius)

2. fix(cmake): link libomp by full path for SYCL libraries built with GCC

When AliceVision is built with GCC but the SYCL depthmap sources are compiled by AdaptiveCpp/clang (-fopenmp), the resulting aliceVision_depthMap_sycl library depends on LLVM's OpenMP runtime (libomp, __kmpc_* symbols). The existing target_link_options(... "-lomp") does not reliably propagate to GCC-linked consumers, so linking executables fails:

libaliceVision_depthMap_sycl.so: undefined reference to `__kmpc_fork_call'
libaliceVision_depthMap_sycl.so: undefined reference to `__kmpc_push_num_threads'
libaliceVision_depthMap_sycl.so: undefined reference to `__kmpc_global_thread_num'

Fix: resolve libomp to a full path (searching the AdaptiveCpp/ROCm LLVM lib dirs via AdaptiveCpp_DIR / ROCM_PATH when available) and link it with target_link_libraries(... PUBLIC ...) so it propagates transitively. Falls back to -lomp if not found.

Affected file:

• src/cmake/Helpers.cmake

Testing

Built develop end-to-end on Arch Linux (GCC 16, nanoflann 1.10.1, AdaptiveCpp 25.10 + ROCm 7.2, SYCL depthmap backend) — full build now completes and produces working aliceVision_* binaries including aliceVision_depthMapEstimation.

Notes

Marking as draft for maintainer review; happy to adjust the libomp discovery logic if there's a preferred pattern already used elsewhere in the CMake.

[gemini-code-assist]

Code Review

This pull request updates nanoflann-related classes in Kdtree.hpp and main_importE57.cpp to support nanoflann 1.10.0 by exposing the IndexType typedef. It also enhances the CMake build system to locate and explicitly link LLVM's OpenMP runtime (libomp) when compiling with GCC and SYCL. The review feedback suggests avoiding reserved C++ identifiers starting with an underscore and an uppercase letter, utilizing the exposed IndexType directly in member function signatures, and properly initializing the CMake hints list to prevent empty string entries from affecting find_library.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

In C++, identifiers starting with an underscore followed by an uppercase letter (such as _DistanceType and _IndexType) are reserved for the implementation in any scope. To avoid potential collisions with compiler internals or standard library headers, it is highly recommended to use standard names like DistanceT and IndexT for template parameters.

Suggested change

	template<typename _DistanceType, typename _IndexType = size_t>
	class SmallerPixSizeInRadius
	{
	public:
	// Necessary since nanoflann 1.7.0: https://github.com/jlblancoc/nanoflann/commit/9c84c4c32c2bfa7077cc8873dd3b5bcbb557da90
	using DistanceType = _DistanceType;
	// Necessary since nanoflann 1.10.0: result sets must expose an IndexType typedef
	using IndexType = _IndexType;
	template<typename DistanceT, typename IndexT = size_t>
	class SmallerPixSizeInRadius
	{
	public:
	// Necessary since nanoflann 1.7.0: https://github.com/jlblancoc/nanoflann/commit/9c84c4c32c2bfa7077cc8873dd3b5bcbb557da90
	using DistanceType = DistanceT;
	// Necessary since nanoflann 1.10.0: result sets must expose an IndexType typedef
	using IndexType = IndexT;

[gemini-code-assist]

Since IndexType is now a public member typedef of the class, we can use it directly in the member function signature instead of the template parameter _IndexType. This is cleaner and avoids using reserved names with leading underscores.

Suggested change

	inline bool addPoint(DistanceType dist, _IndexType index)
	inline bool addPoint(DistanceType dist, IndexType index)

[gemini-code-assist]

In C++, identifiers starting with an underscore followed by an uppercase letter (such as _DistanceType and _IndexType) are reserved for the implementation in any scope. To avoid potential collisions with compiler internals or standard library headers, it is highly recommended to use standard names like DistanceT and IndexT for template parameters.

template<typename DistanceT, typename IndexT = size_t>
class BestPointInRadius
{
  public:
    // Necessary since nanoflann 1.7.0: https://github.com/jlblancoc/nanoflann/commit/9c84c4c32c2bfa7077cc8873dd3b5bcbb557da90
    using DistanceType = DistanceT;
    // Necessary since nanoflann 1.10.0: result sets must expose an IndexType typedef
    using IndexType = IndexT;

[gemini-code-assist]

Since IndexType is now a public member typedef of the class, we can use it directly in the member function signature instead of the template parameter _IndexType. This is cleaner and avoids using reserved names with leading underscores.

    inline bool addPoint(DistanceType dist, IndexType index)

[gemini-code-assist]

In CMake, set(VAR "") initializes the variable as a list containing a single empty string element "". When you later append elements using list(APPEND VAR ...), the list will start with an empty string, which can cause issues with commands like find_library that interpret empty strings as paths (often resolving to the current working directory). Using set(_acpp_omp_hints) properly initializes it as an empty list.

          set(_acpp_omp_hints)