From d9a6036a0719d4dc9795389d98d0bd0080e6b0e5 Mon Sep 17 00:00:00 2001
From: Hans Johnson <hans-johnson@uiowa.edu>
Date: Sun, 7 Jun 2026 12:02:23 -0500
Subject: [PATCH] ENH: Modernize CUDA wiring and auto-detect default VKFFT
 backend

* itk-module-init.cmake: replace removed find_package(CUDA) with
  enable_language(CUDA) + find_package(CUDAToolkit). Auto-pick a
  default VKFFT_BACKEND when not set: CUDA if a CUDA compiler is
  found, Metal if the Apple Metal/Foundation/QuartzCore frameworks
  probe successfully, otherwise OpenCL.
* itk-module-init.cmake: handle VKFFT_BACKEND=5 (Metal) by locating
  the required Apple frameworks early.
* src/CMakeLists.txt: link CUDA::cuda_driver instead of the bare
  'cuda' name so conda/cross toolchains that do not search
  /usr/lib/x86_64-linux-gnu resolve libcuda.
* CMakeLists.txt: pull the vendored VkFFT sources with
  EXCLUDE_FROM_ALL so the upstream VkFFT_TestSuite benchmark (which
  hard-requires CL/cl.h and vulkan/vulkan.h) is not built unless
  explicitly requested.

Assisted-by: Claude Code (claude-opus-4-7) -- CMake modernization and Metal auto-detect branch.
---
 CMakeLists.txt        |  6 +++++-
 itk-module-init.cmake | 37 ++++++++++++++++++++++++++++++++++---
 src/CMakeLists.txt    |  2 +-
 3 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd698f3f..344aef41 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -137,7 +137,11 @@ if(BUILD_VKFFT)
     GIT_REPOSITORY ${VkFFT_GIT_REPOSITORY}
     GIT_TAG ${VkFFT_GIT_TAG}
     )
-  FetchContent_MakeAvailable(vkfft_lib)
+  FetchContent_GetProperties(vkfft_lib)
+  if(NOT vkfft_lib_POPULATED)
+    FetchContent_Populate(vkfft_lib)
+    add_subdirectory(${vkfft_lib_SOURCE_DIR} ${vkfft_lib_BINARY_DIR} EXCLUDE_FROM_ALL)
+  endif()
 
   set(vkfft_INCLUDE_DIR "${vkfft_lib_SOURCE_DIR}/vkFFT")
 else()
diff --git a/itk-module-init.cmake b/itk-module-init.cmake
index 8975ddc2..ac65fbe3 100644
--- a/itk-module-init.cmake
+++ b/itk-module-init.cmake
@@ -1,10 +1,34 @@
 #
 # Find the packages required by this module
 #
-set(VKFFT_BACKEND 3 CACHE STRING "1 - CUDA, 3 - OpenCL, 4 - Level Zero, 5 - Metal")
+if(NOT DEFINED VKFFT_BACKEND)
+  include(CheckLanguage)
+  check_language(CUDA)
+  set(_vkfft_have_metal FALSE)
+  if(APPLE)
+    find_library(_vkfft_metal_probe Metal)
+    find_library(_vkfft_foundation_probe Foundation)
+    find_library(_vkfft_quartzcore_probe QuartzCore)
+    if(_vkfft_metal_probe AND _vkfft_foundation_probe AND _vkfft_quartzcore_probe)
+      set(_vkfft_have_metal TRUE)
+    endif()
+  endif()
+  if(CMAKE_CUDA_COMPILER)
+    set(_vkfft_backend_default 1)
+  elseif(_vkfft_have_metal)
+    set(_vkfft_backend_default 5)
+  else()
+    set(_vkfft_backend_default 3)
+  endif()
+else()
+  set(_vkfft_backend_default ${VKFFT_BACKEND})
+endif()
+set(VKFFT_BACKEND ${_vkfft_backend_default} CACHE STRING "1 - CUDA, 3 - OpenCL, 4 - Level Zero, 5 - Metal")
 if(${VKFFT_BACKEND} EQUAL 1)
-  find_package(CUDA 9.0 REQUIRED)
-  find_library(CUDA_NVRTC_LIB libnvrtc nvrtc HINTS "${CUDA_TOOLKIT_ROOT_DIR}/lib64" "${CUDA_TOOLKIT_ROOT_DIR}/lib/x64" "/usr/lib64" "/usr/local/cuda/lib64")
+  enable_language(CUDA)
+  find_package(CUDAToolkit REQUIRED)
+  set(CUDA_LIBRARIES CUDA::cudart)
+  find_library(CUDA_NVRTC_LIB libnvrtc nvrtc HINTS "${CUDAToolkit_LIBRARY_DIR}" "/usr/lib64" "/usr/local/cuda/lib64")
 elseif(${VKFFT_BACKEND} EQUAL 3)
   find_package(OpenCL REQUIRED)
 elseif(${VKFFT_BACKEND} EQUAL 4)
@@ -19,4 +43,11 @@ elseif(${VKFFT_BACKEND} EQUAL 4)
   if(NOT LevelZero_INCLUDE_DIR OR NOT LevelZero_LIBRARY)
     message(FATAL_ERROR "VKFFT_BACKEND=4 (Level Zero) requires the oneAPI Level Zero loader (ze_loader) and headers (level_zero/ze_api.h).")
   endif()
+elseif(${VKFFT_BACKEND} EQUAL 5)
+  if(NOT APPLE)
+    message(FATAL_ERROR "VKFFT_BACKEND=5 (Metal) requires Apple platforms (macOS/iOS, including Apple Silicon).")
+  endif()
+  find_library(METAL_FRAMEWORK Metal REQUIRED)
+  find_library(FOUNDATION_FRAMEWORK Foundation REQUIRED)
+  find_library(QUARTZCORE_FRAMEWORK QuartzCore REQUIRED)
 endif()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e5b97549..08ea03ae 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -7,7 +7,7 @@ set(VkFFTBackend_SRCS
 itk_module_add_library(VkFFTBackend ${VkFFTBackend_SRCS})
 
 if(${VKFFT_BACKEND} EQUAL 1)
-	target_link_libraries(VkFFTBackend PUBLIC ${CUDA_LIBRARIES} cuda ${CUDA_NVRTC_LIB} VkFFT half)
+	target_link_libraries(VkFFTBackend PUBLIC ${CUDA_LIBRARIES} CUDA::cuda_driver ${CUDA_NVRTC_LIB} VkFFT half)
   if(MSVC)
   else()
     set_source_files_properties(itkVkCommon.cpp PROPERTIES LANGUAGE CUDA)