Make opencv2.xcframework for iOS arm64, and iOSSimulator arm64 & x86_64

make-opencv2-xcframework.md

I had some trouble attempting to build an XCFramework of OpenCV, but I finally got a successful build with the following steps:

1. Clone the OpenCV repo:

   git clone git@github.com:opencv/opencv.git
   cd opencv
   

2. Disable building with libjpeg-turbo¹ by applying a patch:

   git apply path/to/opencv-5-28-50.patch

3. Make a build directory adjacent to the opencv repo

   cd ..
   mkdir build-opencv
   cd build-opencv

4. Build the xcframework (change these options per your requirements):

   python3 ../opencv/platforms/apple/build_xcframework.py \
     --out . \
     --without=video \
     --iphoneos_archs=arm64 \
     --iphonesimulator_archs x86_64,arm64 \
     --iphoneos_deployment_target=13 \
     --disable-bitcode \
     --build_only_specified_archs

If all goes well, after quite some time you should see:

============================================================
Finished building ./opencv2.xcframework
============================================================

Footnotes

1. Why do we need to disable libjpeg-turbo? Because it fails to build during the configuration stage with:

   -- libjpeg-turbo: VERSION = 2.1.2, BUILD = opencv-4.6.0-libjpeg-turbo
   -- Check size of size_t
   CMake Error at /usr/local/share/cmake-3.25/Modules/CheckTypeSize.cmake:148 (try_compile):
     Cannot copy output executable
   
       ''
   
     to destination specified by COPY_FILE:
   
       'opencv-build-ios13/iphoneos/build/build-arm64-iphoneos/CMakeFiles/CheckTypeSize/SIZEOF_SIZE_T.bin'
   
     Recorded try_compile output location doesn't exist:
   
       opencv-build-ios13/iphoneos/build/build-arm64-iphoneos/CMakeFiles/CMakeScratch/TryCompile-kqujHS/Release/cmTC_afcdc.app/cmTC_afcdc
   
   Call Stack (most recent call first):
     /usr/local/share/cmake-3.25/Modules/CheckTypeSize.cmake:278 (__check_type_size_impl)
     3rdparty/libjpeg-turbo/CMakeLists.txt:25 (check_type_size)
   
   
   -- Check size of unsigned long
   CMake Error at /usr/local/share/cmake-3.25/Modules/CheckTypeSize.cmake:148 (try_compile):
     Cannot copy output executable
   
       ''
   
     to destination specified by COPY_FILE:
   
       'opencv-build-ios13/iphoneos/build/build-arm64-iphoneos/CMakeFiles/CheckTypeSize/SIZEOF_UNSIGNED_LONG.bin'
   
     Recorded try_compile output location doesn't exist:
   
       opencv-build-ios13/iphoneos/build/build-arm64-iphoneos/CMakeFiles/CMakeScratch/TryCompile-Mi900g/Release/cmTC_68bed.app/cmTC_68bed
   
   Call Stack (most recent call first):
     /usr/local/share/cmake-3.25/Modules/CheckTypeSize.cmake:278 (__check_type_size_impl)
     3rdparty/libjpeg-turbo/CMakeLists.txt:26 (check_type_size)
   

   I'm not sure what the consequences are of this change, so use at your own risk! ↩

opencv-5-28-50-PM.patch

diff --git forkSrcPrefix/platforms/ios/build_framework.py forkDstPrefix/platforms/ios/build_framework.py
index 08d9fd63dc8e2cbc77358b2e5f92e1ad2672b890..26d89b47a90823a03b490257e4674bdc40d03e46 100755
--- forkSrcPrefix/platforms/ios/build_framework.py
+++ forkDstPrefix/platforms/ios/build_framework.py
@@ -106,7 +106,7 @@ class Builder:
             main_build_dir = self.getBuildDir(main_working_dir, target)
             dirs.append(main_build_dir)
 
-            cmake_flags = []
+            cmake_flags = ["-DBUILD_JPEG_TURBO_DISABLE=ON"]
             if self.contrib:
                 cmake_flags.append("-DOPENCV_EXTRA_MODULES_PATH=%s" % self.contrib)
             if xcode_ver >= 7 and target[1] == 'iPhoneOS' and self.bitcodedisabled == False:

opencv2-4.6.0-ios13.xcframework.zip

By reading the following
opencv/opencv#21571
https://github.com/opencv/opencv/tree/4.x/platforms/apple

The above problem is solved by

python3 ../opencv/platforms/apple/build_xcframework.py \
  --out . \
  --without=video \
  --iphoneos_archs=arm64 \
  --iphonesimulator_archs=arm64 \
  --iphoneos_deployment_target=17 \
  --disable-bitcode \
  --build_only_specified_archs

The --iphonesimulator_archs=amr64 was --iphonesimulator_archs x86_64,arm64. The difference is using = and only specifying arm64.