Recently I’m trying to test if dlib could also work well in Xcode, so I want to memo some troubleshooting what I met at here.

Build Static Library

For using it, we could download the source code from dlib github. Then follow these steps to compile it.

cd examples
mkdir build && cd build
cmake -D BUILD_SHARED_LIBS=ON -G Xcode ..
cmake --build . --config Release

Next, come to “./examples/build/dlib_build”, there will be a generated Xcode project there. By changing this project settings to what we want, ex: platforms -> iOS, iOS Deployment Target -> iOS 12.0.

Set the running target to Any iOS Device for building arm static library.

Set the running target to any simulator, ex: iPhone XR for building x86 static library.

We could find the libraries under “./examples/build/dlib_build/Debug-iphoneos” & “./examples/build/dlib_build/Debug-iphonesimulator”.

Add Static Library into project

• Create a directory, ex: “Dlib”. Add files of “./dlib”, “./examples/build/dlib_build/Debug-iphoneos”, “./examples/build/dlib_build/Debug-iphonesimulator” into this folder.
• Drag “Dlib” folder, into project. Remove project reference of “./dlib”, “./examples/build/dlib_build/Debug-iphoneos”, “./examples/build/dlib_build/Debug-iphonesimulator”. Note: only remove reference, this should be same as only add files into project directory.
• Add Build Settings -> HEADER_SEARCH_PATH: $(PROJECT_DIR)/TestProject/Dlib
• Add Build Settings -> OTHER_FLAGS: -l"dlib"
• Add Build Settings -> OTHER_CFLAGS: -DNDEBUG -DDLIB_JPEG_SUPPORT -DDLIB_USE_BLAS -DDLIB_USE_LAPACK -DLAPACK_FORCE_UNDERSCORE
• Add Build Settings -> SWIFT_OBJC_BRIDGING_HEADER: TestProject/TestProject-Bridging-Header.h.I plan to use Swift as project language, so I need to create TestProject-Bridging-Header.h for compiling ObjectiveC++.
• Set Apple Clang - Code Generation -> Optimization Level Debug env as Fastest, Samallest[-Os]. This used for quick building the project. After debugging, we could change it back to None[-O0]
• Link Framework: Accelerate.framework, libdlib.a. The libdlib.a should be the universal static library, which could be generated by previous downloaded 2 static libraries:

    cd into TestProject/Dlib
    mkdir Lib-universallib
    xcrun -sdk iphoneos lipo -create Debug-iphoneos/libdlib.a Debug-iphonesimulator/libdlib.a -output Lib-universallib/libdlib.a
  

• Add the dlib wrapper ObjectiveC++ code, and add header into TestProject/TestProject-Bridging-Header.h

🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉

Troubleshooting

Undefined symbol

It seems everything goes well when I test the face landmark detection, however, when I try to test some dnn models, ex: dog_hipsterizer, it throws me these errors ⬇️

Undefined symbol: dlib::tt::affine_transform(dlib::tensor&, dlib::tensor const&, dlib::tensor const&, dlib::tensor const&)
Undefined symbol: dlib::tt::affine_transform_conv(dlib::tensor&, dlib::tensor const&, dlib::tensor const&, dlib::tensor const&)
Undefined symbol: dlib::cpu::tensor_conv::operator()(bool, dlib::resizable_tensor&. dlib::tensor const&, dlib::tensor const&)
Undefined symbol: dlib::tt::add(float, dlib::tensor&, float, dlib::tensor const&)
Undefined symbol: dlib::tt::relu(dlib::tensor&, dlib::tensor const&)
Undefined symbol: dlib::tt::resize_bilinear(dlib::tensor&, long, long, dlib::tensor const&, long, long)

Solution: After researching, this might be the library link issue. I’m compiling dlib into 2 static library: iphoneos & iphonesimulator. And I link these 2 libraries by adding them in the Build Settings -> Library Search Paths by setting as $(PROJECT_DIR)/TestProject/Dlib/Debug$(EFFECTIVE_PLATFORM_NAME) for switch compiling lib automatically. But it seems it cannot work well for the dog_hipsterizer one which are using some cuda libraries. So I switch to use the universal static library for this part.

Reference

• http://dlib.net/
• https://github.com/davisking/dlib