libdartcv.dylib Not Found When Installing opencv_core Plugin (macOS)

[Kapustine]

Hello,
I'm excited to have discovered such a great plugin. However, I haven’t been able to use it yet.
I tried using the opencv_core plugin and followed the installation steps, but I encountered an error saying that the dylib could not be found. (I tried it on both Intel and ARM Macs.)

Key steps:

$ flutter create app
$ cd app
$ flutter pub add opencv_core
$ flutter pub get
$ cd macos
$ pod install

Runtime error:

✓ Built build/macos/Build/Products/Debug/app.app
Connecting to VM Service at ws://127.0.0.1:59948/C0WG2-o5bkA=/ws
Connected to the VM Service.
flutter: Error loading libdartcv.dylib, error: Invalid argument(s): Failed to load dynamic library 'libdartcv.dylib': dlopen(libdartcv.dylib, 0x0001): tried: 'libdartcv.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OSlibdartcv.dylib' (no such file), '/Users/hriver/Git/flopencv/app/build/macos/Build/Products/Debug/app.app/Contents/Frameworks/FlutterMacOS.framework/Versions/A/./libdartcv.dylib' (no such file), '/usr/local/lib/./libdartcv.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/usr/local/lib/./libdartcv.dylib' (no such file), '/Users/hriver/Git/flopencv/app/build/macos/Build/Products/Debug/app.app/Contents/Frameworks/FlutterMacOS.framework/Versions/A/../../../libdartcv.dylib' (no such file), '/usr/lib/swift/libdartcv.dylib' (no such file, not in dyld cache), '/System/Volumes/Preboot/Cryptexes/OS/usr/lib/swift/libdartcv.dylib' (no such file), '/Users/hriver/Git/flopencv/app/build/macos/Build/Products/Debug/app.app/Contents/Frameworks/libdartcv.dylib' (no such file), '/Users/hriver/Git/flopencv/app/build/macos/Build/Products/Debug/app.app/Contents/MacOS/Frameworks/libdartcv.dylib' (no such file), '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libdartcv.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libdartcv.dylib' (no such file), '/usr/lib/libdartcv.dylib' (no such file, not in dyld cache), 'libdartcv.dylib' (no such file)
fallback to process.
.
.
.

Am I possibly missing an important step? I would really appreciate it if you could let me know if there’s anything else I should do. Thanks!

[rainyl]

@Kapustine Hello~

It's okay, for debug purpose, on macos, the package will firstly try to find libdartcv.dylib and then load from process, and if you are using Flutter, typically the native library will be statically linked to your program since it is introduced by cocoapods, therefore, ffi.DynamicLibrary.process() should work and you can use opencv functions as normal.

If something like symbol XXX not found is reported, please let me know.

[Kapustine]

Thank you very much for your prompt response.

To be honest, I did try running it under the previous conditions — and I ran into this error:

Exception has occurred. X  
CvException (CvException(code: -215, msg: OpenCV(4.11.0) /Users/runner/work/opencv.full/opencv.full/opencv/modules/imgproc/src/color.cpp:199: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor')

Here’s the code I was working with:

final path = "/path/to/sample.jpg";
if (File(path).existsSync()) {
    final mat = cv.imread(path);
    // heavy computation
    final (gray, blur) = await heavyTaskAsync(mat, count: 1);
    ...

Thanks to your response, however, I realized that the issue wasn’t with OpenCV or the plugin at all — it was on me!
I had forgotten to disable com.apple.security.app-sandbox. My apologies for the confusion!

While I have your attention, I’d also like to report a build warning and error I encountered:

--- xcodebuild: WARNING: Using the first of multiple matching destinations:
{ platform:macOS, arch:arm64, id:00006001-001420180E02801E, name:My Mac }
{ platform:macOS, arch:x86_64, id:00006001-001420180E02801E, name:My Mac }
warning: Run script build phase 'Create Symlinks to Header Folders' will be run during every build because it does not specify any outputs...
error: DT_TOOLCHAIN_DIR cannot be used to evaluate LIBRARY_SEARCH_PATHS, use TOOLCHAIN_DIR instead (in target 'opencv_core' from project 'Pods')
** BUILD FAILED **

As the message suggests, I was able to resolve this by editing the following line in:
macos/Pods/Target Support Files/opencv_core/opencv_core.release.xcconfig
— replacing "DT_TOOLCHAIN_DIR" with "TOOLCHAIN_DIR".

From what I looked into, it looks like this change came with Xcode 15.
Thank you again for your kind support.

[rainyl]

CvException (CvException(code: -215, msg: OpenCV(4.11.0) /Users/runner/work/opencv.full/opencv.full/opencv/modules/imgproc/src/color.cpp:199: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor')

aha, yes, any exceptions like this tend to be the incorrect calling of opencv or permission issues.

As the message suggests, I was able to resolve this by editing the following line in:
macos/Pods/Target Support Files/opencv_core/opencv_core.release.xcconfig
— replacing "DT_TOOLCHAIN_DIR" with "TOOLCHAIN_DIR".

I didn't meet this issue with XCode 16, there is nothing like toolchain is defined by this package, so it's more likely to be the issue of flutter or xcode, anyway, it can be solved, thanks for sharing the solution 😄

// opencv_core.release.xcconfig generated in my case

CLANG_WARN_QUOTED_INCLUDE_IN_FRAMEWORK_HEADER = NO
CODE_SIGN_IDENTITY =
CONFIGURATION_BUILD_DIR = ${PODS_CONFIGURATION_BUILD_DIR}/opencv_core
DEFINES_MODULE = YES
FRAMEWORK_SEARCH_PATHS = $(inherited) "${PODS_CONFIGURATION_BUILD_DIR}/DartCvMacOS"
GCC_PREPROCESSOR_DEFINITIONS = $(inherited) COCOAPODS=1
LIBRARY_SEARCH_PATHS = $(inherited) "${TOOLCHAIN_DIR}/usr/lib/swift/${PLATFORM_NAME}" /usr/lib/swift
OTHER_SWIFT_FLAGS = $(inherited) -D COCOAPODS
PODS_BUILD_DIR = ${BUILD_DIR}
PODS_CONFIGURATION_BUILD_DIR = ${PODS_BUILD_DIR}/$(CONFIGURATION)$(EFFECTIVE_PLATFORM_NAME)
PODS_DEVELOPMENT_LANGUAGE = ${DEVELOPMENT_LANGUAGE}
PODS_ROOT = ${SRCROOT}
PODS_TARGET_SRCROOT = ${PODS_ROOT}/../Flutter/ephemeral/.symlinks/plugins/opencv_core/macos
PODS_XCFRAMEWORKS_BUILD_DIR = $(PODS_CONFIGURATION_BUILD_DIR)/XCFrameworkIntermediates
PRODUCT_BUNDLE_IDENTIFIER = org.cocoapods.${PRODUCT_NAME:rfc1034identifier}
SKIP_INSTALL = YES
SWIFT_INCLUDE_PATHS = $(inherited) "${PODS_ROOT}/DartCvMacOS/libopencv"
USE_RECURSIVE_SCRIPT_INPUTS_IN_SCRIPT_PHASES = YES