CascadeClassifier fails to load from file with "Failed to lookup symbol 'cv_CascadeClassifier_create'"

[nombrekeff]

Describe the bug
I'm trying the CascadeClassifier, I'm trying to load the haar from a file downloaded from opencv repo: https://github.com/opencv/opencv/blob/4.x/data/haarcascades/haarcascade_frontalface_default.xml

To Reproduce
Steps to reproduce the behavior:

Call CascadeClassifier.empty or CascadeClassifier.fromFile:

var haar = CascadeClassifier.empty();

// Or 
var file = await getAssetFile('assets/haarcascade_frontalface_default.xml', 'haarcascade_frontalface_default.xml');
var haar = CascadeClassifier.fromFile(file.path);

Gives an error:

Unhandled Exception: Invalid argument(s): Failed to lookup symbol 'cv_CascadeClassifier_create': undefined symbol: cv_CascadeClassifier_create

Expected behavior
I would expect this to work. If the interface is in place I would assume it works.

Additional context
Add any other context about the problem here.

[rainyl]

@nombrekeff Hi.

I need more information to locate the problem, please also describe below questions:

1. which version of opencv_dart or opencv_core do you use? Do you use dartcv directly?
2. what's your flutter version?
3. which platform do you use? android, macos, ios, linux or windows?

[nombrekeff]

Hi thanks for the quick reply!

Sorry, my bad, thought i added versions!

I'm using:

• opencv_core: 1.4.1
• flutter: 3.33.0 - using master channel, might be an issue?
  • Specifically: 3.33.0-1.0.pre.426
• dart: 3.9.0
• I'm trying on android, with physical device

I can provide sample code if needed, but I'm not doing much. Just trying to instantiate the CascadeClassifier.

[nombrekeff]

@rainyl Sorry, I just figured out I modified the build only to compile IMPROC and core, and not object detect module.

[nombrekeff]

@rainyl Just to know, as I need the compiled opencv .so file to be as small as possible. What modules are required for the classifier to work? I tried with only IMPROC and OBJDETECT, but did not work, had to enable all modules again to get it to work, so don't know which modules are required.

[rainyl]

core is always need since some common structures are defined, also some internal dependencies exist but I have forgot. I remember that conan has a script, you can find some clues in it, here is the link: https://github.com/conan-io/conan-center-index/blob/b6a7593895a1cbab3c95afe1192fc978838694b3/recipes/opencv/4.x/conanfile.py

[rainyl]

I find it, objdetect requires core, calib3d and imgproc, https://github.com/conan-io/conan-center-index/blob/b6a7593895a1cbab3c95afe1192fc978838694b3/recipes/opencv/4.x/conanfile.py#L568-L572

[rainyl]

Oh, wait, I just forgot that we have primarily supported it in another way for win, linux and android in #355.

You can refer to https://github.com/rainyl/opencv_dart/tree/main/packages/opencv_dart#example-pubspecyaml-configuration for a configuration example.

This feature is not officially published to pub.dev, so you need to add the dependency of opencv_core or opencv_dart via github

dependencies:
  opencv_core:
    git:
      url: https://github.com/rainyl/opencv_dart.git
      path: packages/opencv_core
      ref: 271bb3f

Feel free to report here if it doesn't work for you.

[nombrekeff]

That's amazing, thanks! I will try it and let you know if I find any issues!

[nombrekeff]

Are there plans to support this for iOS?

Oh, wait, I just forgot that we have primarily supported it in another way for win, linux and android in #355.

You can refer to https://github.com/rainyl/opencv_dart/tree/main/packages/opencv_dart#example-pubspecyaml-configuration for a configuration example.

This feature is not officially published to pub.dev, so you need to add the dependency of opencv_core or opencv_dart via github

[rainyl]

Are there plans to support this for iOS?

Sadly no. Since flutter doesn't use cmake on macos and ios, also we didn't find a way to get user project directory in cocoapods script.

However, like I said in your another issue, with Native-Assets equipped, all platform including macos and ios will be supported.