OpenCV 5 Support

[curtis18]

Will gocv support OpenCV 5 https://opencv.org/opencv-5/? Thank you.

[swdee]

I "vibed" what the changes may look like to support v5 as its not a simple matter of changing the version number as a 4.x release is. I have a few days coming up so will take a proper look.

1. C++17 required
   GoCV’s C++ wrapper build flags need to use C++17 for OpenCV 5. OpenCV 5 requires C++17 minimum.

2. Removed legacy C API
   GoCV mostly wraps OpenCV C++ with its own C ABI, so this is likely okay unless any wrapper still uses old CvMat, IplImage, etc. OpenCV 5 removed those fully.

3. Module/header changes
   Some GoCV wrapper files will need include/link changes:

• features2d became features; function/class names mostly unchanged.
• calib3d split into geometry, calib, stereo, ptcloud, but old opencv2/calib3d.hpp still includes the new headers, so this may keep compiling.
• some imgproc geometry functions moved to geometry, so wrappers around convexHull, minAreaRect, fitEllipse, etc. may need opencv2/geometry.hpp.

4. Objdetect breakage likely
   GoCV currently exposes CascadeClassifier and HOGDescriptor; OpenCV 5 moved Haar cascade and HOG to opencv_contrib/xobjdetect.
   So GoCV either needs:

• build OpenCV 5 with contrib and update headers, or
• make those bindings conditional / removed for non-contrib builds.

5. DNN breakage
   GoCV exposes ReadNetFromCaffe; OpenCV 5 removed Caffe and Darknet parsers, recommending ONNX instead.
   ReadNetFromONNX should remain the safe path.

6. Behavior/test changes
   Some tests may fail due to changed behavior, not compile errors:

• VideoCapture.Get() returns -1 for unsupported props instead of 0.
• text rendering output changes.
• resize/warp numerical output may differ.

[swdee]

I have ported the code to work with v5 here - there are a number of breaking changes so we would need to implement versioning with Go Modules to maintain a v4 and v5 branches.

I am currently cleaning up and getting the build/CI stuff working, but this is a slow process. Once that is complete I will open a PR here to discuss and review whats been done.

[swdee]

PR #1371 now opened