Sudoku Resolv

Photograph a sudoku puzzle, let OpenCV find the board and read the digits, then solve it. Originally a 2011 iOS 3.2 app; modernized in 2026 to iOS 16+, SwiftUI, and OpenCV 4.13.

Requirements

• Xcode 16 or newer
• opencv2.xcframework (OpenCV 4.13.0) at the repository root (see below)

Getting opencv2.xcframework

The xcframework is not checked in (it is ~37 MB of build output). Build it once from the official OpenCV 4.13.0 sources (needs cmake and python3):

git clone --depth 1 --branch 4.13.0 https://github.com/opencv/opencv.git
python3 opencv/platforms/apple/build_xcframework.py --out build \
    --iphoneos_archs arm64 --iphonesimulator_archs arm64 \
    --build_only_specified_archs \
    --without objc --without dnn --without gapi --without stitching \
    --without video --without videoio --without objdetect --without photo \
    --without calib3d --without features2d --without flann
cp -R build/opencv2.xcframework <this repo>/

(The official release asset opencv-4.13.0-ios-framework.zip is a fat framework without an arm64-simulator slice, so it cannot be used for simulator builds on Apple Silicon — hence the source build.)

Caching the built xcframework

Building takes 20+ minutes, so after a successful build we keep a tarball outside the repo. If opencv2.xcframework/ ever gets wiped (e.g. by git clean -fdx), restore it from the cache instead of rebuilding:

# save (run once, after building)
tar -czf ~/Library/Caches/opencv2.xcframework.tar.gz \
    -C <this repo> opencv2.xcframework

# restore
tar -xzf ~/Library/Caches/opencv2.xcframework.tar.gz \
    -C <this repo>

Note: git clean -fdx will remove the xcframework because it is gitignored. Use git clean -fdx -e opencv2.xcframework to preserve it.

Building and testing

xcodebuild -project Sudokubot.xcodeproj -scheme Sudokubot \
    -destination 'platform=iOS Simulator,name=iPhone 16' build

xcodebuild -project Sudokubot.xcodeproj -scheme Sudokubot \
    -destination 'platform=iOS Simulator,name=iPhone 16' test

Architecture

• SwiftUI app (SudokubotApp, HomeView, PreviewView, BoardView, ArchiveView, HelpView) with a Swift solver (Solver.swift) and archive layer (ArchiveEntry/ArchiveManager.swift — same on-disk format as the 2011 app).
• C++/Objective-C++ vision core on the OpenCV 4 C++ API: boardRecognizer (board detection + grid extraction), basicOCR (cv::ml::KNearest digit classifier), cvutil (UIImage <-> cv::Mat).
• SudokuBridge is the single thin Objective-C++ bridge Swift calls for board recognition.

App Store product page (original release): http://itunes.apple.com/us/app/sudoku-resolv/id446583583?ls=1&mt=8