Klappt is a small vocabulary learning app built with C++23, SDL3, SDL_ttf, Clay UI, Xapian, and LMDB. You add words to a learning list and review them with spaced repetition. Learning modes progress from recognizing the whole answer to filling gaps, rebuilding chunks, and composing the answer.

The base platforms are Android, iOS, and Web. Linux is used for development.

• Git submodules initialized:

  git submodule update --init --recursive

• Android Studio, Android SDK, and NDK for Android.
• Xcode and CMake for iOS.
• Emscripten SDK for Web.
• CMake 3.16+ and a C++23 compiler for Linux development.

The Android project lives under SDL's Android template. Copy this repository's Gradle file into the app module:

cp build.gradle SDL/android-project/app/build.gradle
cd SDL/android-project

Create SDL/android-project/local.properties so Gradle can find your SDK and NDK:

sdk.dir=/path/to/Android/Sdk
ndk.dir=/path/to/Android/Sdk/ndk/<version>

Build and install on a connected device or emulator:

./gradlew assembleDebug installDebug

The APK is produced under SDL/android-project/app/build/outputs/apk/.

To build, sign, and install the arm64-v8a release APK from the repository root:

./config/android-build-sign-install-arm64.sh

For Android Debug hot reload, keep the app running and run from the repository root:

./config/android-push-hotreload.sh --abi arm64-v8a

Generate the Xcode project from the repository root:

./config/config-ios-xcode.sh

Then open build/ios/klappt.xcodeproj in Xcode, select the klappt scheme, choose an iOS device or simulator, and build/run.

You can also build from the command line:

cmake --build build/ios --config Debug

source /path/to/emsdk/emsdk_env.sh
./config/config-web-unix.sh
cmake --build build/web
cd build/web
python3 -m http.server

Open http://localhost:8000/klappt.html in a browser.

cmake -S . -B build \
                  -DTRACY_ENABLED=OFF \
                  -DENABLE_HOTRELOAD=ON \
                  -DCMAKE_BUILD_TYPE=Debug \
                  -DSDL_X11_XCURSOR=OFF \
                  -DSDL_X11_XINPUT=OFF \
                  -DSDL_X11_XFIXES=OFF \
                  -DSDL_X11_XRANDR=OFF \
                  -DSDL_X11_XTEST=OFF
cmake --build build
./build/Debug/klappt

Debug builds support hot reload. To rebuild only the reloadable module:

cmake --build build --target app_hotreload

To enable Tracy profiling on native builds, configure with TRACY_ENABLED:

cmake -S . -B build-prof \                                                                                                           master ✚ ✱
                       -DTRACY_ENABLED=ON \
                       -DENABLE_HOTRELOAD=OFF \
                       -DCMAKE_BUILD_TYPE=Debug \
                       -DSDL_X11_XCURSOR=OFF \
                       -DSDL_X11_XINPUT=OFF \
                       -DSDL_X11_XFIXES=OFF \
                       -DSDL_X11_XRANDR=OFF \
                       -DSDL_X11_XTEST=OFF
cmake --build build-prof -j4 --target klappt
./build-prof/Debug/klappt

Then open the Tracy UI (tracy-profiler) and connect to the running app. TRACY_ENABLED is not supported for Web/Emscripten builds.