A standalone C++17 reference implementation of the Morphe sketch schema: data structures, JSON (de)serialization, and validation. Mirrors the Python implementation in ../morphe/ but does not depend on it.

The two implementations agree on the wire format documented in ../SPECIFICATION.md §13 and pinned by the conformance corpus under ../tests/conformance/.

cmake -S . -B build
cmake --build build
ctest --test-dir build --output-on-failure

Requires CMake 3.16+, a C++17 compiler (gcc 9+, clang 9+, MSVC 2019+).

add_subdirectory(path/to/morphe/cpp)
target_link_libraries(your_target PRIVATE morphe::morphe)

morphe is a header-only INTERFACE library at this stage; linking it brings in the include path for <morphe/...> headers and the vendored <nlohmann/json.hpp>.

• third_party/nlohmann/json.hpp — nlohmann/json v3.11.3 (MIT)
• third_party/doctest/doctest.h — doctest/doctest v2.4.11 (MIT, tests only)

Both are checked in as single headers so the project builds offline with no CMake FetchContent dance.

The reference implementation covers:

• All core types (Point2D, Vector2D, PointType, PointRef).
• All seven primitive types (Line, Arc, Circle, Point, Spline, Ellipse, EllipticalArc) modeled as a std::variant.
• All 19 ConstraintType values plus the CONSTRAINT_RULES table.
• SketchDocument with insertion-ordered primitives.
• JSON (de)serialization matching the Python encoder byte-for-byte on shared corpus fixtures.
• Schema validation with the same severity-tagged issue codes as the Python validator (e.g., LINE_ZERO_LENGTH, ARC_RADIUS_INCONSISTENT, CONST_TOO_FEW_REFS), and the same 1-micron default tolerance.

Out of scope (matches the Python core): a constraint solver, CAD adapters (FreeCAD / SolidWorks / Inventor / Fusion), or computational helpers (B-spline evaluation, ellipse parametric, etc.). These belong above the schema layer.

The shared corpus under ../tests/conformance/*.json is the wire-format contract. It is generated from the Python implementation (tests/conformance/generate_corpus.py) and consumed by both:

• Python: tests/test_conformance_corpus.py checks that save_sketch(load_sketch(f)) == f byte-for-byte.
• C++: tests/test_conformance.cpp loads each fixture, round-trips through morphe::to_json, and compares parsed JSON trees with float tolerance. The rounded_rect.json fixture is also rebuilt in C++ and semantically compared, pinning the exact wire format.

CI (.github/workflows/cpp.yml) runs both checks on Ubuntu (gcc-13, clang-18), macOS, and Windows.

The C++ decoder accepts both the omit-when-default form (the canonical wire format described in SPECIFICATION.md §13.1.1) and the verbose form with explicit defaults ("value": null, "inferred": false, "confidence": 1.0). Documents from older or third-party encoders that emit defaults explicitly therefore load correctly. Round-tripping through morphe::to_json normalizes them to the minimal form.