pydwshape

Windows-only. A DWriteCore-native per-lookup OpenType shaping tracer for BabelMap's OpenType test framework — the DirectWrite analogue of its HarfBuzz/HarfRust engines.

It shapes entirely with Microsoft DWriteCore (app-local, version-pinned) and returns the babelsoft /api/opentype/shape result dict, including the per-lookup glyph-mutation trace. No system dwrite.dll / TextShaping.dll is loaded (no DLL-hijack surface), and no subprocess is spawned — the Rust engine runs in-process via this PyO3 abi3 extension.

Requires

• Windows 10 1809+ (x64)
• CPython 3.9+ (any 3.9+ interpreter; wheel tag cp39-abi3-win_amd64)

Importing on any other OS raises OSError.

Install

pip install pydwshape

Usage

from pydwshape import shape_with_dwrite

font = open("font.otf", "rb").read()
res = shape_with_dwrite(font, "ᠰᠠᠢᠬᠠᠨ")  # script omitted -> auto-detected
res = shape_with_dwrite(font, "ᠰᠠᠢᠬᠠᠨ", script="mong")  # explicit
# res = {upem, glyph_count, stages:[{m,glyphs,depth,effective}], final, messages, engine}

script may be omitted (auto/empty behave the same): the script number is auto-detected from the text using DWriteCore's own Unicode script data (Common/Inherited/combining marks inherit from context).

features is a {tag: bool} map (same convention as the HarfBuzz/harfrust engines): optional features toggle ({"smcp": True}, {"liga": False} …); script-required features (Mongolian/Arabic init/medi/fina/rclt …) are fixed by DWriteCore and cannot be disabled.

Constraints

• Single-threaded by design: the per-lookup trace comes from a process-local hook that is installed per call and restored afterwards (the GIL serialises calls from Python, so repeated calls are safe).
• The hook is signature-locked to the bundled DWriteCore build (2.1.1.2605) with automatic relocation by prologue scan for newer builds.

Provenance / licensing

• Our Rust/Python code: MIT (see the source repository).
• Bundled DWriteCore.dll is Microsoft software from the Windows App SDK (Microsoft.WindowsAppSDK.DWrite), redistributed under Microsoft's license terms for that component; the DLL is Microsoft-signed and unmodified.

Build (maintainers, Windows)

# stage the MS-signed DWriteCore.dll (from build/dwc_poc or the Windows App SDK NuGet)
Copy-Item build\dwc_poc\DWriteCore.dll python\pydwshape-wheel\python\pydwshape\DWriteCore.dll
cd python\pydwshape-wheel
python -m pip install maturin
python -m maturin build --release --interpreter <python> -o dist