@wingleeio/pretext-core

The pretext text engine as a C++ JSI module for React Native. It ports @chenglou/pretext (the line breaker and layout kernel) and @wingleeio/pretext-native (font-table advance metrics) to native C++, exposed as synchronous JSI calls via Nitro Modules. One codebase drives iOS and Android.

Why: on Hermes the JS engine spent ~2 ms per text node segmenting and measuring advances. In C++ that drops to tens of microseconds — measuring a whole 8,000 -block account becomes cheaper than hydrating a height cache. This is what lets mugen delete its persistent height/paint caches, the boot warmer, and the wormhole scroll on device. See mugen/NATIVE-TEXT.md.

Single import, two backends

import … from '@wingleeio/pretext-core' exposes the exact @chenglou/pretext (+ /rich-inline) function surface plus pretext-native's font registration API. It dispatches to:

• native — the PretextCore Nitro HybridObject (C++ kernel), when installed;
• JS fallback — @chenglou/pretext + @wingleeio/pretext-native, byte-for -byte identical, on web and in tests.

So mugen's measure code keeps its call sites; only the import changes.

Conformance is the contract

The C++ kernel must produce byte-identical output to the TS engine running on pretext-native's polyfills (exactly what ships on Hermes today). pnpm test builds a host CLI (tools/fixture-runner) and drives both engines over the same ops — the full 18-language corpus, rich-inline, and every layout API — comparing each number with Object.is and each string with ===. This runs in CI (pretext-core-conformance). See PORTING.md for the porting rules that make this hold (UTF-16 everywhere, doubles not floats, -ffp-contract =off, the neutral engine profile, a hermetic segmenter instead of ICU).

Layout

• cpp/pretext/** — the platform-independent kernel (segmenter, sfnt parser, analysis, line-break, layout, rich-inline, bidi) + generated Unicode tables.
• cpp/{PretextCoreModule,PreparedTextObject,PreparedRichInlineObject}.cpp — Nitro HybridObject implementations wrapping the kernel.
• src/ — the JS wrapper (index.ts) + native locator (native.ts).
• nitrogen/generated/ — Nitro codegen output (regenerate with npx nitrogen).
• scripts/gen-unicode-tables.mjs, scripts/gen-bidi-data.mjs — table generators (run on Node so the Unicode data matches the TS \p{…} regexes).

Build

• JS: pnpm build (tsdown → dist/).
• Host kernel + conformance CLI: pnpm build:host (CMake; needs cmake).
• iOS/Android: consumed as a Nitro module — pod install / gradle sync in the host app picks up PretextCore.podspec / android/build.gradle.