Subframe


Subframe is a subtitle renderer that renders Subforge SubtitleDocument directly and targets libass visual parity for ASS/SSA on web and Bun. The core is CPU-rendered and deterministic; GPU backends only composite bitmaps.

Status

- Early but working. Visual parity is focused on the documented scope in docs/GOALS.md.
- WebGL and WebGPU backends are available; the CPU path remains the source of truth.

Features

- Deterministic, fixed-point (1/64 px) core rendering.
- libass-style raster + post filters (outline/blur/shadow).
- WebGL/WebGPU compositors with atlas-less uploads per layer (easy to extend later).
- Trace tooling for debug and parity analysis.

Playground

``
bun playground/index.html
`
Default backend selection order: WebGPU → WebGL → CPU.

Build

`
bun run build
`
Outputs ESM bundle to dist/.

Parity quickstart (smoke)

1) Build libass (submodule): tools/ref/build_libass.sh
2) Build the render helper (see tools/ref/README.md)
3) Run the smoke parity test:
`
bun run test:golden:smoke -- --trace-on-fail
`

Repository layout

`
src/ # Renderer core + backends
playground/ # Local demo UI
docs/ # Goals, architecture, perf notes
tools/ # Parity and diff tooling
test/ # Fixtures and golden data
refs/ # Reference submodules (libass, subforge, text-shaper)
`

Submodules

This repo uses reference submodules for implementation parity research:
`
git submodule update --init --recursive
`
See refs/README.md for details.

License

MIT. See LICENSE`.