IDML Faithful Renderer

Pixel-faithful renderer for Adobe IDML documents, built in Rust.

See idea.md for the full technical specification and /root/.claude/plans/do-a-deep-research-humming-wigderson.md for the development strategy this repository implements.

Current pipeline

idml bytes
 └─► paged-parse              ZIP + designmap + spread + story + graphic
      └─► paged-scene         owned Document (palette, spreads, stories,
                              frame-for-story index)
           └─► paged-text     rustybuzz shape + Knuth-Plass compose +
                              aligned layout (Left / Right / Center / Justify)
                 └─► paged-compose  DisplayCommand { FillPath | StrokePath },
                                    glyph outlines (ttf-parser), unit-rect
                                    + glyph path interning
                       └─► paged-gpu   tiny-skia CPU rasterizer (feature:
                                       "cpu", default-on); Vello backend
                                       placeholder for Spike A
                             └─► RgbaImage
                                   └─► image PNG encode
                                   └─► paged-fidelity  ΔE2000 + SSIM diff
                                                       against a reference

The pipeline is exposed as two library functions:

use paged_renderer::{Document, pipeline, PipelineOptions};

let document = Document::open(&idml_bytes)?;
let opts = PipelineOptions::default();

// Display list only.
let built = pipeline::build(&document, &opts)?;

// Display list + rasterised image (cpu feature).
let (built, image) = pipeline::render(&document, &opts, 144.0, Color::WHITE)?;

Workspace layout

crates/
├── paged-parse/       ZIP + XML → typed AST (container, designmap,
│                     spread, story, graphic)
├── paged-scene/       Owned Document: parsed container, palette,
│                     spreads, stories, frame-for-story index
├── paged-text/        Shape (rustybuzz) + compose (Knuth-Plass) +
│                     layout (alignment, positioned glyphs)
├── paged-color/       ICC transforms placeholder (lcms2 non-wasm)
├── paged-compose/     Display list, path buffer, emit primitives
│                     (emit_rect, emit_stroke_rect, emit_paragraph),
│                     glyph outlining via ttf-parser
├── paged-gpu/         PathRasterizer trait + cpu backend (tiny-skia);
│                     Vello backend gated behind vello-backend feature
├── paged-renderer/    Top-level library (`pipeline::build`,
│                     `pipeline::render`) + `paged-inspect` CLI
├── paged-fidelity/    ΔE2000 + SSIM diff harness + `paged-diff` CLI
└── paged-sdk/        wasm-bindgen surface: `render_to_png`,
                      `parse_summary`

spikes/
├── vello-eval/             Spike A harness (GPU feature coverage)
├── composer-calibration/   Spike B harness (InDesign line-break parity)
└── wasm-size/              Spike C harness (compressed artefact size)

corpus/
└── seeds/           Golden IDMLs + reference PDFs (to be populated)

.github/workflows/   ci.yml + fidelity.yml

CLI tools

• paged-inspect <file.idml> — parse a container, walk spreads and stories, print a human-readable summary. Flags: --font <path>, --display-list, --render <out.png>, --dpi <n>, --column-width-pt <n>, --default-size <n>.
• paged-diff <reference.png> <candidate.png> — ΔE2000 + SSIM report against the §13.2 pass criteria (mean ΔE ≤ 1.0, p99 ΔE ≤ 2.5, SSIM ≥ 0.99). Exits 0 on pass, 1 on fail.

IDML features supported today

• Container: ZIP + mimetype validation + sub-resource access
• designmap.xml manifest: spreads, stories, master-spread refs
• Resources/Graphic.xml: <Color> + <Swatch> + one-level indirection; CMYK / RGB / Gray → linear RGB (naive, non-ICC)
• Spread_*.xml: <Page> + <TextFrame> + <Rectangle> + ItemTransform, GeometricBounds, FillColor, StrokeColor, StrokeWeight; nested-in-<Group> frames surfaced as skipped
• Story_*.xml: <ParagraphStyleRange> (+ Justification, FirstLineIndent, SpaceBefore, SpaceAfter) wrapping <CharacterStyleRange> (+ AppliedFont, FontStyle, PointSize, FillColor, Tracking) wrapping <Content> and <Br/>
• Paragraph alignment: Left / Right / Center / Justify (last-line-left)
• Per-run fill colour picker (cluster → Paint)
• FillPath + StrokePath commands; glyph + rect path sharing via interned PathBuffer

Verification

cargo fmt --all --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace
./spikes/wasm-size/measure.sh          # requires binaryen + brotli
cargo check --target wasm32-unknown-unknown -p paged-sdk

All green at the latest commit on the current branch.

What is not yet implemented

The idea.md spec calls for a multi-year effort (3–5 engineers + 1 typographer over 36–39 months). This repository is the scaffolding + first slice — substantial, but far short of a print-grade renderer. Material items remaining include:

• Spike A — Vello feature-coverage evaluation needs real execution. The harness is in place; running it requires a GPU or software Vulkan (lavapipe).
• Spike B — Paragraph Composer calibration against InDesign output. Needs an InDesign-exported reference corpus; the 95% line-break parity gate is unpaved.
• Spike C — WASM size measurement script needs binaryen + brotli installed to run. The 3.5 MB pass criterion is not yet verified.
• ICC colour management — naive CMYK/RGB → linear RGB today; paged-color wraps lcms2 natively but the pipeline doesn't use it.
• Effects — drop shadow, feather, glow, blend modes other than source-over are not implemented.
• Text — no justification of metric-kerning ratios, no hyphenation, no drop caps / nested styles / GREP styles / tables / footnotes / text-on-path / CJK composition (§8.5).
• Images, gradients, spot colours — <Oval>, <Polygon>, <GraphicLine>, gradients, placed images, <PageItem> trees inside groups.
• Master spreads — referenced from the manifest, ignored today.
• Font resolver — hosts pass bytes directly; the spec calls for an async AssetResolver interface.
• Multi-page output — the pipeline unions all pages into one canvas; per-page rasterisation is a natural extension.
• Fidelity corpus — the diff harness works; the 500-document corpus is empty.
• CI on real corpus — workflow exists but gates nothing until the corpus is populated.

See idea.md §17 for the full risk register and §16 for the phased roadmap. The plan document at /root/.claude/plans/do-a-deep-research-humming-wigderson.md captures the de-risking sequence that this repository implements through Phase 0 foundations.

Branch

All development lands on claude/read-idea-file-vHroZ per the session-branch requirement.