text-typeset

Turns rich text documents into GPU-ready glyph quads.

Typesetting crate for the text-document ecosystem. Takes a rich text document model (styled paragraphs, tables, lists, frames) and produces positioned glyph quads, decoration rectangles, and a glyph atlas texture that any GPU framework can render in a few draw calls.

text-document (model) --> text-typeset (shaping + layout) --> framework adapter (rendering)

Architecture: shared service, owned flows

text-typeset is split along the axis of "what is shareable":

Type	Lifetime	Owns	Shared across
[TextFontService]	one per process / window	font registry, glyph atlas, glyph cache, swash scale context, HiDPI scale factor	every widget that emits text
[DocumentFlow]	one per widget	viewport, zoom, scroll, wrap mode, flow layout, cursor, colors, rendered frame	nothing — strictly per-widget

A DocumentFlow does not own font data. Every layout_* and render method takes a TextFontService reference and reads the font registry and glyph atlas through it. This makes it cheap to run many widgets against a single shared atlas — one GPU upload per frame, one shaped glyph rasterized at most once, and no cross-widget contamination of viewport / zoom / scroll state.

Put the service behind whatever smart pointer your host framework uses (an Rc<RefCell<TextFontService>> for single-threaded UIs, a plain &mut inside a render loop that already has exclusive access). Every widget owns its own DocumentFlow and calls flow.render(&mut *service.borrow_mut()) when it paints. Because the service carries no per-widget state, changes that widget A makes to set_viewport, set_zoom, set_scroll_offset, or set_cursor live on A's flow and never touch B's.

Features

• Text shaping via rustybuzz (Rust port of HarfBuzz) with OpenType feature support
• Font management via fontdb with CSS-spec font matching, generic family mapping, and glyph fallback
• Glyph rasterization via swash with color emoji support (COLR/CBDT)
• Glyph atlas backed by etagere shelf packing with auto-grow and LRU eviction — shared across every widget through the TextFontService
• Paragraph layout with line breaking (unicode-linebreak, UAX #14), four alignment modes (left, right, center, justify), and first-line indent
• BiDi text analysis via unicode-bidi with per-run directional shaping
• Tables with column width distribution, cell layout, borders, and cell backgrounds
• Lists with marker rendering (bullet, decimal, alpha, roman) at configurable indent levels
• Frames with inline, float-left, float-right, and absolute positioning
• Text decorations: underline, strikeout, overline (from font metrics)
• Letter spacing and word spacing
• Hit testing: screen coordinates to document position with region detection (text, margin, link, image)
• Cursor display with caret rendering, blink support, multi-cursor, and selection painting with full-width line highlighting
• Zoom: display zoom (0.1x to 10x) without text reflow, scales all output coordinates — owned per-widget
• Cell-level selection: table cell highlighting via selected_cells in cursor display
• Scrolling: ensure_caret_visible, scroll_to_position (automatic 1/3-viewport placement), viewport culling
• Incremental relayout: update a single block without re-laying-out the entire document
• Content width modes: auto (follows viewport) or fixed (for page-like WYSIWYG layout)
• HiDPI: the service carries a single scale factor and bumps a scale_generation counter on every change; each flow stamps the counter during layout and exposes layout_dirty_for_scale so the framework can detect and act on HiDPI transitions without tracking them itself

Framework-agnostic output

text-typeset produces a RenderFrame containing:

• Glyph quads ([screen_rect, atlas_rect, color]) drawn as textured rectangles from the atlas
• Image quads (position + resource name) for inline images loaded by the adapter
• Decoration rects (underline, strikeout, selection, cursor, table borders, backgrounds)
• Atlas texture (RGBA, updated incrementally)

The rendering contract is thin: "draw N sub-rects from a texture + M colored rects." Any framework that supports textured quads can serve as a backend: Godot (draw_texture_rect_region), Qt (QPainter::drawImage), wgpu, egui, iced.

Quick start — single widget

use text_typeset::{DocumentFlow, TextFontService};

// 1. Build the shared service once and register fonts on it.
let mut service = TextFontService::new();
let font = service.register_font(include_bytes!("test-fonts/NotoSans-Variable.ttf"));
service.set_default_font(font, 16.0);

// 2. Build a per-widget flow and give it a viewport.
let mut flow = DocumentFlow::new();
flow.set_viewport(800.0, 600.0);

// 3. Lay out + render. Every layout / render method takes the
//    service by reference so the glyph atlas stays shared.
let doc = text_document::TextDocument::new();
doc.set_plain_text("Hello, world!").unwrap();
flow.layout_full(&service, &doc.snapshot_flow());

let frame = flow.render(&mut service);
// frame.glyphs       -> glyph quads (textured rects from the shared atlas)
// frame.atlas_pixels -> RGBA texture to upload (or read via service.atlas_pixels())
// frame.decorations  -> cursor, selection, underlines, borders

Quick start — multiple widgets on one document

Two widgets — say, a live editor and a read-only preview — share a TextDocument, a TextFontService, and produce glyphs into the same atlas. Each owns its own DocumentFlow with its own viewport / zoom / scroll:

use std::cell::RefCell;
use std::rc::Rc;
use text_typeset::{DocumentFlow, TextFontService};

let service: Rc<RefCell<TextFontService>> = {
    let mut svc = TextFontService::new();
    let face = svc.register_font(include_bytes!("test-fonts/NotoSans-Variable.ttf"));
    svc.set_default_font(face, 16.0);
    Rc::new(RefCell::new(svc))
};

let mut editor_flow = DocumentFlow::new();
editor_flow.set_viewport(600.0, 400.0);

let mut preview_flow = DocumentFlow::new();
preview_flow.set_viewport(500.0, 400.0);
preview_flow.set_zoom(0.8); // zoom lives on the flow — only affects this widget

let doc = text_document::TextDocument::new();
doc.set_plain_text("Hello, world!").unwrap();

editor_flow.layout_full(&service.borrow(), &doc.snapshot_flow());
preview_flow.layout_full(&service.borrow(), &doc.snapshot_flow());

let _editor_frame = editor_flow.render(&mut service.borrow_mut());
let _preview_frame = preview_flow.render(&mut service.borrow_mut());

Neither render call mutates state that belongs to the other flow. The atlas, shaper cache, and font registry are shared; the viewport, scroll, zoom, cursor, and flow layout are not.

Content width

By default, text wraps at the viewport width (web/editor style). For page-like layout:

// Fixed width: text wraps at 600px regardless of viewport size
flow.set_content_width(600.0);

// Back to auto: text reflows when viewport resizes
flow.set_content_width_auto();

HiDPI

set_scale_factor lives on the service because it drives the physical ppem of every rasterized glyph — one atlas, one scale:

service.set_scale_factor(2.0); // clears the atlas + glyph cache, bumps scale_generation

// Every flow stamps the service's scale_generation at layout time.
// After a change, ask whether a flow is stale and relayout if so:
if editor_flow.layout_dirty_for_scale(&service.borrow()) {
    editor_flow.layout_full(&service.borrow(), &doc.snapshot_flow());
}

The service cannot reach into per-widget flows, so it cannot clear their layouts for you. The generation counter makes that invalidation observable; the caller decides what to do with it.

Dependencies

Crate	Version	Purpose
rustybuzz	0.20	OpenType shaping
swash	0.2	Font metrics and glyph rasterization
fontdb	0.23	Font discovery and CSS-spec matching
etagere	0.3	Glyph atlas allocation (shelf packing)
unicode-linebreak	0.1	Line break opportunities (UAX #14)
unicode-bidi	0.3	Bidirectional text (UAX #9)
text-document	--	Document model (optional, default feature)

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.