Render GPU-accelerated 2D vector graphics (bezier paths, fills, strokes,
gradients) and high-quality shaped text in Rust with the Linebender stack:
Vello (compute-based vector renderer on wgpu) + Parley (text shaping/layout)
+ kurbo (geometry) + peniko (brushes/color). Covers winit+wgpu surface setup,
building a Scene every frame, feeding Parley glyph runs into Vello, the
retained-vs-immediate question, vsync/frame pacing, and the version-pinning
minefield between vello/wgpu/parley. Activate on: "Vello", "Parley",
"Linebender", "GPU vector rendering in Rust", "render text with wgpu",
"kurbo bezier", "peniko brush", "draw_glyphs", "Scene::fill", "custom 2D GPU
canvas". NOT for: 3D rendering (use wgpu directly or bevy), Metal shader
authoring (use metal-text-pipeline / metal-shader-expert), web canvas
(use Canvas2D/WebGL), or native OS widgets (use gpui/egui/iced).
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license
Apache-2.0
name
vello-parley-rendering
description
Render GPU-accelerated 2D vector graphics (bezier paths, fills, strokes,
gradients) and high-quality shaped text in Rust with the Linebender stack:
Vello (compute-based vector renderer on wgpu) + Parley (text shaping/layout)
+ kurbo (geometry) + peniko (brushes/color). Covers winit+wgpu surface setup,
building a Scene every frame, feeding Parley glyph runs into Vello, the
retained-vs-immediate question, vsync/frame pacing, and the version-pinning
minefield between vello/wgpu/parley. Activate on: "Vello", "Parley",
"Linebender", "GPU vector rendering in Rust", "render text with wgpu",
"kurbo bezier", "peniko brush", "draw_glyphs", "Scene::fill", "custom 2D GPU
canvas". NOT for: 3D rendering (use wgpu directly or bevy), Metal shader
authoring (use metal-text-pipeline / metal-shader-expert), web canvas
(use Canvas2D/WebGL), or native OS widgets (use gpui/egui/iced).
allowed-tools
Read,Write,Edit,Bash,Glob,Grep,WebSearch,WebFetch
metadata
{"category":"Frontend & UI","tags":["vello","parley","wgpu","rust","gpu","vector-graphics","text-rendering","linebender","kurbo","peniko"],"pairs-with":[{"skill":"metal-text-pipeline","reason":"The bare-metal counterpart — what Vello hides, and when pure Metal is worth it."},{"skill":"metal-shader-expert","reason":"For when you drop below Vello into MSL compute/fragment shaders."},{"skill":"rust-app-distribution","reason":"Shipping the signed/notarized desktop binary that hosts the renderer."}],"provenance":{"kind":"first-party","owners":["port-daddy"]},"authorship":{"maintainers":["port-daddy"]}}
Vello + Parley GPU Vector Rendering (Rust)
Vello is a compute-shader 2D vector renderer: you hand it a Scene (a list
of filled/stroked paths, images, glyph runs) and it rasterizes the whole thing
on the GPU in a few compute passes. Parley is the text half: it shapes and
lays out Unicode runs (via HarfRust + Swash/Skrifa) and yields positioned
glyphs you stream straight into the same Vello Scene. Together they give you a
pixel-perfect, fully custom 2D canvas with no widget model in the way —
which is the entire reason you'd reach for them over gpui/egui.
This skill is the worked, version-pinned, gotcha-annotated path from "blank
window" to "anti-aliased beziers + crisp shaped text at 120fps." The worked
example is real: core/pd-timeline-proto/ in this repo renders a scrubable
timeline (tracks, event markers, causal bezier threads, a playhead) this way.
When To Use
You need a bespoke 2D visualization (timeline, node graph, waveform, map,
diagram) where every pixel is yours and a retained widget tree gets in the way.
You want resolution-independent vector output (smooth zoom, crisp on HiDPI)
without managing your own tessellation/rasterization.
You need high-quality text (real shaping, ligatures, variable fonts, RTL)
rather than a bitmap-font hack.
You're already on wgpu and want a 2D layer that composes with your 3D, or you
want one renderer that runs on Metal/Vulkan/DX12/GL from one codebase.
NOT For
3D scenes, meshes, lighting → use wgpu directly, or bevy.
Authoring the shaders themselves → metal-shader-expert (MSL) or wgpu WGSL.
The "should I even leave gpui?" decision and pure-Metal costs →
metal-text-pipeline.
Native OS controls, accessibility trees, text input widgets → gpui, egui,
iced. Vello draws; it does not give you a button or a focus ring.
Web targets → Canvas2D / WebGL / WebGPU bindings, not native Vello (Vello does
have a web path, but if web is your primary target start there).
Decision Points
1. Pick the stack layer you actually need
What are you drawing?
├─ Arbitrary 2D vector + text, custom layout
│ └─ Vello (Scene) + Parley (text) + kurbo (geom) + peniko (brush) ← this skill
├─ 2D but you want widgets/layout/events handed to you
│ └─ Xilem (Linebender's UI framework, built on Vello+Parley) or egui/iced
├─ Just static SVG → raster once
│ └─ resvg / usvg (CPU) is simpler; skip the GPU entirely
└─ 3D / GPGPU
└─ wgpu directly; Vello is the wrong tool
2. Windowing + GPU surface
Need a window?
├─ Cross-platform desktop → winit 0.30 (ApplicationHandler model)
│ └─ GPU via wgpu; Vello ships `vello::util::RenderContext` to manage
│ Instance/Adapter/Device/Surface for you — USE IT, don't hand-roll wgpu init
├─ Embedding in an existing wgpu app
│ └─ Construct `Renderer` against your existing Device; render to your texture
└─ Headless render-to-PNG (tests, thumbnails, CI)
└─ Vello can render to a wgpu texture you read back; no surface needed
3. Retained vs immediate (Vello's real model)
Vello is immediate from your side, retained on the GPU side. You rebuild a
Scene each frame with scene.reset() then re-fill/stroke/draw_glyphs.
This sounds wasteful; it isn't — scene encoding is CPU-cheap (microseconds for
thousands of primitives) and the GPU does the heavy raster.
Rebuilding the scene every frame is the NORMAL pattern.
├─ Static content, rare changes → still rebuild; it's fine. Don't over-engineer caching.
├─ Huge scenes (100k+ paths) → consider sub-scenes / append() of cached fragments
└─ NEVER try to "diff" or mutate a Scene in place — that's not the API.
4. Anti-aliasing config
RendererOptions.antialiasing_support + RenderParams.antialiasing_method must AGREE.
├─ Cheapest, great for UI/vector → AaSupport::area_only() + AaConfig::Area
├─ MSAA8/MSAA16 → heavier, only if Area shows artifacts on thin strokes
└─ Mismatch (support says Area, params ask Msaa16) → panic at render time.
5. Frame pacing
PresentMode?
├─ AutoVsync (default, recommended) → tear-free, caps to display (60/120 ProMotion)
├─ AutoNoVsync → uncapped; use ONLY to benchmark raw GPU headroom, not to ship
└─ On ProMotion you get 120fps free IF you request a redraw every frame.
winit only redraws on request — call window.request_redraw() to keep animating.
Failure Modes
1. Version skew between vello / wgpu / parley (the #1 time sink)
Symptoms: expected wgpu::Device, found wgpu::Device (two wgpu majors in
the tree); RenderSurface field/method not found; trait bound errors on
Brush.
Root cause: vello re-exports a specific wgpu major. If your Cargo.toml
pulls a different wgpu, you have two incompatible wgpu crates.
Fix: Let vello own the wgpu version. Either depend on vello only and use
vello::wgpu::…, or pin your direct wgpu to exactly the major vello uses
(vello 0.3 → wgpu 22; check cargo tree -i wgpu). Same discipline for parley:
vello 0.3 pairs with parley 0.2 / peniko 0.2 / kurbo 0.11.
Detect: cargo tree -d (the -d finds duplicate crates). Two wgpu
entries = you will fail to compile or get cryptic type errors.
2. Glyph normalized-coords type mismatch
Symptoms: expected &[F2Dot14], found &[i16] when calling
.normalized_coords(...) on draw_glyphs.
Root cause: Parley yields variation coords as &[i16]; Vello/Skrifa wants
&[NormalizedCoord] (a #[repr(transparent)] wrapper over the same i16 bits,
F2Dot14).
Fix: reinterpret the slice — they are layout-identical:
let coords: &[skrifa::raw::types::F2Dot14] = unsafe { std::slice::from_raw_parts(raw.as_ptr().cast(), raw.len()) };
(Both are 2-byte; this is the idiom the parley examples use.)
Fix: pin exact minors and read THAT version's examples/ (clone the tagged
repo or open docs.rs at the pinned version). Don't trust a blog post for a
different minor. peniko::Color::with_alpha_factor → multiply_alpha;
Layout::align(width, alignment) dropped its trailing bool.
4. Borrow-checker fights in the winit ApplicationHandler
Symptoms: "cannot borrow *self as immutable because it is also borrowed
as mutable" inside window_event.
Root cause: holding let state = self.state.as_mut() across calls to other
&self/&mut self helpers and disjoint fields.
Fix: pull the Arc<Window> + dims out up front into locals, drop the
state binding, then take short, scoped borrows. Access disjoint struct
fields directly (e.g. &self.context, self.renderers[i], &self.scene) so
the borrow checker can split the &mut self — don't funnel them through one
intermediate &mut state.
5. Black / empty window
Symptoms: window opens, renders nothing.
Checklist: (a) did you request_redraw() after resume/resize? winit won't
redraw on its own. (b) RenderParams.width/height must match the surface
config, not the logical size. (c) surface format from
surface.config.format must be what the Renderer was created with. (d) you
called surface_texture.present(). (e) scene.reset() then actually pushed
primitives.
6. HiDPI text/geometry at half/double size
Root cause: mixing logical and physical pixels. winit gives physical
surface sizes; your layout is usually in logical points.
Fix: pass window.scale_factor() into Parley's layout (ranged_builder
takes a scale) AND into your geometry transform, consistently. Decide one
coordinate space and convert at the boundary.
Worked Example
A minimal-but-complete loop (the shape core/pd-timeline-proto uses). Pinned to
vello 0.3 / wgpu 22 / parley 0.2 / peniko 0.2 / kurbo 0.11 / winit 0.30.
// Cargo.toml: vello="0.3" wgpu="22" winit="0.30" parley="0.2"// peniko="0.2" kurbo="0.11" pollster="0.4"use vello::util::{RenderContext, RenderSurface};
use vello::{AaConfig, AaSupport, Renderer, RendererOptions, RenderParams, Scene};
use vello::peniko::{Color, Fill};
use vello::wgpu; // <- use vello's re-exported wgpu, never a second oneuse kurbo::{Affine, Circle, Point, Stroke, Line};
// 1. Surface (winit Window -> wgpu Surface), let Vello's RenderContext drive wgpu init.letmut cx = RenderContext::new();
letsurface: RenderSurface =
pollster::block_on(cx.create_surface(window.clone(), w, h, wgpu::PresentMode::AutoVsync))?;
// 2. One Renderer per device. AA support must match the AA you ask for at render time.letmut renderer = Renderer::new(
&cx.devices[surface.dev_id].device,
RendererOptions {
surface_format: Some(surface.format),
use_cpu: false,
antialiasing_support: AaSupport::area_only(), // pairs with AaConfig::Area below
num_init_threads: None,
},
)?;
// 3. Per frame: rebuild the scene from scratch.letmut scene = Scene::new();
scene.reset();
scene.stroke(&Stroke::new(1.0), Affine::IDENTITY, Color::rgb8(0x2a,0x32,0x3c), None,
&Line::new(Point::new(0.0, 100.0), Point::new(800.0, 100.0)));
scene.fill(Fill::NonZero, Affine::IDENTITY, Color::rgb8(0x4f,0xd1,0x6b), None,
&Circle::new(Point::new(120.0, 100.0), 5.0));
// (text via Parley -> scene.draw_glyphs(...); see references/parley-glyph-runs.md)// 4. Render to the surface.lettex = surface.surface.get_current_texture()?;
letdev = &cx.devices[surface.dev_id];
renderer.render_to_surface(&dev.device, &dev.queue, &scene, &tex, &RenderParams {
base_color: Color::rgb8(0x0d,0x11,0x17),
width: w, height: h,
antialiasing_method: AaConfig::Area, // must agree with AaSupport above
})?;
tex.present();
window.request_redraw(); // keep animating; winit won't redraw on its own
Text (the Parley half), the part everyone gets stuck on: build a Layout,
break_all_lines, align, then for each PositionedLayoutItem::GlyphRun, call
scene.draw_glyphs(font).brush(..).transform(..).font_size(..).normalized_coords(coords).draw(Fill::NonZero, glyphs)
where glyphs is an iterator of vello::Glyph { id, x, y } you accumulate by
advancing x += g.advance. See references/parley-glyph-runs.md for the exact,
compile-checked function.
Anti-Patterns
Anti-Pattern 1: Pulling your own wgpu next to Vello's
# ❌ two wgpu majors in the tree -> type mismatches everywherevello = "0.3"wgpu = "0.20"# vello 0.3 wants wgpu 22
# ✅ either use vello::wgpu, or pin the SAME major vello usesvello = "0.3"wgpu = "22"# matches; verify with `cargo tree -d`
Anti-Pattern 2: Caching/diffing the Scene to "save work"
Rebuilding the scene each frame is the intended model and costs microseconds.
Building a retained scene-graph diff layer on top is wasted complexity and fights
the API. Only reach for Scene::append of cached sub-scenes when you have
genuinely huge (100k+ primitive) static regions, measured.
Anti-Pattern 3: Bitmap fonts / texture-atlas-by-hand for text
Vello + Parley already do GPU glyph rendering with real shaping. Hand-rolling a
bitmap atlas throws away ligatures, hinting, variable fonts, RTL/complex scripts,
and HiDPI crispness. If you think you need a manual atlas, you're below the right
layer — see metal-text-pipeline for when that's actually justified.
Anti-Pattern 4: Ignoring request_redraw and wondering why it's static
winit is event-driven. No redraw request → no frame. Animations, scrubbing, and
auto-play all require you to request the next redraw (from resumed, after input,
and at the end of a frame while animating).
Anti-Pattern 5: Trusting a tutorial for a different crate version
These crates are pre-1.0 and rename things between minors. A snippet for vello
0.2 will not compile against 0.3. Always read the examples/ in the tagged
release matching your pin.
References
references/version-matrix.md — known-good vello/wgpu/parley/peniko/kurbo/winit
version combinations and how to verify with cargo tree -d.
references/parley-glyph-runs.md — the exact, compile-checked
render_glyph_run function that feeds Parley output into a Vello Scene,
including the i16 -> F2Dot14 coords reinterpret.
Provenance
Worked example and gotchas verified against core/pd-timeline-proto/ in this
repo (a winit+wgpu+Vello+Parley "Voyage Timeline" window), built and run on
Apple M4 Max (Metal backend) at sub-millisecond per-frame GPU cost.
Skill Bundle Index
Every file in this skill, and when to open it. Auto-generated; run scripts/index_references.py --fix.
references/
references/parley-glyph-runs.md — Feeding Parley glyph runs into a Vello Scene — The single function everyone gets stuck writing.
references/version-matrix.md — Vello / wgpu / Parley version matrix — Pre-1.0 Linebender crates move in lockstep clusters.
