Vello

An experimental GPU compute-centric 2D renderer

Vello is an experimental 2D graphics rendering engine written in Rust, with a focus on GPU compute. It can draw large 2D scenes with interactive or near-interactive performance, using wgpu for GPU access.

Quickstart to run an example program:

cargo run -p with_winit

It is used as the rendering backend for Xilem, a Rust GUI toolkit.

[!WARNING] Vello can currently be considered in an alpha state. In particular, we're still working on the following:
Implementing blur and filter effects.
Conflations artifacts.
GPU memory allocation strategy
Glyph caching

Motivation

Vello is meant to fill the same place in the graphics stack as other vector graphics renderers like Skia, Cairo, and its predecessor project Piet. On a basic level, that means it provides tools to render shapes, images, gradients, text, etc, using a PostScript-inspired API, the same that powers SVG files and the browser <canvas> element.

Vello's selling point is that it gets better performance than other renderers by better leveraging the GPU. In traditional PostScript-style renderers, some steps of the render process like sorting and clipping either need to be handled in the CPU or done through the use of intermediary textures. Vello avoids this by using prefix-sum algorithms to parallelize work that usually needs to happen in sequence, so that work can be offloaded to the GPU with minimal use of temporary buffers.

This means that Vello needs a GPU with support for compute shaders to run.

Getting started

Vello is meant to be integrated deep in UI render stacks. While drawing in a Vello scene is easy, actually rendering that scene to a surface requires setting up a wgpu context, which is a non-trivial task.

To use Vello as the renderer for your PDF reader / GUI toolkit / etc, your code will have to look roughly like this:

// Initialize wgpu and get handles
let (width, height) = ...;
let device: wgpu::Device = ...;
let queue: wgpu::Queue = ...;
let surface: wgpu::Surface<'_> = ...;
let texture_format: wgpu::TextureFormat = ...;
let mut renderer = Renderer::new(
   &device,
   RendererOptions {
      surface_format: Some(texture_format),
      use_cpu: false,
      antialiasing_support: vello::AaSupport::all(),
      num_init_threads: NonZeroUsize::new(1),
   },
).expect("Failed to create renderer");

// Create scene and draw stuff in it
let mut scene = vello::Scene::new();
scene.fill(
   vello::peniko::Fill::NonZero,
   vello::Affine::IDENTITY,
   vello::Color::rgb8(242, 140, 168),
   None,
   &vello::Circle::new((420.0, 200.0), 120.0),
);

// Draw more stuff
scene.push_layer(...);
scene.fill(...);
scene.stroke(...);
scene.pop_layer(...);

// Render to your window/buffer/etc.
let surface_texture = surface.get_current_texture()
   .expect("failed to get surface texture");
renderer
   .render_to_surface(
      &device,
      &queue,
      &scene,
      &surface_texture,
      &vello::RenderParams {
         base_color: Color::BLACK, // Background color
         width,
         height,
         antialiasing_method: AaConfig::Msaa16,
      },
   )
   .expect("Failed to render to surface");
surface_texture.present();

See the examples/ folder to see how that code integrates with frameworks like winit and bevy.

Performance

We've observed 177 fps for the paris-30k test scene on an M1 Max, at a resolution of 1600 pixels square, which is excellent performance and represents something of a best case for the engine.

More formal benchmarks are on their way.

Integrations

SVG

A separate Linebender integration for rendering SVG files is available through the vello_svg crate.

Lottie

A separate Linebender integration for playing Lottie animations is available through the velato crate.

Examples

Our examples are provided in separate packages in the examples folder. This allows them to have independent dependencies and faster builds. Examples must be selected using the --package (or -p) Cargo flag.

Winit

Our winit example (examples/with_winit) demonstrates rendering to a winit window. By default, this renders the GhostScript Tiger as well as all SVG files you add in the examples/assets/downloads/ directory. A custom list of SVG file paths (and directories to render all SVG files from) can be provided as arguments instead. It also includes a collection of test scenes showing the capabilities of vello, which can be shown with --test-scenes.

cargo run -p with_winit

Some default test scenes can be downloaded from Wikimedia Commons using the download subcommand. This also supports downloading from user-provided URLS.

cargo run -p with_winit -- download

Bevy

The Bevy example (examples/with_bevy) demonstrates using Vello within a Bevy application. This currently draws to a wgpu Texture using vello, then uses that texture as the faces of a cube.

cargo run -p with_bevy

There is also a separate community integration for rendering raw scenes or Lottie and SVG files through bevy_vello.

Platforms

We aim to target all environments which can support WebGPU with the default limits. We defer to wgpu for this support. Other platforms are more tricky, and may require special building/running procedures.

Web

Because Vello relies heavily on compute shaders, we rely on the emerging WebGPU standard to run on the web. Until browser support becomes widespread, it will probably be necessary to use development browser versions (e.g. Chrome Canary) and explicitly enable WebGPU.

The following command builds and runs a web version of the winit demo. This uses cargo-run-wasm to build the example for web, and host a local server for it

# Make sure the Rust toolchain supports the wasm32 target
rustup target add wasm32-unknown-unknown

# The binary name must also be explicitly provided as it differs from the package name
cargo run_wasm -p with_winit --bin with_winit_bin

There is also a web demo available here on supporting web browsers.

[!WARNING] The web is not currently a primary target for Vello, and WebGPU implementations are incomplete, so you might run into issues running this example.

Android

The with_winit example supports running on Android, using cargo apk.

cargo apk run -p with_winit

[!TIP] cargo apk doesn't support running in release mode without configuration. See their crates page docs (around package.metadata.android.signing.<profile>).
See also cargo-apk#16. To run in release mode, you must add the following to examples/with_winit/Cargo.toml (changing $HOME to your home directory):

[package.metadata.android.signing.release]
path = "$HOME/.android/debug.keystore"
keystore_password = "android"

[!NOTE] As cargo apk does not allow passing command line arguments or environment variables to the app when ran, these can be embedded into the program at compile time (currently for Android only) with_winit currently supports the environment variables:
VELLO_STATIC_LOG, which is equivalent to RUST_LOG
VELLO_STATIC_ARGS, which is equivalent to passing in command line arguments

For example (with unix shell environment variable syntax):

VELLO_STATIC_LOG="vello=trace" VELLO_STATIC_ARGS="--test-scenes" cargo apk run -p with_winit --lib

Minimum supported Rust Version (MSRV)

This version of Vello has been verified to compile with Rust 1.75 and later.

Future versions of Vello might increase the Rust version requirement. It will not be treated as a breaking change and as such can even happen with small patch releases.

As time has passed, some of Vello‘s dependencies could have released versions with a higher Rust requirement. If you encounter a compilation issue due to a dependency and don’t want to upgrade your Rust toolchain, then you could downgrade the dependency.

# Use the problematic dependency's name and version
cargo update -p package_name --precise 0.1.1

Community

Discussion of Vello development happens in the Linebender Zulip, specifically the #gpu stream. All public content can be read without logging in.

Contributions are welcome by pull request. The Rust code of conduct applies.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be licensed as noted in the “License” section, without any additional terms or conditions.

History

Vello was previously known as piet-gpu. This prior incarnation used a custom cross-API hardware abstraction layer, called piet-gpu-hal, instead of wgpu.

An archive of this version can be found in the branches custom-hal-archive-with-shaders and custom-hal-archive. This succeeded the previous prototype, piet-metal, and included work adapted from piet-dx12.

The decision to lay down piet-gpu-hal in favor of WebGPU is discussed in detail in the blog post Requiem for piet-gpu-hal.

A vision document dated December 2020 explained the longer-term goals of the project, and how we might get there. Many of these items are out-of-date or completed, but it still may provide some useful background.

Related projects

Vello takes inspiration from many other rendering projects, including:

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

In addition, all files in the shader and src/cpu_shader directories and subdirectories thereof are alternatively licensed under the Unlicense (shader/UNLICENSE or http://unlicense.org/). For clarity, these files are also licensed under either of the above licenses. The intent is for this research to be used in as broad a context as possible.

The files in subdirectories of the examples/assets directory are licensed solely under their respective licenses, available in the LICENSE file in their directories.