vello_hybrid: Remove handling of `undefined` from gradient LUT (#1529) Closes #1528. # Context Nearly all gradients have a clearly defined value at all position, the only exception being very specific degenerate radial gradients. The behavior in this case is that all positions that are undefined should yield a transparent pixel. Previously, we had handling for this in the CPU shader, where at sampling time we would explicitly mask out such positions. As part of https://github.com/linebender/vello/pull/1301, a number of performance changes were introduced for gradient handling. Among that, a trick was used that encodes an additional transparent padding pixel in the gradient LUT, allowing to handle that case much better in Vello CPU. While this is a valid approach, it has two problems: 1) It destroys the assumption that the length of gradient LUTs are a multiple of 2. While for Vello CPU this doesn't matter and it currently also doesn't matter for Vello Hybrid, it could be a very useful property to have in the future, especially if we decide to change how gradients are uploaded in Vello hybrid. 2) It requires us to cache stops based on whether the underlying gradient has potentially undefined locations, which is also unfortunate and the root cause for #1528. # Solution This PR revert that change (while still keeping in-tact the other performance changes from that PR), such that gradients LUT's are always a multiple of 2 again and don't need to know anything about undefined locations. From my benchmarks, this doesn't have any notable performance impact for the normal case. In certain cases, it seems to even slightly improve performance. While I haven't measured it, this is likely to make undefined gradients about 2x slower, but since those are very rare edge cases we don't really care about apart from for correctness, I think this is very much a worthy change. Here you can find the change in performance before vs. after this PR: ``` fine/gradient/linear/opaque_u8_neon time: [359.08 ns 360.57 ns 362.26 ns] change: [-5.0401% -4.6310% -4.2254%] (p = 0.00 < 0.05) Performance has improved. Found 9 outliers among 100 measurements (9.00%) 1 (1.00%) low severe 3 (3.00%) high mild 5 (5.00%) high severe fine/gradient/radial/opaque_u8_neon time: [475.66 ns 476.60 ns 477.56 ns] change: [-1.3570% -1.0840% -0.8030%] (p = 0.00 < 0.05) Change within noise threshold. Found 7 outliers among 100 measurements (7.00%) 4 (4.00%) low mild 2 (2.00%) high mild 1 (1.00%) high severe fine/gradient/radial/opaque_conical_u8_neon time: [577.07 ns 578.02 ns 579.05 ns] change: [-1.2222% -0.8150% -0.3570%] (p = 0.00 < 0.05) Change within noise threshold. Found 12 outliers among 100 measurements (12.00%) 1 (1.00%) low mild 5 (5.00%) high mild 6 (6.00%) high severe fine/gradient/sweep/opaque_u8_neon time: [847.68 ns 849.27 ns 850.89 ns] change: [-0.0226% +0.2834% +0.5911%] (p = 0.07 > 0.05) No change in performance detected. Found 2 outliers among 100 measurements (2.00%) 1 (1.00%) low mild 1 (1.00%) high severe fine/gradient/extend/pad_u8_neon time: [346.25 ns 346.96 ns 347.77 ns] change: [-0.2873% +0.0627% +0.3827%] (p = 0.72 > 0.05) No change in performance detected. Found 5 outliers among 100 measurements (5.00%) 1 (1.00%) low mild 3 (3.00%) high mild 1 (1.00%) high severe fine/gradient/extend/repeat_u8_neon time: [368.20 ns 369.45 ns 371.00 ns] change: [-4.5087% -4.1494% -3.8349%] (p = 0.00 < 0.05) Performance has improved. Found 6 outliers among 100 measurements (6.00%) 2 (2.00%) low mild 1 (1.00%) high mild 3 (3.00%) high severe fine/gradient/extend/reflect_u8_neon time: [417.63 ns 418.73 ns 420.20 ns] change: [-6.1869% -5.5205% -4.6695%] (p = 0.00 < 0.05) Performance has improved. Found 15 outliers among 100 measurements (15.00%) 1 (1.00%) low mild 8 (8.00%) high mild 6 (6.00%) high severe fine/gradient/many_stops_u8_neon time: [479.07 ns 480.13 ns 481.45 ns] change: [-0.7523% -0.4523% -0.0884%] (p = 0.01 < 0.05) Change within noise threshold. Found 8 outliers among 100 measurements (8.00%) 1 (1.00%) low mild 5 (5.00%) high mild 2 (2.00%) high severe fine/gradient/transparent_u8_neon time: [459.30 ns 461.39 ns 463.68 ns] change: [-0.4103% +0.0785% +0.6946%] (p = 0.77 > 0.05) No change in performance detected. Found 10 outliers among 100 measurements (10.00%) 1 (1.00%) low mild 3 (3.00%) high mild 6 (6.00%) high severe ``` --------- Co-authored-by: Laurenz Stampfl <laurenz@canva.com> Co-authored-by: Alex Gemberg <gemberg@canva.com>
A GPU compute-centric 2D renderer
Vello is a 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:
Significant changes are documented in the changelog.
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.
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:
use vello::{ kurbo::{Affine, Circle}, peniko::{Color, Fill}, *, }; // Initialize wgpu and get handles let (width, height) = ...; let device: wgpu::Device = ...; let queue: wgpu::Queue = ...; let mut renderer = Renderer::new( &device, RendererOptions::default() ).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::from_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(...); let texture = device.create_texture(&...); // Render to a wgpu Texture renderer .render_to_texture( &device, &queue, &scene, &texture, &vello::RenderParams { base_color: palette::css::BLACK, // Background color width, height, antialiasing_method: AaConfig::Msaa16, }, ) .expect("Failed to render to a texture"); // Do things with `texture`, such as blitting it to the Surface using // wgpu::util::TextureBlitter
See the examples directory for code that integrates with frameworks like winit.
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.
A separate Linebender integration for rendering SVG files is available through vello_svg.
A separate Linebender integration for playing Lottie animations is available through velato.
A separate Linebender integration for rendering raw scenes or Lottie and SVG files in Bevy through bevy_vello.
Our examples are provided in separate packages in the examples directory. This allows them to have independent dependencies and faster builds. Examples must be selected using the --package (or -p) Cargo flag.
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
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.
Because Vello relies heavily on compute shaders, we rely on the emerging WebGPU standard to run on the web. Browser support for WebGPU is still evolving. Vello has been tested using production versions of Chrome, but WebGPU support in Firefox and Safari is still experimental. It may be necessary to use development browsers 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.
The with_winit example supports running on Android, using cargo apk.
cargo apk run -p with_winit --lib
[!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$HOMEto your home directory):
[package.metadata.android.signing.release] path = "$HOME/.android/debug.keystore" keystore_password = "android"
[!NOTE] As
cargo apkdoes 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_winitcurrently supports the environment variables:
VELLO_STATIC_LOG, which is equivalent toRUST_LOGVELLO_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
This version of Vello has been verified to compile with Rust 1.86 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
Discussion of Vello development happens in the Linebender Zulip, specifically the #vello channel. 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.
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.
Vello takes inspiration from many other rendering projects, including:
Licensed under either of
at your option.
In addition, all files in the vello_shaders/shader and vello_shaders/src/cpu directories and subdirectories thereof are alternatively licensed under the Unlicense (vello_shaders/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.
