README.md

Vega wgpu renderer

This repo holds an early stage prototype of what it could look like to build an alternative Vega visualization renderer in Rust using wgpu. This is not useful yet (and may never be).

We're exploring how general the various components are, and so the names and structures of crates are still changing. If you're interested in collaborating on a visualization renderer for a non-Vega application, please open an issue.

Try it out

Run native

To launch a wgpu rendered visualization in a native window, run the following:

cd sg2d-wgpu
cargo run

Build wasm

To build the example above to WASM + WebGL2, run the following:

cd examples/wgpu-winit
wasm-pack build --target web

Then open examples/wgpu-winit/index.html in a web browser.

Export PNG

The PngCanvas struct can be used to convert a scene graph to a PNG image headlessly. See the tests in vega-wgpu-renderer/tests/test_image_baselines.rs for usage.

Motivation

Vega currently ships with two renderers: svg (which outputs SVG) and canvas (which renders to HTML Canvas). The hypothesis is that Canvas rendering is expensive enough for charts with large marks that there will be substantial benefit to rendering on the GPU. Admittedly, more experimentation and benchmarking is still needed to justify this hypothesis. For this use case, the wgpu renderer would be compiled to WASM and registered with Vega as a third renderer type.

Separately, this is an important step in the direction of developing a fully native Vega renderer. Combined with VegaFusion, most of the logic for fully native rendering (starting with the Vega spec) will be available in Rust. There will be more work to do to update VegaFusion to generate scene graphs, but this is a definite possibility.

Short of supporting full native rendering, this wgpu renderer may be useful to vl-convert to accelerate PNG static image export, and to VegaFusion to support serverside rendering of large marks.

Testing

To start with, the most valuable contribution of this project is probably the testing infrastructure. By relying on vl-convert, a collection of input Vega specs are rendered to PNG and converted to scene graphs. The GPU rendered PNG images are then compared for similarity to the baselines using structural similarity. See the gen-test-data crate for more information.

Note: These tests aren't running on GitHub Actions yet due to a MakeWgpuAdapterError error that needs to be diagnosed.