vello_tests/README.md

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# Vello Tests

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This is a development-only crate for testing the Sparse Strips renderers across
a corpus of reference images:

- CPU
- WGPU
- WASM32 WebGL

The `vello_test` proc macro will create a snapshot test for each supported
renderer target. See the below example usage.

```rs
// Draws a filled triangle into a 125x125 scene.
#[vello_test(width = 125, height = 125)]
fn filled_triangle(ctx: &mut impl Renderer) {
    let path = {
        let mut path = BezPath::new();
        path.move_to((5.0, 5.0));
        path.line_to((95.0, 50.0));
        path.line_to((5.0, 95.0));
        path.close_path();

        path
    };

    ctx.set_paint(LIME);
    ctx.fill_path(&path);
}
```

See all the attributes that can be passed to `vello_test` in
[`vello_dev_macros/src/test.rs`](vello_dev_macros/src/test.rs).

## Testing WebGL on the Browser

Requirements:

- on MacOS, a minimum Clang major version of 20 is required.

To run the `vello_tests` suite including the WebGL tests:

```sh
wasm-pack test --headless --chrome --features webgl --release
```

To debug the output images in webgl, run the same command without `--headless`.
Any tests that fail will have their diff image appended to the bottom of the
page.