bad triangle panic with variable line width

[luiswirth]

This is probably still #819, but in combination with an attribute to support variable line width.
This wasn't fixed by #820

use lyon::{
    geom::point,
    lyon_tessellation::{geometry_builder::simple_builder, StrokeOptions},
    path::{LineCap, Path},
    tessellation::{StrokeTessellator, VertexBuffers},
};

const DEFAULT_STROKE_WIDTH: f32 = 1.0;
const STROKE_WIDTH_ATTRIBUTE: lyon::path::AttributeIndex = 0;

fn path() -> Path {
    let mut path = Path::builder_with_attributes(1);
    path.begin(point(-45.192276, -69.800575), &[DEFAULT_STROKE_WIDTH]);
    path.line_to(point(-45.164116, -69.84931), &[DEFAULT_STROKE_WIDTH]);
    path.line_to(point(-45.135952, -69.90564), &[DEFAULT_STROKE_WIDTH]);
    path.line_to(point(-45.10779, -69.93248), &[DEFAULT_STROKE_WIDTH]);
    path.line_to(point(-45.052788, -69.96064), &[DEFAULT_STROKE_WIDTH]);
    path.line_to(point(-45.026604, -69.898155), &[DEFAULT_STROKE_WIDTH]);

    path.end(false);
    path.build()
}

fn main() {
    let mut stroker = StrokeTessellator::new();

    let options = StrokeOptions::default()
        .with_tolerance(0.001)
        .with_line_cap(LineCap::Round)
        .with_variable_line_width(STROKE_WIDTH_ATTRIBUTE);

    let path = path();
    let mut mesh = VertexBuffers::new();
    let mut builder = simple_builder(&mut mesh);
    stroker
        .tessellate_path(&path, &options, &mut builder)
        .unwrap();
}

panics with

bad triangle VertexId(4) VertexId(7) VertexId(7)
thread 'main' panicked at 'assertion failed: b != c', /home/luis/.local/share/cargo/registry/src/github.com-1ecc6299db9ec823/lyon_tessellation-1.0.3/src/geometry_builder.rs:461:9

[nical]

That's a different issue. The other one was producing invalid vertex ids due to some computation being skipped, while this one has triangles with the same vertex twice which should not happen.

Thanks for filing this and double thanks for the reduced test case, I'll look into it soon.

[luiswirth]

Thanks 👍🏾 🎉