using a Lyon Path in a GeometryBuilder results in a panic

[db48x]

The resulting Mesh has a Vertex_Position attribute, but not a Vertex_Position_2D attribute:

[src/main.rs:70] meshes.get(&trail.mesh).unwrap() = Mesh {
    primitive_topology: TriangleList,
    attributes: {
        "Vertex_Normal": Float3([ … ]),
        "Vertex_Position": Float3([ … ]),
        "Vertex_Uv": Float2([ … ]),
    }
    indices: Some(U32([ … ])),
}

thread 'Compute Task Pool (4)' panicked at 'Attribute Vertex_Position_2D is required by shader, but not supplied by mesh. Either remove the attribute from the shader or supply the attribute (Vertex_Position_2D) to the mesh.', /home/db48x/.cargo/registry/src/github.com-1ecc6299db9ec823/bevy_render-0.5.0/src/pipeline/pipeline_compiler.rs:231:17

[db48x]

Though I suppose I could be doing something wrong. Perhaps we could work on an example with a system that modifies the shape that gets drawn?

[Nilirad]

bevy_prototype_lyon uses custom shaders with custom attributes. If you remove the Vertex_Normal attribute and change the Vertex_Position attribute with Vertex_Position_2D (it is a Float2) it may work. Also, the shader accepts also a Vertex_Color attribute.

You can also draw paths using the PathBuilder API or by implementing Geometry on a custom struct.

[db48x]

Yea, I was trying to use PathBuilder. However, I think the code was going wrong somehow. I think it was building the path correctly, but then retrieving the wrong mesh from somewhere and attempting to use it. Here’s the code I wrote:

fn trail_system(mut commands: Commands,
                mut meshes: ResMut<Assets<Mesh>>,
                mut q: Query<(Entity, &mut Trail, &mut Transform, &mut Handle<Mesh>)>) {
    for (e, mut tr, p, mut h) in q.iter_mut() {
        //dbg!(meshes.get_mut(&*h).unwrap());
        //dbg!(&h);
        //todo!();
        if tr.path.len() >= 32 {
            tr.path.resize(32, Vec3::new(f32::NAN, f32::NAN, f32::NAN));
        }
        tr.path.insert(0, p.translation);

        let mut geometry = GeometryBuilder::new();
        let mut path = PathBuilder::new();
        let points = tr.path.iter();
        path.move_to(Vec2::new(0.0, 0.0));
        for &p1 in points {
            let p1 = Vec2::from(p1 - p.translation);
            path.line_to(p1);
        }
        geometry.add(&path.build());
        geometry.add(&shapes::Circle {
            radius: 2.0,
            center: Vec2::ZERO,
        });
        let trail = geometry.build(
            ShapeColors::new(Color::RED),
            DrawMode::Fill(FillOptions::DEFAULT),
            *p,
        );
        //let mesh = meshes.get_mut(dbg!(&trail.mesh)).unwrap();
        //let vertices = mesh.attribute_mut(Mesh::ATTRIBUTE_POSITION);
        //if let Some(bevy::render::mesh::VertexAttributeValues::Float3(vs)) = vertices {
        //    let mut new_vs: Vec<[f32; 2]> = Vec::with_capacity(vs.len());
        //    let mut new_colors: Vec<[f32; 4]> = Vec::with_capacity(vs.len());
        //    for v in vs {
        //        new_vs.push(v[0..2].try_into().expect("!"));
        //        new_colors.push([1.0, 0.0, 1.0, 1.0]);
        //    }
        //    const ATTRIBUTE_POSITION_2D: &str = "Vertex_Position_2D";
        //    mesh.set_attribute(ATTRIBUTE_POSITION_2D, new_vs);
        //    mesh.set_attribute(Mesh::ATTRIBUTE_COLOR, new_colors);
        //}
        //dbg!(&mesh);
        *h = trail.mesh;
        //commands.entity(e).insert_bundle(trail);
        //todo!();
    }
}