Function push_blended_edge 

pub fn push_blended_edge(
    mesh: &mut LineMesh<3>,
    a: Vec4,
    b: Vec4,
    arc_center: Vec4,
    color_a: [f32; 4],
    color_b: [f32; 4],
    width: f32,
    blend: f32,
    projection: &Projection<4>,
    body_pos_r3: Vec3,
    samples: usize,
    view_radius: f32,
)

Blends body-frame chords and arcs with blend in [0, 1]; arc radii interpolate about arc_center.