Function capsule_polygon 

pub fn capsule_polygon(
    x1: f64,
    y1: f64,
    x2: f64,
    y2: f64,
    radius: f64,
    quad_segs: u32,
) -> Vec<(f64, f64)>

Filled capsule: segment (x1,y1)–(x2,y2) thickened by radius, round caps.