Function paint_glass_body 

pub fn paint_glass_body(
    scene: &mut Scene,
    transform: Affine,
    rect: Rect,
    radius: f64,
    theme: &Theme,
    tier: &SelectionTier,
    opacity: f32,
)

Paint one selector’s body in the glass material: film, edge, and — for a lifted one — a lit inner rim.

opacity scales the whole material, for a caller animating a body in or out. It multiplies rather than replaces so a half-revealed pill is half of this material, not a different one.

Deliberately lays down no shadow — elevation and selection are different vocabularies (see selection_tier). What replaces it is the edge: a surface that reports its own light does not need a shadow to say it is a surface.