glowRadius property
Radius of the directional specular sheen as a fraction of the button's shortest side.
This controls the shape-clipped, touch-tracking highlight that follows
the finger across the glass surface — iOS 26's .glassEffect(.interactive())
behaviour applied at the button level.
null(default): Native iOS 26 mode. Resolves to a wide, calibrated 1.6 radius with a soft sigma-16 Gaussian blur and subtle specular alpha, clipped strictly to shape via ShapeBorderClipper. The light washes smoothly across the button surface without producing a concentrated, pointy hotspot, matching Apple's touch-reactive glass reflection.0.0: Opt out. No directional sheen — the press brightens the whole surface evenly through ambientBaseLight only.> 0.0: Custom explicit radius. The glow is still clipped to shape but uses the supplied radius instead of the native default.
Note: The specular sheen is geometrically bounded by the button's
shape and can never escape the glass boundary. For grouped buttons,
use GlassButtonGroup — the whole platter shares one glow layer, so
dragging across buttons sweeps the highlight seamlessly from button to
button, matching iOS 26 GlassEffectContainer behaviour.
Defaults to null (native iOS 26 specular).
Implementation
final double? glowRadius;