toolbarOpacity property
How opaque the toolbar part of the app bar is.
A value of 1.0 is fully opaque, and a value of 0.0 is fully transparent.
Typically, this value is not changed from its default value (1.0). It is used by SliverGFAppBar to animate the opacity of the toolbar when the app bar is scrolled.
Implementation
final double toolbarOpacity;