Constant libnotcurses_sys::NCALPHA_BG_ALPHA_MASK

pub const NCALPHA_BG_ALPHA_MASK: u32 = crate::bindings::ffi::NC_BG_ALPHA_MASK; // 0x3000_0000u32

Extract these bits to get the background alpha mask (NcAlphaBits)

See the detailed diagram at NcChannels

Note: This can also be used against a single NcChannel