pub(crate) fn pulse_alpha(t: f32) -> f32Expand description
Pulse alpha in 0..=1 for elapsed seconds since the splash appeared: a linear
ramp 0→1 over FADE_IN_S, then a PULSE_HZ sine between PULSE_MIN..PULSE_MAX
(the backdrop stays opaque; only the brain’s alpha breathes). Shared by both
backends.