Function tick 

pub(crate) fn tick(clock: &mut f32, step: f32, delta_time: f32) -> bool

Accumulate delta_time into clock and report whether a step-long interval has passed, subtracting it from the clock if so.

At most one interval is consumed per call, so a long stall advances a fixed-sequence scene by one frame rather than skipping several. The leftover stays in the clock, so the sequence keeps pace over time.