Function visible_rows 

pub fn visible_rows(
    offset_y: f32,
    vh: f32,
    pad_t: f32,
    row_h: f32,
    rows: usize,
    overscan: usize,
) -> Range<usize> 

The half-open range of rows a container of rows rows, each row_h logical px tall, has any reason to build — those crossing the visible band, plus overscan on each side — given the geometry of the frame before. Pure arithmetic, exposed for views that build their own container instead of using uniform_list.

vh is the container’s height, and pad_t the padding above the first row. None geometry means no layout has resolved the container yet: the caller decides what the first frame builds.