in heatmap/src/heatmap.rs [286:298]
fn next(&mut self) -> Option<Window<'a>> {
if self.visited >= self.inner.slices.len() {
None
} else {
let bucket = self.inner.get_slice(self.index);
self.index += 1;
if self.index >= self.inner.slices.len() {
self.index = 0;
}
self.visited += 1;
bucket
}
}