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pub struct ScrollState {
n_rows: usize,
max_n_rows_to_display: usize,
selected: Option<usize>,
offset: usize,
scroll_padding: usize,
max_scroll_padding: usize,
}
impl ScrollState {
pub fn new(n_rows: usize, selected: Option<usize>, max_scroll_padding: usize) -> Self {
Self {
n_rows,
max_n_rows_to_display: 0,
selected,
offset: selected.map_or(0, |selected| selected.saturating_sub(max_scroll_padding)),
scroll_padding: 0,
max_scroll_padding,
}
}
#[inline]
pub fn offset(&self) -> usize {
self.offset
}
fn update_offset(&mut self) {
let Some(selected) = self.selected else {
return;
};
let min_offset = (selected + self.scroll_padding)
.saturating_sub(self.max_n_rows_to_display.saturating_sub(1));
let max_offset = selected.saturating_sub(self.scroll_padding);
let global_max_offset = self.n_rows.saturating_sub(self.max_n_rows_to_display);
self.offset = self
.offset
.max(min_offset)
.min(max_offset)
.min(global_max_offset);
}
#[inline]
pub fn selected(&self) -> Option<usize> {
self.selected
}
pub fn set_selected(&mut self, selected: usize) {
self.selected = Some(selected);
self.update_offset();
}
pub fn select_next(&mut self) {
if let Some(selected) = self.selected {
self.set_selected((selected + 1).min(self.n_rows - 1));
}
}
pub fn select_previous(&mut self) {
if let Some(selected) = self.selected {
self.set_selected(selected.saturating_sub(1));
}
}
pub fn select_first(&mut self) {
if self.n_rows > 0 {
self.set_selected(0);
}
}
pub fn select_last(&mut self) {
if self.n_rows > 0 {
self.set_selected(self.n_rows - 1);
}
}
pub fn set_n_rows(&mut self, n_rows: usize) {
self.n_rows = n_rows;
if self.n_rows == 0 {
self.selected = None;
return;
}
self.set_selected(self.selected.map_or(0, |selected| selected.min(n_rows - 1)));
}
#[inline]
fn update_scroll_padding(&mut self) {
self.scroll_padding = (self.max_n_rows_to_display / 4).min(self.max_scroll_padding);
}
#[inline]
pub fn max_n_rows_to_display(&self) -> usize {
self.max_n_rows_to_display
}
pub fn set_max_n_rows_to_display(&mut self, max_n_rows_to_display: usize) {
self.max_n_rows_to_display = max_n_rows_to_display;
self.update_scroll_padding();
self.update_offset();
}
}
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