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fix: scrollbar thumb not visible on long lists (#959)

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When displaying somewhat-long lists, the `Scrollbar` widget sometimes did not display a thumb character, and only the track will be visible.
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ThomasMiz 2024-02-20 16:24:33 -03:00 committed by GitHub
parent b0314c5731
commit 35e971f7eb
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1 changed files with 52 additions and 16 deletions
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68
src/widgets/scrollbar.rs
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@ -498,27 +498,32 @@ impl Scrollbar<'_> {
///
/// This method returns the length of the start, thumb, and end as a tuple.
fn part_lengths(&self, area: Rect, state: &mut ScrollbarState) -> (usize, usize, usize) {
let track_len = self.track_length_excluding_arrow_heads(area) as f64;
let viewport_len = self.viewport_length(state, area) as f64;
let track_length = self.track_length_excluding_arrow_heads(area) as f64;
let viewport_length = self.viewport_length(state, area) as f64;
let content_length = state.content_length as f64;
// Clamp the position to show at least one line of the content, even if the content is
let position = state.position.min(state.content_length - 1) as f64;
// Ensure that the position of the thumb is within the bounds of the content taking into
// account the content and viewport length. When the last line of the content is at the top
// of the viewport, the thumb should be at the bottom of the track.
let max_position = state.content_length.saturating_sub(1) as f64;
let start_position = (state.position as f64).clamp(0.0, max_position);
let max_viewport_position = max_position + viewport_length;
let end_position = start_position + viewport_length;
// vscode style scrolling behavior (allow scrolling past end of content)
let scrollable_content_len = content_length + viewport_len - 1.0;
let thumb_start = position * track_len / scrollable_content_len;
let thumb_end = (position + viewport_len) * track_len / scrollable_content_len;
// Calculate the start and end positions of the thumb. The size will be proportional to the
// viewport length compared to the total amount of possible visible rows.
let thumb_start = start_position * track_length / max_viewport_position;
let thumb_end = end_position * track_length / max_viewport_position;
// We round just the positions (instead of floor / ceil), and then calculate the sizes from
// those positions. Rounding the sizes instead causes subtle off by 1 errors.
let track_start_len = thumb_start.round() as usize;
let thumb_end = thumb_end.round() as usize;
// Make sure that the thumb is at least 1 cell long by ensuring that the start of the thumb
// is less than the track_len. We use the positions instead of the sizes and use nearest
// integer instead of floor / ceil to avoid problems caused by rounding errors.
let thumb_start = thumb_start.round().clamp(0.0, track_length - 1.0) as usize;
let thumb_end = thumb_end.round().clamp(0.0, track_length) as usize;
let thumb_len = thumb_end.saturating_sub(track_start_len);
let track_end_len = track_len as usize - track_start_len - thumb_len;
let thumb_length = thumb_end.saturating_sub(thumb_start).max(1);
let track_end_length = (track_length as usize).saturating_sub(thumb_start + thumb_length);
(track_start_len, thumb_len, track_end_len)
(thumb_start, thumb_length, track_end_length)
}
fn scollbar_area(&self, area: Rect) -> Rect {
@ -1053,4 +1058,35 @@ mod tests {
scrollbar_no_arrows.render(buffer.area, &mut buffer, &mut state);
assert_eq!(buffer, Buffer::with_lines(vec![expected]), "{description}");
}
/// Fixes <https://github.com/ratatui-org/ratatui/pull/959> which was a bug that would not
/// render a thumb when the viewport was very small in comparison to the content length.
#[rstest]
#[case("#----", 0, 100, "position_0")]
#[case("#----", 10, 100, "position_10")]
#[case("-#---", 20, 100, "position_20")]
#[case("-#---", 30, 100, "position_30")]
#[case("--#--", 40, 100, "position_40")]
#[case("--#--", 50, 100, "position_50")]
#[case("---#-", 60, 100, "position_60")]
#[case("---#-", 70, 100, "position_70")]
#[case("----#", 80, 100, "position_80")]
#[case("----#", 90, 100, "position_90")]
#[case("----#", 100, 100, "position_one_out_of_bounds")]
fn thumb_visible_on_very_small_track(
#[case] expected: &str,
#[case] position: usize,
#[case] content_length: usize,
#[case] description: &str,
scrollbar_no_arrows: Scrollbar,
) {
let size = expected.width() as u16;
let mut buffer = Buffer::empty(Rect::new(0, 0, size, 1));
let mut state = ScrollbarState::default()
.position(position)
.content_length(content_length)
.viewport_content_length(2);
scrollbar_no_arrows.render(buffer.area, &mut buffer, &mut state);
assert_eq!(buffer, Buffer::with_lines(vec![expected]), "{description}");
}
}