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66 lines
1.5 KiB
Rust
66 lines
1.5 KiB
Rust
use crate::ui::scrollbar::draw_scrollbar;
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use std::cell::Cell;
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use tui::{backend::Backend, layout::Rect, Frame};
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pub struct VerticalScroll {
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top: Cell<usize>,
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max_top: Cell<usize>,
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}
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impl VerticalScroll {
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pub const fn new() -> Self {
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Self {
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top: Cell::new(0),
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max_top: Cell::new(0),
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}
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}
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pub fn get_top(&self) -> usize {
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self.top.get()
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}
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pub fn reset(&self) {
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self.top.set(0);
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}
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pub fn update(&self, selection: usize, selection_max: usize, visual_height: usize) -> usize {
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let new_top = calc_scroll_top(self.get_top(), visual_height, selection, selection_max);
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self.top.set(new_top);
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if visual_height == 0 {
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self.max_top.set(0);
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} else {
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let new_max = selection_max.saturating_sub(visual_height);
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self.max_top.set(new_max);
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}
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new_top
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}
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pub fn draw<B: Backend>(&self, f: &mut Frame<B>, r: Rect) {
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draw_scrollbar(f, r, self.max_top.get(), self.top.get());
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}
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}
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const fn calc_scroll_top(
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current_top: usize,
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height_in_lines: usize,
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selection: usize,
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selection_max: usize,
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) -> usize {
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if height_in_lines == 0 {
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return 0;
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}
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if selection_max <= height_in_lines {
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return 0;
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}
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if current_top + height_in_lines <= selection {
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selection.saturating_sub(height_in_lines) + 1
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} else if current_top > selection {
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selection
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} else {
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current_top
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}
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}
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