Fix scroll up

examples/simple.rs

@@ -52,7 +52,7 @@ impl App {
 
     fn draw(&mut self, terminal: &mut Terminal<impl Backend>) -> Result<()> {
         terminal.draw(|frame| {
-            frame.render_widget(self, frame.size());
+            frame.render_widget(self, frame.area());
         })?;
         Ok(())
     }

examples/var_sizes.rs

@@ -98,7 +98,7 @@ impl Widget for &mut App {
     where
         Self: Sized,
     {
-        let sizes = vec![4, 6, 5, 4, 3, 3, 6, 5, 7, 3, 6, 9, 4, 6];
+        let sizes = vec![100, 100, 4, 6, 5, 4, 3, 3, 6, 5, 7, 3, 6, 9, 10, 4, 4, 6];
         let item_count = sizes.len();
 
         let block = Block::default().borders(Borders::ALL).title("Outer block");
@@ -129,7 +129,7 @@ impl App {
 pub fn run_app<B: Backend>(terminal: &mut Terminal<B>, mut app: App) -> io::Result<()> {
     loop {
         terminal.draw(|frame| {
-            frame.render_widget(&mut app, frame.size());
+            frame.render_widget(&mut app, frame.area());
         })?;
 
         if let Event::Key(key) = event::read()? {
@@ -144,8 +144,3 @@ pub fn run_app<B: Backend>(terminal: &mut Terminal<B>, mut app: App) -> io::Resu
         }
     }
 }
-
-// pub fn ui(f: &mut Frame, app: App) {
-//     // let list = app.list;
-//     f.render_stateful_widget_ref(app.list, f.size(), &mut app.state);
-// }

src/legacy/utils.rs

@@ -28,16 +28,16 @@ pub(crate) fn layout_on_viewport<T: PreRender>(
 
     // If the selected value is smaller than the offset, we roll
     // the offset so that the selected value is at the top
-    if selected < state.offset {
-        state.offset = selected;
+    if selected < state.view_state.offset {
+        state.view_state.offset = selected;
     }
 
     let mut main_axis_size_cache: HashMap<usize, u16> = HashMap::new();
 
     // Check if the selected item is in the current view
-    let (mut y, mut index) = (0, state.offset);
+    let (mut y, mut index) = (0, state.view_state.offset);
     let mut found = false;
-    for widget in widgets.iter_mut().skip(state.offset) {
+    for widget in widgets.iter_mut().skip(state.view_state.offset) {
         // Get the main axis size of the widget.
         let is_selected = state.selected.map_or(false, |j| index == j);
         let context = PreRenderContext::new(is_selected, cross_axis_size, scroll_axis, index);
@@ -101,7 +101,7 @@ pub(crate) fn layout_on_viewport<T: PreRender>(
                     truncated_by: main_axis_size.saturating_sub(dy),
                 },
             );
-            state.offset = index;
+            state.view_state.offset = index;
             break;
         }
 
@@ -125,85 +125,3 @@ pub(crate) struct ViewportLayout {
     pub(crate) main_axis_size: u16,
     pub(crate) truncated_by: u16,
 }
-
-#[cfg(test)]
-mod tests {
-    use ratatui::{
-        prelude::*,
-        widgets::{Block, Borders},
-    };
-
-    use super::*;
-
-    struct TestItem {
-        main_axis_size: u16,
-    }
-
-    impl Widget for TestItem {
-        fn render(self, area: Rect, buf: &mut Buffer)
-        where
-            Self: Sized,
-        {
-            Block::default().borders(Borders::ALL).render(area, buf);
-        }
-    }
-
-    impl PreRender for TestItem {
-        fn pre_render(&mut self, _context: &PreRenderContext) -> u16 {
-            self.main_axis_size
-        }
-    }
-
-    macro_rules! update_view_port_tests {
-        ($($name:ident:
-        [
-           $given_offset:expr,
-           $given_selected:expr,
-           $given_sizes:expr,
-           $given_max_size:expr
-        ],
-        [
-           $expected_offset:expr,
-           $expected_sizes:expr
-        ],)*) => {
-        $(
-            #[test]
-            fn $name() {
-                // given
-                let mut given_state = ListState {
-                    offset: $given_offset,
-                    selected: $given_selected,
-                    num_elements: $given_sizes.len(),
-                    circular: true,
-                };
-
-                //when
-                let mut widgets: Vec<TestItem> = $given_sizes
-                    .into_iter()
-                    .map(|main_axis_size| TestItem {
-                        main_axis_size: main_axis_size as u16,
-                    })
-                    .collect();
-                let scroll_axis = ScrollAxis::default();
-                let layouts = layout_on_viewport(&mut given_state, &mut widgets, $given_max_size, 0, scroll_axis);
-                let offset = given_state.offset;
-
-                // then
-                let main_axis_sizes: Vec<u16> = layouts.iter().map(|x| x.main_axis_size).collect();
-                assert_eq!(offset, $expected_offset);
-                assert_eq!(main_axis_sizes, $expected_sizes);
-            }
-        )*
-        }
-    }
-
-    update_view_port_tests! {
-        happy_path: [0, Some(0), vec![2, 3], 6], [0, vec![2, 3]],
-        empty_list: [0, None, Vec::<u16>::new(), 4], [0, vec![]],
-        update_offset_down: [0, Some(2), vec![2, 3, 3], 6], [1, vec![3, 3]],
-        update_offset_up: [1, Some(0), vec![2, 3, 3], 6], [0, vec![2, 3, 1]],
-        truncate_bottom: [0, Some(0), vec![2, 3], 4], [0, vec![2, 2]],
-        truncate_top: [0, Some(1), vec![2, 3], 4], [0, vec![1, 3]],
-        num_elements: [0, None, vec![1, 1, 1, 1, 1], 3], [0, vec![1, 1, 1]],
-    }
-}

src/legacy/widget.rs

@@ -144,7 +144,10 @@ impl<'a, T: PreRender> StatefulWidget for List<'a, T> {
         // Drain out elements that are shown on the view port from the vector of
         // all elements.
         let num_items_viewport = viewport_layouts.len();
-        let (start, end) = (state.offset, num_items_viewport + state.offset);
+        let (start, end) = (
+            state.view_state.offset,
+            num_items_viewport + state.view_state.offset,
+        );
         let items_viewport = items.drain(start..end);
 
         // The starting coordinates of the current item

src/state.rs

@@ -4,9 +4,6 @@ pub struct ListState {
     /// The selected item. If `None`, no item is currently selected.
     pub selected: Option<usize>,
 
-    /// The index of the first item displayed on the screen.
-    pub(crate) offset: usize,
-
     /// The total number of elements in the list. This is necessary to correctly
     /// handle item selection.
     pub(crate) num_elements: usize,
@@ -16,15 +13,28 @@ pub struct ListState {
     ///
     /// True by default.
     pub(crate) circular: bool,
+
+    /// The state for the viewport. Keeps track which item to show
+    /// first and how much it is truncated.
+    pub(crate) view_state: ViewState,
+}
+
+#[derive(Debug, Clone, Default, Eq, PartialEq)]
+pub(crate) struct ViewState {
+    /// The index of the first item displayed on the screen.
+    pub(crate) offset: usize,
+
+    /// The truncation in rows/columns of the first item displayed on the screen.
+    pub(crate) first_truncated: u16,
 }
 
 impl Default for ListState {
     fn default() -> Self {
         Self {
             selected: None,
-            offset: 0,
             num_elements: 0,
             circular: true,
+            view_state: ViewState::default(),
         }
     }
 }
@@ -48,7 +58,7 @@ impl ListState {
     pub fn select(&mut self, index: Option<usize>) {
         self.selected = index;
         if index.is_none() {
-            self.offset = 0;
+            self.view_state.offset = 0;
         }
     }