Move logic from ScrollView to ScrollCore

src/cursive.rs

@@ -224,7 +224,7 @@ impl Cursive {
 
     /// Show the debug console.
     ///
-    /// Currently, this will show logs if [`::logger::init()`] was called.
+    /// Currently, this will show logs if [`logger::init()`](crate::logger::init()) was called.
     pub fn show_debug_console(&mut self) {
         self.add_layer(
             views::Dialog::around(views::ScrollView::new(views::IdView::new(

src/logger.rs

@@ -52,7 +52,8 @@ impl log::Log for CursiveLogger {
 ///
 /// Make sure this is the only logger your are using.
 ///
-/// Use a [`::views::DebugView`] to see the logs, or use [`::Cursive::toggle_debug_console()`].
+/// Use a [`DebugView`](crate::views::DebugView) to see the logs, or use
+/// [`Cursive::toggle_debug_console()`](crate::Cursive::toggle_debug_console()).
 pub fn init() {
     // TODO: Configure the deque size?
     LOGS.lock().unwrap().reserve(1_000);

src/view/mod.rs

@@ -51,7 +51,8 @@ mod view_trait;
 // Helper bases
 mod boxable;
 mod identifiable;
-mod scroll;
+pub mod scroll;
+mod scroll_base;
 mod scrollable;
 
 mod into_boxed_view;
@@ -63,7 +64,7 @@ pub use self::identifiable::Identifiable;
 pub use self::into_boxed_view::IntoBoxedView;
 pub use self::margins::Margins;
 pub use self::position::{Offset, Position};
-pub use self::scroll::{ScrollBase, ScrollStrategy};
+pub use self::scroll_base::{ScrollBase, ScrollStrategy};
 pub use self::scrollable::Scrollable;
 pub use self::size_cache::SizeCache;
 pub use self::size_constraint::SizeConstraint;

src/view/scroll_base.rs

@@ -0,0 +1,316 @@
+use crate::div::div_up;
+use crate::theme::ColorStyle;
+use crate::vec::Vec2;
+use crate::Printer;
+use std::cmp::{max, min};
+
+/// Provide scrolling functionalities to a view.
+///
+/// You're not supposed to use this directly,
+/// but it can be helpful if you create your own Views.
+#[derive(Default, Debug)]
+pub struct ScrollBase {
+    /// First line visible
+    pub start_line: usize,
+
+    /// Content height
+    pub content_height: usize,
+
+    /// Number of lines displayed
+    pub view_height: usize,
+
+    /// Padding for the scrollbar
+    ///
+    /// If present, the scrollbar will be shifted
+    /// `scrollbar_offset` columns to the left.
+    ///
+    /// (Useful when each item includes its own side borders,
+    /// to draw the scrollbar inside.)
+    pub scrollbar_offset: usize,
+
+    /// Blank between the text and the scrollbar.
+    pub right_padding: usize,
+
+    /// Initial position of the cursor when dragging.
+    pub thumb_grab: Option<usize>,
+}
+
+/// Defines the scrolling behaviour on content or size change
+#[derive(Debug)]
+pub enum ScrollStrategy {
+    /// Keeps the same row number
+    KeepRow,
+    /// Sticks to the top.
+    StickToTop,
+    /// Sticks to the bottom of the view.
+    StickToBottom,
+}
+
+impl Default for ScrollStrategy {
+    fn default() -> Self {
+        ScrollStrategy::KeepRow
+    }
+}
+
+impl ScrollBase {
+    /// Creates a new, uninitialized scrollbar.
+    pub fn new() -> Self {
+        ScrollBase {
+            start_line: 0,
+            content_height: 0,
+            view_height: 0,
+            scrollbar_offset: 0,
+            right_padding: 1,
+            thumb_grab: None,
+        }
+    }
+
+    /// Shifts the scrollbar toward the inside of the view.
+    ///
+    /// Used by views that draw their side borders in the children.
+    /// Pushing the scrollbar to the left allows it to stay inside
+    /// the borders.
+    pub fn scrollbar_offset(mut self, offset: usize) -> Self {
+        self.scrollbar_offset = offset;
+        self
+    }
+
+    /// Sets the number of blank cells between the text and the scrollbar.
+    ///
+    /// Defaults to 1.
+    pub fn right_padding(mut self, padding: usize) -> Self {
+        self.right_padding = padding;
+        self
+    }
+
+    /// Call this method whem the content or the view changes.
+    pub fn set_heights(&mut self, view_height: usize, content_height: usize) {
+        self.view_height = view_height;
+        self.content_height = content_height;
+
+        // eprintln!("Setting heights: {} in {}", content_height, view_height);
+
+        if self.scrollable() {
+            self.start_line =
+                min(self.start_line, self.content_height - self.view_height);
+        } else {
+            self.start_line = 0;
+        }
+    }
+
+    /// Returns `TRUE` if the view needs to scroll.
+    pub fn scrollable(&self) -> bool {
+        self.view_height < self.content_height
+    }
+
+    /// Returns `TRUE` unless we are at the top.
+    pub fn can_scroll_up(&self) -> bool {
+        self.start_line > 0
+    }
+
+    /// Returns `TRUE` unless we are at the bottom.
+    pub fn can_scroll_down(&self) -> bool {
+        self.start_line + self.view_height < self.content_height
+    }
+
+    /// Scroll to the top of the view.
+    pub fn scroll_top(&mut self) {
+        self.start_line = 0;
+    }
+
+    /// Makes sure that the given line is visible, scrolling if needed.
+    pub fn scroll_to(&mut self, y: usize) {
+        if y >= self.start_line + self.view_height {
+            self.start_line = 1 + y - self.view_height;
+        } else if y < self.start_line {
+            self.start_line = y;
+        }
+    }
+
+    /// Scroll to the bottom of the view.
+    pub fn scroll_bottom(&mut self) {
+        if self.scrollable() {
+            self.start_line = self.content_height - self.view_height;
+        }
+    }
+
+    /// Scroll down by the given number of line.
+    ///
+    /// Never further than the bottom of the view.
+    pub fn scroll_down(&mut self, n: usize) {
+        if self.scrollable() {
+            self.start_line = min(
+                self.start_line + n,
+                self.content_height - self.view_height,
+            );
+        }
+    }
+
+    /// Scrolls down until the scrollbar thumb is at the given location.
+    pub fn scroll_to_thumb(&mut self, thumb_y: usize, thumb_height: usize) {
+        // The min() is there to stop at the bottom of the content.
+        // The saturating_sub is there to stop at the bottom of the content.
+        // eprintln!("Scrolling to {}", thumb_y);
+        self.start_line = min(
+            div_up(
+                (1 + self.content_height - self.view_height) * thumb_y,
+                self.view_height - thumb_height + 1,
+            ),
+            self.content_height - self.view_height,
+        );
+    }
+
+    /// Scroll up by the given number of lines.
+    ///
+    /// Never above the top of the view.
+    pub fn scroll_up(&mut self, n: usize) {
+        if self.scrollable() {
+            self.start_line -= min(self.start_line, n);
+        }
+    }
+
+    /// Starts scrolling from the given cursor position.
+    pub fn start_drag(&mut self, position: Vec2, width: usize) -> bool {
+        // First: are we on the correct column?
+        let scrollbar_x = self.scrollbar_x(width);
+        // eprintln!("Grabbed {} for {}", position.x, scrollbar_x);
+        if position.x != scrollbar_x {
+            return false;
+        }
+
+        // Now, did we hit the thumb? Or should we direct-jump?
+        let height = self.scrollbar_thumb_height();
+        let thumb_y = self.scrollbar_thumb_y(height);
+
+        if position.y >= thumb_y && position.y < thumb_y + height {
+            // Grabbed!
+            self.thumb_grab = Some(position.y - thumb_y);
+        } else {
+            // Just jump a bit...
+            self.thumb_grab = Some((height - 1) / 2);
+            // eprintln!("Grabbed at {}", self.thumb_grab);
+            self.drag(position);
+        }
+
+        true
+    }
+
+    /// Keeps scrolling by dragging the cursor.
+    pub fn drag(&mut self, position: Vec2) {
+        // Our goal is self.scrollbar_thumb_y()+thumb_grab == position.y
+        // Which means that position.y is the middle of the scrollbar.
+        // eprintln!("Dragged: {:?}", position);
+        // eprintln!("thumb: {:?}", self.thumb_grab);
+        if let Some(grab) = self.thumb_grab {
+            let height = self.scrollbar_thumb_height();
+            self.scroll_to_thumb(position.y.saturating_sub(grab), height);
+        }
+    }
+
+    /// Returns `true` if we are in the process of dragging the scroll thumb.
+    pub fn is_dragging(&self) -> bool {
+        self.thumb_grab.is_some()
+    }
+
+    /// Stops grabbing the scrollbar.
+    pub fn release_grab(&mut self) {
+        self.thumb_grab = None;
+    }
+
+    /// Draws the scroll bar and the content using the given drawer.
+    ///
+    /// `line_drawer` will be called once for each line that needs to be drawn.
+    /// It will be given the absolute ID of the item to draw..
+    /// It will also be given a printer with the correct offset,
+    /// so it should only print on the first line.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use cursive::view::ScrollBase;
+    /// # use cursive::Printer;
+    /// # use cursive::theme;
+    /// # use cursive::backend;
+    /// # let scrollbase = ScrollBase::new();
+    /// # let b = backend::dummy::Backend::init();
+    /// # let t = theme::load_default();
+    /// # let printer = Printer::new((5,1), &t, &*b);
+    /// # let printer = &printer;
+    /// let lines = ["Line 1", "Line number 2"];
+    /// scrollbase.draw(printer, |printer, i| {
+    ///     printer.print((0,0), lines[i]);
+    /// });
+    /// ```
+    pub fn draw<F>(&self, printer: &Printer<'_, '_>, line_drawer: F)
+    where
+        F: Fn(&Printer<'_, '_>, usize),
+    {
+        if self.view_height == 0 {
+            return;
+        }
+        // Print the content in a sub_printer
+        let max_y =
+            min(self.view_height, self.content_height - self.start_line);
+        let w = if self.scrollable() {
+            // We have to remove the bar width and the padding.
+            printer.size.x.saturating_sub(1 + self.right_padding)
+        } else {
+            printer.size.x
+        };
+
+        for y in 0..max_y {
+            // Y is the actual coordinate of the line.
+            // The item ID is then Y + self.start_line
+            line_drawer(
+                &printer.offset((0, y)).cropped((w, 1)),
+                y + self.start_line,
+            );
+        }
+
+        // And draw the scrollbar if needed
+        if self.view_height < self.content_height {
+            // We directly compute the size of the scrollbar
+            // (that way we avoid using floats).
+            // (ratio) * max_height
+            // Where ratio is ({start or end} / content.height)
+            let height = self.scrollbar_thumb_height();
+            let start = self.scrollbar_thumb_y(height);
+
+            let color = if printer.focused {
+                ColorStyle::highlight()
+            } else {
+                ColorStyle::highlight_inactive()
+            };
+
+            let scrollbar_x = self.scrollbar_x(printer.size.x);
+            // eprintln!("Drawing bar at x={}", scrollbar_x);
+
+            // The background
+            printer.print_vline((scrollbar_x, 0), printer.size.y, "|");
+
+            // The scrollbar thumb
+            printer.with_color(color, |printer| {
+                printer.print_vline((scrollbar_x, start), height, "▒");
+            });
+        }
+    }
+
+    /// Returns the X position of the scrollbar, given the size available.
+    ///
+    /// Note that this does not depend whether or
+    /// not a scrollbar will actually be present.
+    pub fn scrollbar_x(&self, total_size: usize) -> usize {
+        total_size.saturating_sub(1 + self.scrollbar_offset)
+    }
+
+    /// Returns the height of the scrollbar thumb.
+    pub fn scrollbar_thumb_height(&self) -> usize {
+        max(1, self.view_height * self.view_height / self.content_height)
+    }
+
+    /// Returns the y position of the scrollbar thumb.
+    pub fn scrollbar_thumb_y(&self, scrollbar_thumb_height: usize) -> usize {
+        let steps = self.view_height - scrollbar_thumb_height + 1;
+        steps * self.start_line / (1 + self.content_height - self.view_height)
+    }
+}

src/view/scrollable.rs

@@ -3,7 +3,7 @@ use crate::views::ScrollView;
 
 /// Makes a view wrappable in a [`ScrollView`].
 ///
-/// [`ScrollView`]: ::views::ScrollView
+/// [`ScrollView`]: crate::views::ScrollView
 pub trait Scrollable: View + Sized {
     /// Wraps `self` in a `ScrollView`.
     fn scrollable(self) -> ScrollView<Self> {

src/views/scroll_view.rs

@@ -1,55 +1,15 @@
-use std::cmp::min;
-
-use crate::direction::{Direction, Orientation};
-use crate::event::{AnyCb, Event, EventResult, Key, MouseButton, MouseEvent};
+use crate::direction::Direction;
+use crate::event::{AnyCb, Event, EventResult};
 use crate::rect::Rect;
-use crate::theme::ColorStyle;
-use crate::view::{ScrollStrategy, Selector, SizeCache, View};
-use crate::{Printer, Vec2, With, XY};
+use crate::view::{scroll, ScrollStrategy, Selector, View};
+use crate::{Printer, Vec2, With};
 
 /// Wraps a view in a scrollable area.
 pub struct ScrollView<V> {
     /// The wrapped view.
     inner: V,
 
-    /// This is the size the child thinks we're giving him.
-    inner_size: Vec2,
-
-    /// Offset into the inner view.
-    ///
-    /// Our `(0,0)` will be inner's `offset`
-    offset: Vec2,
-
-    /// What was our own size last time we checked.
-    ///
-    /// This includes scrollbars, if any.
-    last_size: Vec2,
-
-    /// Are we scrollable in each direction?
-    enabled: XY<bool>,
-
-    /// Should we show scrollbars?
-    ///
-    /// Even if this is true, no scrollbar will be printed if we don't need to
-    /// scroll.
-    ///
-    /// TODO: have an option to always show the scrollbar.
-    /// TODO: have an option to show scrollbar on top/left.
-    show_scrollbars: bool,
-
-    /// How much padding should be between content and scrollbar?
-    ///
-    /// scrollbar_padding.x is the horizontal padding before the vertical scrollbar.
-    scrollbar_padding: Vec2,
-
-    /// Initial position of the cursor when dragging.
-    thumb_grab: Option<(Orientation, usize)>,
-
-    /// We keep the cache here so it can be busted when we change the content.
-    size_cache: Option<XY<SizeCache>>,
-
-    /// Defines how to update the offset when the view size changes.
-    scroll_strategy: ScrollStrategy,
+    core: scroll::ScrollCore,
 }
 
 impl<V> ScrollView<V>
@@ -60,21 +20,13 @@ where
     pub fn new(inner: V) -> Self {
         ScrollView {
             inner,
-            inner_size: Vec2::zero(),
-            offset: Vec2::zero(),
-            last_size: Vec2::zero(),
-            enabled: XY::new(false, true),
-            show_scrollbars: true,
-            scrollbar_padding: Vec2::new(1, 0),
-            thumb_grab: None,
-            size_cache: None,
-            scroll_strategy: ScrollStrategy::KeepRow,
+            core: scroll::ScrollCore::new(),
         }
     }
 
     /// Returns the viewport in the inner content.
     pub fn content_viewport(&self) -> Rect {
-        Rect::from_size(self.offset, self.available_size())
+        self.core.content_viewport()
     }
 
     /// Defines the way scrolling is adjusted on content or size change.
@@ -85,8 +37,7 @@ where
     /// It is reset to `ScrollStrategy::KeepRow` whenever the user scrolls
     /// manually.
     pub fn set_scroll_strategy(&mut self, strategy: ScrollStrategy) {
-        self.scroll_strategy = strategy;
-        self.adjust_scroll();
+        self.core.set_scroll_strategy(strategy);
     }
 
     /// Defines the way scrolling is adjusted on content or size change.
@@ -100,7 +51,7 @@ where
     ///
     /// Defaults to `true`.
     pub fn set_show_scrollbars(&mut self, show_scrollbars: bool) {
-        self.show_scrollbars = show_scrollbars;
+        self.core.set_show_scrollbars(show_scrollbars);
     }
 
     /// Control whether scroll bars are visibile.
@@ -115,24 +66,21 @@ where
     where
         S: Into<Vec2>,
     {
-        let max_offset = self.inner_size.saturating_sub(self.available_size());
-        self.offset = offset.into().or_min(max_offset);
+        self.core.set_offset(offset);
     }
 
     /// Controls whether this view can scroll vertically.
     ///
     /// Defaults to `true`.
     pub fn set_scroll_y(&mut self, enabled: bool) {
-        self.enabled.y = enabled;
-        self.invalidate_cache();
+        self.core.set_scroll_y(enabled);
     }
 
     /// Controls whether this view can scroll horizontally.
     ///
     /// Defaults to `false`.
     pub fn set_scroll_x(&mut self, enabled: bool) {
-        self.enabled.x = enabled;
-        self.invalidate_cache();
+        self.core.set_scroll_x(enabled);
     }
 
     /// Controls whether this view can scroll vertically.
@@ -155,272 +103,22 @@ where
 
     /// Programmatically scroll to the top of the view.
     pub fn scroll_to_top(&mut self) {
-        let curr_x = self.offset.x;
-        self.set_offset((curr_x, 0));
+        self.core.scroll_to_top();
     }
 
     /// Programmatically scroll to the bottom of the view.
     pub fn scroll_to_bottom(&mut self) {
-        let max_y = self.inner_size.saturating_sub(self.available_size()).y;
-        let curr_x = self.offset.x;
-        self.set_offset((curr_x, max_y));
+        self.core.scroll_to_bottom();
     }
 
     /// Programmatically scroll to the leftmost side of the view.
     pub fn scroll_to_left(&mut self) {
-        let curr_y = self.offset.y;
-        self.set_offset((0, curr_y));
+        self.core.scroll_to_left();
     }
 
     /// Programmatically scroll to the rightmost side of the view.
     pub fn scroll_to_right(&mut self) {
-        let max_x = self.inner_size.saturating_sub(self.available_size()).x;
-        let curr_y = self.offset.y;
-        self.set_offset((max_x, curr_y));
-    }
-
-    /// Clears the cache.
-    fn invalidate_cache(&mut self) {
-        self.size_cache = None;
-    }
-
-    /// Returns for each axis if we are scrolling.
-    fn is_scrolling(&self) -> XY<bool> {
-        self.inner_size.zip_map(self.last_size, |i, s| i > s)
-    }
-
-    /// Stops grabbing the scrollbar.
-    fn release_grab(&mut self) {
-        self.thumb_grab = None;
-    }
-
-    /// Returns the size taken by the scrollbars.
-    ///
-    /// Will be zero in axis where we're not scrolling.
-    ///
-    /// The scrollbar_size().x will be the horizontal space taken by the vertical scrollbar.
-    fn scrollbar_size(&self) -> Vec2 {
-        self.is_scrolling()
-            .swap()
-            .select_or(self.scrollbar_padding + (1, 1), Vec2::zero())
-    }
-
-    /// Returns the size available for the child view.
-    fn available_size(&self) -> Vec2 {
-        if self.show_scrollbars {
-            self.last_size.saturating_sub(self.scrollbar_size())
-        } else {
-            self.last_size
-        }
-    }
-
-    /// Compute the size we would need.
-    ///
-    /// Given the constraints, and the axis that need scrollbars.
-    ///
-    /// Returns `(inner_size, size, scrollable)`.
-    fn sizes_when_scrolling(
-        &mut self, constraint: Vec2, scrollable: XY<bool>, strict: bool,
-    ) -> (Vec2, Vec2, XY<bool>) {
-        // This is the size taken by the scrollbars.
-        let scrollbar_size = scrollable
-            .swap()
-            .select_or(self.scrollbar_padding + (1, 1), Vec2::zero());
-
-        let available = constraint.saturating_sub(scrollbar_size);
-
-        // This the ideal size for the child. May not be what he gets.
-        let inner_size = self.inner.required_size(available);
-
-        // Where we're "enabled", accept the constraints.
-        // Where we're not, just forward inner_size.
-        let size = self.enabled.select_or(
-            Vec2::min(inner_size + scrollbar_size, constraint),
-            inner_size + scrollbar_size,
-        );
-
-        // In strict mode, there's no way our size is over constraints.
-        let size = if strict {
-            size.or_min(constraint)
-        } else {
-            size
-        };
-
-        // On non-scrolling axis, give inner_size the available space instead.
-        let inner_size = self
-            .enabled
-            .select_or(inner_size, size.saturating_sub(scrollbar_size));
-
-        let new_scrollable = inner_size.zip_map(size, |i, s| i > s);
-
-        (inner_size, size, new_scrollable)
-    }
-
-    /// Starts scrolling from the cursor position.
-    ///
-    /// Returns `true` if the event was consumed.
-    fn start_drag(&mut self, position: Vec2) -> bool {
-        // For each scrollbar, how far it is.
-        let scrollbar_pos = self.last_size.saturating_sub((1, 1));
-        let lengths = self.scrollbar_thumb_lengths();
-        let offsets = self.scrollbar_thumb_offsets(lengths);
-        let available = self.available_size();
-
-        // This is true for Y if we grabbed the vertical scrollbar
-        // More specifically, we need both (for instance for the vertical bar):
-        // * To be in the right column: X == scrollbar_pos
-        // * To be in the right range: Y < available
-        let grabbed = position
-            .zip_map(scrollbar_pos, |p, s| p == s)
-            .swap()
-            .and(position.zip_map(available, |p, a| p < a));
-
-        // Iterate on axises, and keep the one we grabbed.
-        if let Some((orientation, pos, length, offset)) =
-            XY::zip4(Orientation::pair(), position, lengths, offsets)
-                .keep(grabbed.and(self.enabled))
-                .into_iter()
-                .filter_map(|x| x)
-                .next()
-        {
-            if pos >= offset && pos < offset + length {
-                // We grabbed the thumb! Now scroll from that position.
-                self.thumb_grab = Some((orientation, pos - offset));
-            } else {
-                // We hit the scrollbar, outside of the thumb.
-                // Let's move the middle there.
-                self.thumb_grab = Some((orientation, (length - 1) / 2));
-                self.drag(position);
-            }
-
-            return true;
-        }
-
-        false
-    }
-
-    /// Called when a mouse drag is detected.
-    fn drag(&mut self, position: Vec2) {
-        // Only do something if we grabbed something before.
-        if let Some((orientation, grab)) = self.thumb_grab {
-            self.scroll_to_thumb(
-                orientation,
-                position.get(orientation).saturating_sub(grab),
-            );
-        }
-    }
-
-    fn scroll_to_thumb(&mut self, orientation: Orientation, thumb_pos: usize) {
-        let lengths = self.scrollbar_thumb_lengths();
-        let available = self.available_size();
-
-        // We want self.scrollbar_thumb_offsets() to be thumb_pos
-        // steps * self.o / (self.inner + 1 - available) = thumb_pos
-        // self.o = thumb_pos * (self.inner + 1 - available) / (available + 1 - lengths)
-
-        // The new offset is:
-        // thumb_pos * (content + 1 - available) / (available + 1 - thumb size)
-        let extra =
-            (available + (1, 1)).saturating_sub(lengths).or_max((1, 1));
-
-        // We're dividing by this value, so make sure it's positive!
-        assert!(extra > Vec2::zero());
-
-        let new_offset =
-            ((self.inner_size + (1, 1)).saturating_sub(available) * thumb_pos)
-                .div_up(extra);
-        let max_offset = self.inner_size.saturating_sub(self.available_size());
-        self.offset
-            .set_axis_from(orientation, &new_offset.or_min(max_offset));
-    }
-
-    /// Computes the size we would need given the constraints.
-    ///
-    /// First be optimistic and try without scrollbars.
-    /// Then try with scrollbars if needed.
-    /// Then try again in case we now need to scroll both ways (!!!)
-    ///
-    /// Returns `(inner_size, desired_size)`
-    fn sizes(&mut self, constraint: Vec2, strict: bool) -> (Vec2, Vec2) {
-        // First: try the cache
-        let valid_cache = !self.inner.needs_relayout()
-            && self
-                .size_cache
-                .map(|cache| {
-                    cache.zip_map(constraint, SizeCache::accept).both()
-                })
-                .unwrap_or(false);
-
-        if valid_cache {
-            // eprintln!("Cache: {:?}; constraint: {:?}", self.size_cache, constraint);
-
-            // The new constraint shouldn't change much,
-            // so we can re-use previous values
-            return (
-                self.inner_size,
-                self.size_cache.unwrap().map(|c| c.value),
-            );
-        }
-
-        // Attempt 1: try without scrollbars
-        let (inner_size, size, scrollable) = self.sizes_when_scrolling(
-            constraint,
-            XY::new(false, false),
-            strict,
-        );
-
-        // If we need to add scrollbars, the available size will change.
-        if scrollable.any() && self.show_scrollbars {
-            // Attempt 2: he wants to scroll? Sure!
-            // Try again with some space for the scrollbar.
-            let (inner_size, size, new_scrollable) =
-                self.sizes_when_scrolling(constraint, scrollable, strict);
-            if scrollable == new_scrollable {
-                // Yup, scrolling did it. We're good to go now.
-                (inner_size, size)
-            } else {
-                // Again? We're now scrolling in a new direction?
-                // There is no end to this!
-                let (inner_size, size, _) = self.sizes_when_scrolling(
-                    constraint,
-                    new_scrollable,
-                    strict,
-                );
-
-                // That's enough. If the inner view changed again, ignore it!
-                // That'll teach it.
-                (inner_size, size)
-            }
-        } else {
-            // We're not showing any scrollbar, either because we don't scroll
-            // or because scrollbars are hidden.
-            (inner_size, size)
-        }
-    }
-
-    fn scrollbar_thumb_lengths(&self) -> Vec2 {
-        let available = self.available_size();
-        // The length should be (visible / total) * visible
-
-        (available * available / self.inner_size.or_max((1, 1))).or_max((1, 1))
-    }
-
-    fn scrollbar_thumb_offsets(&self, lengths: Vec2) -> Vec2 {
-        let available = self.available_size();
-        // The number of steps is 1 + the "extra space"
-        let steps = (available + (1, 1)).saturating_sub(lengths);
-        let max_offset = self.inner_size.saturating_sub(available) + (1, 1);
-
-        steps * self.offset / max_offset
-    }
-
-    /// Apply the scrolling strategy to the current scroll position.
-    fn adjust_scroll(&mut self) {
-        match self.scroll_strategy {
-            ScrollStrategy::StickToTop => self.scroll_to_top(),
-            ScrollStrategy::StickToBottom => self.scroll_to_bottom(),
-            ScrollStrategy::KeepRow => (),
-        }
+        self.core.scroll_to_right();
     }
 
     /// Returns the wrapped view.
@@ -436,259 +134,23 @@ where
     V: View,
 {
     fn draw(&self, printer: &Printer<'_, '_>) {
-        // Draw scrollbar?
-        let scrolling = self.is_scrolling();
-
-        let lengths = self.scrollbar_thumb_lengths();
-        let offsets = self.scrollbar_thumb_offsets(lengths);
-
-        let line_c = XY::new("-", "|");
-
-        let color = if printer.focused {
-            ColorStyle::highlight()
-        } else {
-            ColorStyle::highlight_inactive()
-        };
-
-        let size = self.available_size();
-
-        // Draw the scrollbars
-        XY::zip5(lengths, offsets, size, line_c, Orientation::pair()).run_if(
-            scrolling,
-            |(length, offset, size, c, orientation)| {
-                let start = printer
-                    .size
-                    .saturating_sub((1, 1))
-                    .with_axis(orientation, 0);
-                let offset = orientation.make_vec(offset, 0);
-
-                printer.print_line(orientation, start, size, c);
-
-                let thumb_c = if self
-                    .thumb_grab
-                    .map(|(o, _)| o == orientation)
-                    .unwrap_or(false)
-                {
-                    " "
-                } else {
-                    "▒"
-                };
-                printer.with_color(color, |printer| {
-                    printer.print_line(
-                        orientation,
-                        start + offset,
-                        length,
-                        thumb_c,
-                    );
-                });
-            },
-        );
-
-        // Draw the X between the two scrollbars.
-        if scrolling.both() {
-            printer.print(printer.size.saturating_sub((1, 1)), "╳");
-        }
-
-        // Draw content
-        let printer = printer
-            .cropped(size)
-            .content_offset(self.offset)
-            .inner_size(self.inner_size);
-        self.inner.draw(&printer);
+        self.core.draw(printer, &self.inner);
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {
-        // Relativize event accorging to the offset
-        let mut relative_event = event.clone();
-
-        // Should the event be treated inside, by the inner view?
-        let inside = if let Event::Mouse {
-            ref mut position,
-            ref offset,
-            ..
-        } = relative_event
-        {
-            // For mouse events, check if it falls inside the available area
-            let inside = position
-                .checked_sub(offset)
-                .map(|p| p.fits_in(self.available_size()))
-                .unwrap_or(false);
-            *position = *position + self.offset;
-            inside
-        } else {
-            // For key events, assume it's inside by default.
-            true
-        };
-
-        let result = if inside {
-            // If the event is inside, give it to the child.
-            self.inner.on_event(relative_event)
-        } else {
-            // Otherwise, pretend it wasn't there.
-            EventResult::Ignored
-        };
-
-        match result {
-            EventResult::Ignored => {
-                // If it's an arrow, try to scroll in the given direction.
-                // If it's a mouse scroll, try to scroll as well.
-                // Also allow Ctrl+arrow to move the view,
-                // but not the selection.
-                match event {
-                    Event::Mouse {
-                        event: MouseEvent::WheelUp,
-                        ..
-                    } if self.enabled.y && self.offset.y > 0 => {
-                        self.offset.y = self.offset.y.saturating_sub(3);
-                    }
-                    Event::Mouse {
-                        event: MouseEvent::WheelDown,
-                        ..
-                    } if self.enabled.y
-                        && (self.offset.y + self.available_size().y
-                            < self.inner_size.y) =>
-                    {
-                        self.offset.y = min(
-                            self.inner_size
-                                .y
-                                .saturating_sub(self.available_size().y),
-                            self.offset.y + 3,
-                        );
-                    }
-                    Event::Mouse {
-                        event: MouseEvent::Press(MouseButton::Left),
-                        position,
-                        offset,
-                    } if self.show_scrollbars
-                        && position
-                            .checked_sub(offset)
-                            .map(|position| self.start_drag(position))
-                            .unwrap_or(false) =>
-                    {
-                        // Just consume the event.
-                    }
-                    Event::Mouse {
-                        event: MouseEvent::Hold(MouseButton::Left),
-                        position,
-                        offset,
-                    } if self.show_scrollbars => {
-                        let position = position.saturating_sub(offset);
-                        self.drag(position);
-                    }
-                    Event::Mouse {
-                        event: MouseEvent::Release(MouseButton::Left),
-                        ..
-                    } => {
-                        self.release_grab();
-                    }
-                    Event::Key(Key::Home) if self.enabled.any() => {
-                        self.offset =
-                            self.enabled.select_or(Vec2::zero(), self.offset);
-                    }
-                    Event::Key(Key::End) if self.enabled.any() => {
-                        let max_offset = self
-                            .inner_size
-                            .saturating_sub(self.available_size());
-                        self.offset =
-                            self.enabled.select_or(max_offset, self.offset);
-                    }
-                    Event::Ctrl(Key::Up) | Event::Key(Key::Up)
-                        if self.enabled.y && self.offset.y > 0 =>
-                    {
-                        self.offset.y -= 1;
-                    }
-                    Event::Key(Key::PageUp)
-                        if self.enabled.y && self.offset.y > 0 =>
-                    {
-                        self.offset.y = self.offset.y.saturating_sub(5);
-                    }
-                    Event::Key(Key::PageDown)
-                        if self.enabled.y
-                            && (self.offset.y + self.available_size().y
-                                < self.inner_size.y) =>
-                    {
-                        self.offset.y += 5;
-                    }
-                    Event::Ctrl(Key::Down) | Event::Key(Key::Down)
-                        if self.enabled.y
-                            && (self.offset.y + self.available_size().y
-                                < self.inner_size.y) =>
-                    {
-                        self.offset.y += 1;
-                    }
-                    Event::Ctrl(Key::Left) | Event::Key(Key::Left)
-                        if self.enabled.x && self.offset.x > 0 =>
-                    {
-                        self.offset.x -= 1;
-                    }
-                    Event::Ctrl(Key::Right) | Event::Key(Key::Right)
-                        if self.enabled.x
-                            && (self.offset.x + self.available_size().x
-                                < self.inner_size.x) =>
-                    {
-                        self.offset.x += 1;
-                    }
-                    _ => return EventResult::Ignored,
-                };
-
-                // We just scrolled manually, so reset the scroll strategy.
-                self.scroll_strategy = ScrollStrategy::KeepRow;
-                // TODO: return callback on_scroll?
-                EventResult::Consumed(None)
-            }
-            other => {
-                // Fix offset?
-                let important = self.inner.important_area(self.inner_size);
-
-                // The furthest top-left we can go
-                let top_left = (important.bottom_right() + (1, 1))
-                    .saturating_sub(self.available_size());
-                // The furthest bottom-right we can go
-                let bottom_right = important.top_left();
-
-                // "top_left < bottom_right" is NOT guaranteed
-                // if the child is larger than the view.
-                let offset_min = Vec2::min(top_left, bottom_right);
-                let offset_max = Vec2::max(top_left, bottom_right);
-
-                self.offset =
-                    self.offset.or_max(offset_min).or_min(offset_max);
-
-                other
-            }
-        }
+        self.core.on_event(event, &mut self.inner)
     }
 
     fn layout(&mut self, size: Vec2) {
-        // Size is final now, negociations are over.
-        self.last_size = size;
-
-        // This is what we'd like
-        let (inner_size, self_size) = self.sizes(size, true);
-
-        self.inner_size = inner_size;
-
-        self.size_cache = Some(SizeCache::build(self_size, size));
-
-        self.inner.layout(self.inner_size);
-
-        // Keep the offset in the valid range.
-        self.offset = self
-            .offset
-            .or_min(self.inner_size.saturating_sub(self.available_size()));
-
-        // Possibly update the offset if we're following a specific strategy.
-        self.adjust_scroll();
+        self.core.layout(size, &mut self.inner);
     }
 
     fn needs_relayout(&self) -> bool {
-        self.inner.needs_relayout() || self.size_cache.is_none()
+        self.core.needs_relayout(|| self.inner.needs_relayout())
     }
 
     fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        let (_, size) = self.sizes(constraint, false);
-
-        size
+        self.core.required_size(constraint, &mut self.inner)
     }
 
     fn call_on_any<'a>(&mut self, selector: &Selector<'_>, cb: AnyCb<'a>) {
@@ -700,7 +162,8 @@ where
     }
 
     fn take_focus(&mut self, source: Direction) -> bool {
-        let is_scrollable = self.is_scrolling().any();
-        self.inner.take_focus(source) || is_scrollable
+        let inner = &mut self.inner;
+        self.core
+            .take_focus(source, |source| inner.take_focus(source))
     }
 }