Refactor scroll::Core mechanism.

Moved most View-trait-performing-functions outside of `scroll::Core`
into `scroll::raw`.
Added a `Scroller` trait and convenience methods like `scroll::layout` to
weave the borrows appropriately.

src/lib.rs

@@ -87,7 +87,6 @@ pub mod align;
 pub mod direction;
 pub mod logger;
 pub mod menu;
-pub mod rect;
 pub mod theme;
 pub mod vec;
 pub mod views;
@@ -95,6 +94,7 @@ pub mod views;
 // This probably doesn't need to be public?
 mod cursive;
 mod printer;
+mod rect;
 mod with;
 mod xy;
 
@@ -103,8 +103,9 @@ mod utf8;
 
 pub mod backend;
 
-pub use crate::cursive::{CbFunc, CbSink, Cursive, ScreenId};
+pub use self::cursive::{CbFunc, CbSink, Cursive, ScreenId};
-pub use crate::printer::Printer;
+pub use self::printer::Printer;
-pub use crate::vec::Vec2;
+pub use self::rect::Rect;
-pub use crate::with::With;
+pub use self::vec::Vec2;
-pub use crate::xy::XY;
+pub use self::with::With;
+pub use self::xy::XY;

src/view/scroll/base.rs

@@ -1,131 +0,0 @@
-use crate::vec::Vec2;
-use crate::Printer;
-
-use crate::direction::Direction;
-use crate::event::{Event, EventResult};
-use crate::view::scroll::ScrollCore;
-use crate::view::scroll::{InnerLayout, InnerOnEvent, InnerRequiredSize};
-
-/// 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 {
-    core: ScrollCore,
-}
-
-struct RequiredSize<F>(F);
-
-impl<F> InnerRequiredSize for RequiredSize<F>
-where
-    F: FnMut(Vec2) -> Vec2,
-{
-    fn needs_relayout(&self) -> bool {
-        true
-    }
-
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        self.0(constraint)
-    }
-}
-
-impl<F> InnerLayout for RequiredSize<F>
-where
-    F: FnMut(Vec2) -> Vec2,
-{
-    fn layout(&mut self, _size: Vec2) {}
-
-    fn needs_relayout(&self) -> bool {
-        true
-    }
-
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        self.0(constraint)
-    }
-}
-
-impl ScrollBase {
-    /// Creates a new, uninitialized scrollbar.
-    pub fn new() -> Self {
-        ScrollBase {
-            core: ScrollCore::new(),
-        }
-    }
-
-    /// Performs `View::layout()`.
-    pub fn layout<F>(&mut self, size: Vec2, required_size: F)
-    where
-        F: FnMut(Vec2) -> Vec2,
-    {
-        self.core.layout(size, RequiredSize(required_size));
-    }
-
-    /// Performs `View::required_size()`.
-    pub fn required_size<F>(
-        &mut self, constraint: Vec2, required_size: F,
-    ) -> Vec2
-    where
-        F: FnMut(Vec2) -> Vec2,
-    {
-        self.core
-            .required_size(constraint, RequiredSize(required_size))
-    }
-
-    /// 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<'_, '_>, mut line_drawer: F)
-    where
-        F: FnMut(&Printer<'_, '_>, usize),
-    {
-        self.core.draw(printer, |printer| {
-            let start = printer.content_offset.y;
-            let end = start + printer.output_size.y;
-            for y in start..end {
-                let printer =
-                    printer.offset((0, y)).cropped((printer.size.x, 1));
-                line_drawer(&printer, y);
-            }
-        });
-    }
-
-    /// Performs `View::take_focus()`.
-    pub fn take_focus<F>(
-        &mut self, source: Direction, inner_take_focus: F,
-    ) -> bool
-    where
-        F: FnOnce(Direction) -> bool,
-    {
-        self.core.take_focus(source, inner_take_focus)
-    }
-
-    /// Performs `View::on_event()`.
-    pub fn on_event<I>(&mut self, event: Event, inner: I) -> EventResult
-    where
-        I: InnerOnEvent,
-    {
-        self.core.on_event(event, inner)
-    }
-}

src/view/scroll/core.rs

@@ -1,6 +1,6 @@
 use std::cmp::min;
 
-use crate::direction::{Direction, Orientation};
+use crate::direction::Orientation;
 use crate::event::{AnyCb, Event, EventResult, Key, MouseButton, MouseEvent};
 use crate::printer::Printer;
 use crate::rect::Rect;
@@ -10,13 +10,25 @@ use crate::view::{ScrollStrategy, Selector, SizeCache};
 use crate::with::With;
 use crate::XY;
 
-use crate::view::scroll::{InnerLayout, InnerOnEvent, InnerRequiredSize};
+/// Describes an item with a scroll core.
+///
+/// This trait is used to represent "something that can scroll".
+/// All it needs is an accessible core.
+///
+/// See the various methods in the [`scroll`](crate::view::scroll) module.
+pub trait Scroller {
+    /// Returns a mutable access to the scroll core.
+    fn get_scroller_mut(&mut self) -> &mut Core;
+
+    /// Returns an immutable access to the scroll core.
+    fn get_scroller(&self) -> &Core;
+}
 
 /// Core system for scrolling views.
 ///
 /// See also [`ScrollView`](crate::views::ScrollView).
 #[derive(Debug)]
-pub struct ScrollCore {
+pub struct Core {
     /// This is the size the child thinks we're giving him.
     inner_size: Vec2,
 
@@ -57,16 +69,16 @@ pub struct ScrollCore {
     scroll_strategy: ScrollStrategy,
 }
 
-impl Default for ScrollCore {
+impl Default for Core {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl ScrollCore {
+impl Core {
-    /// Creates a new `ScrollCore`.
+    /// Creates a new `Core`.
     pub fn new() -> Self {
-        ScrollCore {
+        Core {
             inner_size: Vec2::zero(),
             offset: Vec2::zero(),
             last_size: Vec2::zero(),
@@ -79,11 +91,10 @@ impl ScrollCore {
         }
     }
 
-    /// Performs the `View::draw()` operation.
+    /// Returns a sub-printer ready to draw the content.
-    pub fn draw<F>(&self, printer: &Printer<'_, '_>, inner_draw: F)
+    pub fn sub_printer<'a, 'b>(
-    where
+        &self, printer: &Printer<'a, 'b>,
-        F: FnOnce(&Printer<'_, '_>),
+    ) -> Printer<'a, 'b> {
-    {
         // Draw scrollbar?
         let scrolling = self.is_scrolling();
 
@@ -138,27 +149,21 @@ impl ScrollCore {
         }
 
         // Draw content
-        let printer = printer
+        printer
             .cropped(size)
             .content_offset(self.offset)
-            .inner_size(self.inner_size);
+            .inner_size(self.inner_size)
-
-        inner_draw(&printer);
     }
 
-    /// Performs `View::on_event()`
+    /// Returns `true` if `event` should be processed by the content.
-    pub fn on_event<I: InnerOnEvent>(
+    ///
-        &mut self, event: Event, mut inner: I,
+    /// This also updates `event` so that it is relative to the content.
-    ) -> EventResult {
+    pub fn is_event_inside(&self, event: &mut Event) -> bool {
-        // Relativize event accorging to the offset
+        if let Event::Mouse {
-        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
+        } = event
         {
             // For mouse events, check if it falls inside the available area
             let inside = position
@@ -170,17 +175,15 @@ impl ScrollCore {
         } else {
             // For key events, assume it's inside by default.
             true
-        };
+        }
+    }
 
-        let result = if inside {
+    /// Handle an event after processing by the content.
-            // If the event is inside, give it to the child.
+    pub fn on_inner_event(
-            inner.on_event(relative_event)
+        &mut self, event: Event, inner_result: EventResult,
-        } else {
+        important_area: Rect,
-            // Otherwise, pretend it wasn't there.
+    ) -> EventResult {
-            EventResult::Ignored
+        match inner_result {
-        };
-
-        match result {
             EventResult::Ignored => {
                 // The view ignored the event, so we're free to use it.
 
@@ -294,7 +297,7 @@ impl ScrollCore {
                 // The view consumed the event. Maybe something changed?
 
                 // Fix offset?
-                let important = inner.important_area(self.inner_size);
+                let important = important_area;
 
                 // The furthest top-left we can go
                 let top_left = (important.bottom_right() + (1, 1))
@@ -315,21 +318,28 @@ impl ScrollCore {
         }
     }
 
-    /// Performs `View::layout()`
+    /// Specifies the size given in a layout phase.
-    pub fn layout<I: InnerLayout>(&mut self, size: Vec2, mut inner: I) {
+    pub(crate) fn set_last_size(&mut self, last_size: Vec2) {
-        // Size is final now, negociations are over.
+        self.last_size = last_size;
-        self.last_size = size;
+    }
 
-        // This is what we'd like
+    /// Returns the size last given in `set_last_size()`.
-        let (inner_size, self_size) =
+    pub fn last_size(&self) -> Vec2 {
-            self.sizes(size, true, Layout2Sizes { inner: &mut inner });
+        self.last_size
+    }
 
+    /// Specifies the size allocated to the content.
+    pub(crate) fn set_inner_size(&mut self, inner_size: Vec2) {
         self.inner_size = inner_size;
+    }
 
-        self.size_cache = Some(SizeCache::build(self_size, size));
+    /// Rebuild the cache with the given parameters.
-
+    pub(crate) fn build_cache(&mut self, self_size: Vec2, last_size: Vec2) {
-        inner.layout(self.inner_size);
+        self.size_cache = Some(SizeCache::build(self_size, last_size));
+    }
 
+    /// Makes sure the viewport is within the content.
+    pub(crate) fn update_offset(&mut self) {
         // Keep the offset in the valid range.
         self.offset = self
             .offset
@@ -339,25 +349,11 @@ impl ScrollCore {
         self.adjust_scroll();
     }
 
-    /// Performs `View::needs_relayout()`
+    /// Returns `true` if we should relayout, no matter the content.
-    pub fn needs_relayout<F>(&self, inner_needs_relayout: F) -> bool
+    ///
-    where
+    /// Even if this returns `false`, the content itself might still needs to relayout.
-        F: FnOnce() -> bool,
+    pub fn needs_relayout(&self) -> bool {
-    {
+        self.size_cache.is_none()
-        self.size_cache.is_none() || inner_needs_relayout()
-    }
-
-    /// Performs `View::required_size()`
-    pub fn required_size<I: InnerRequiredSize>(
-        &mut self, constraint: Vec2, mut inner: I,
-    ) -> Vec2 {
-        let (_, size) = self.sizes(
-            constraint,
-            false,
-            Required2Sizes { inner: &mut inner },
-        );
-
-        size
     }
 
     /// Performs `View::call_on_any()`
@@ -380,17 +376,6 @@ impl ScrollCore {
         inner_focus_view(selector)
     }
 
-    /// Performs `View::take_focus()`
-    pub fn take_focus<F>(
-        &mut self, source: Direction, inner_take_focus: F,
-    ) -> bool
-    where
-        F: FnOnce(Direction) -> bool,
-    {
-        let is_scrollable = self.is_scrolling().any();
-        inner_take_focus(source) || is_scrollable
-    }
-
     /// Returns the viewport in the inner content.
     pub fn content_viewport(&self) -> Rect {
         Rect::from_size(self.offset, self.available_size())
@@ -431,6 +416,19 @@ impl ScrollCore {
         self.with(|s| s.set_scrollbar_padding(scrollbar_padding))
     }
 
+    /// Returns the padding between content and scrollbar.
+    pub fn get_scrollbar_padding(&self) -> Vec2 {
+        self.scrollbar_padding
+    }
+
+    /// For each axis, returns `true` if this view can scroll.
+    ///
+    /// For example, a vertically-scrolling view will return
+    /// `XY { x: false, y: true }`.
+    pub fn is_enabled(&self) -> XY<bool> {
+        self.enabled
+    }
+
     /// Control whether scroll bars are visibile.
     ///
     /// Defaults to `true`.
@@ -445,6 +443,18 @@ impl ScrollCore {
         self.with(|s| s.set_show_scrollbars(show_scrollbars))
     }
 
+    /// Returns `true` if we will show scrollbars when needed.
+    ///
+    /// Scrollbars are always hidden when not needed.
+    pub fn get_show_scrollbars(&self) -> bool {
+        self.show_scrollbars
+    }
+
+    /// Returns the size given to the content on the last layout phase.
+    pub fn inner_size(&self) -> Vec2 {
+        self.inner_size
+    }
+
     /// Sets the scroll offset to the given value
     pub fn set_offset<S>(&mut self, offset: S)
     where
@@ -529,7 +539,7 @@ impl ScrollCore {
     }
 
     /// Returns for each axis if we are scrolling.
-    fn is_scrolling(&self) -> XY<bool> {
+    pub fn is_scrolling(&self) -> XY<bool> {
         self.inner_size.zip_map(self.last_size, |i, s| i > s)
     }
 
@@ -543,7 +553,7 @@ impl ScrollCore {
     /// 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 {
+    pub fn scrollbar_size(&self) -> Vec2 {
         self.is_scrolling()
             .swap()
             .select_or(self.scrollbar_padding + (1, 1), Vec2::zero())
@@ -558,49 +568,6 @@ impl ScrollCore {
         }
     }
 
-    /// Compute the size we would need.
-    ///
-    /// Given the constraints, and the axis that need scrollbars.
-    ///
-    /// Returns `(inner_size, size, scrollable)`.
-    fn sizes_when_scrolling<I: InnerSizes>(
-        &mut self, constraint: Vec2, scrollable: XY<bool>, strict: bool,
-        inner: &mut I,
-    ) -> (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 = 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.
@@ -679,74 +646,17 @@ impl ScrollCore {
             .set_axis_from(orientation, &new_offset.or_min(max_offset));
     }
 
-    /// Computes the size we would need given the constraints.
+    /// Tries to apply the cache to the current constraint.
     ///
-    /// First be optimistic and try without scrollbars.
+    /// Returns the cached value if it works, or `None`.
-    /// Then try with scrollbars if needed.
+    pub(crate) fn try_cache(&self, constraint: Vec2) -> Option<(Vec2, Vec2)> {
-    /// Then try again in case we now need to scroll both ways (!!!)
+        self.size_cache.and_then(|cache| {
-    ///
+            if cache.zip_map(constraint, SizeCache::accept).both() {
-    /// Returns `(inner_size, desired_size)`
+                Some((self.inner_size, cache.map(|c| c.value)))
-    fn sizes<I: InnerSizes>(
-        &mut self, constraint: Vec2, strict: bool, mut inner: I,
-    ) -> (Vec2, Vec2) {
-        // First: try the cache
-        let valid_cache = !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,
-            &mut inner,
-        );
-
-        // 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, &mut inner,
-                );
-            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?
+                None
-                // There is no end to this!
-                let (inner_size, size, _) = self.sizes_when_scrolling(
-                    constraint,
-                    new_scrollable,
-                    strict,
-                    &mut inner,
-                );
-
-                // 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 {
@@ -774,34 +684,3 @@ impl ScrollCore {
         }
     }
 }
-
-struct Layout2Sizes<'a, I> {
-    inner: &'a mut I,
-}
-
-trait InnerSizes {
-    fn needs_relayout(&self) -> bool;
-    fn required_size(&mut self, constraint: Vec2) -> Vec2;
-}
-
-impl<'a, I: InnerLayout> InnerSizes for Layout2Sizes<'a, I> {
-    fn needs_relayout(&self) -> bool {
-        self.inner.needs_relayout()
-    }
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        self.inner.required_size(constraint)
-    }
-}
-
-struct Required2Sizes<'a, I> {
-    inner: &'a mut I,
-}
-
-impl<'a, I: InnerRequiredSize> InnerSizes for Required2Sizes<'a, I> {
-    fn needs_relayout(&self) -> bool {
-        self.inner.needs_relayout()
-    }
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        self.inner.required_size(constraint)
-    }
-}

src/view/scroll/mod.rs

@@ -2,17 +2,17 @@
 //!
 //! *This module is still unstable and may go through breaking changes.*
 //!
-//! This module defines [`ScrollCore`](crate::view::scroll::ScrollCore) and related traits.
+//! This module defines [`Core`](crate::view::scroll::Core) and related traits.
 //!
 //! [`ScrollView`](crate::views::ScrollView) may be an easier way to add scrolling to an existing view.
 
-mod base;
 mod core;
-mod traits;
+mod raw;
 
-pub use self::base::ScrollBase;
+pub use self::core::{Core, Scroller};
-pub use self::core::ScrollCore;
+
-pub use self::traits::{InnerLayout, InnerOnEvent, InnerRequiredSize};
+use crate::event::{Event, EventResult};
+use crate::{Printer, Rect, Vec2};
 
 /// Defines the scrolling behaviour on content or size change
 #[derive(Debug)]
@@ -30,3 +30,210 @@ impl Default for ScrollStrategy {
         ScrollStrategy::KeepRow
     }
 }
+
+/// Performs `View::on_event` on a `scroll::Scroller`.
+///
+/// Example:
+///
+/// ```rust,ignore
+/// fn on_event(&mut self, event: Event) -> EventResult {
+///     scroll::on_event(self, event, Self::inner_on_event, Self::inner_important_area)
+/// }
+/// ```
+pub fn on_event<T, OnEvent, ImportantArea>(
+    scroller: &mut T, event: Event, on_event: OnEvent,
+    important_area: ImportantArea,
+) -> EventResult
+where
+    T: Scroller,
+    OnEvent: FnMut(&mut T, Event) -> EventResult,
+    ImportantArea: FnMut(&T, Vec2) -> Rect,
+{
+    raw::on_event(
+        event,
+        scroller,
+        Scroller::get_scroller_mut,
+        on_event,
+        important_area,
+    )
+}
+
+/// Performs `View::important_area` on a `scroll::Scroller`.
+pub fn important_area<T, ImportantArea>(
+    scroller: &T, size: Vec2, mut important_area: ImportantArea,
+) -> Rect
+where
+    T: Scroller,
+    ImportantArea: FnMut(&T, Vec2) -> Rect,
+{
+    let viewport = scroller.get_scroller().content_viewport();
+    let area = important_area(scroller, size);
+    let top_left = area.top_left().saturating_sub(viewport.top_left());
+    let bot_right = area
+        .bottom_right()
+        .saturating_sub(viewport.top_left())
+        .or_min(viewport.bottom_right());
+
+    Rect::from_corners(top_left, bot_right)
+}
+
+/// Performs `View::layout` on a `scroll::Scroller`.
+pub fn layout<T, Layout, RequiredSize>(
+    scroller: &mut T, size: Vec2, needs_relayout: bool, layout: Layout,
+    required_size: RequiredSize,
+) where
+    T: Scroller,
+    Layout: FnMut(&mut T, Vec2),
+    RequiredSize: FnMut(&mut T, Vec2) -> Vec2,
+{
+    raw::layout(
+        size,
+        needs_relayout,
+        scroller,
+        Scroller::get_scroller_mut,
+        required_size,
+        layout,
+    );
+}
+
+/// Performs `View::required_size` on a `scroll::Scroller`.
+pub fn required_size<T, RequiredSize>(
+    scroller: &mut T, size: Vec2, needs_relayout: bool,
+    required_size: RequiredSize,
+) -> Vec2
+where
+    T: Scroller,
+    RequiredSize: FnMut(&mut T, Vec2) -> Vec2,
+{
+    raw::required_size(
+        size,
+        needs_relayout,
+        scroller,
+        Scroller::get_scroller_mut,
+        required_size,
+    )
+}
+
+/// Performs `View::draw` on a `scroll::Scroller`.
+pub fn draw<T, Draw>(scroller: &T, printer: &Printer, draw: Draw)
+where
+    T: Scroller,
+    Draw: FnOnce(&T, &Printer),
+{
+    raw::draw(printer, scroller, Scroller::get_scroller, draw);
+}
+
+/// Performs a line-based `View::draw` on a `scroll::Scroller`.
+///
+/// This is an alternative to `scroll::draw()` when you just need to print individual lines.
+pub fn draw_lines<T, LineDrawer>(
+    scroller: &T, printer: &Printer, mut line_drawer: LineDrawer,
+) where
+    T: Scroller,
+    LineDrawer: FnMut(&T, &Printer, usize),
+{
+    draw(scroller, printer, |s, printer| {
+        let start = printer.content_offset.y;
+        let end = start + printer.output_size.y;
+        for y in start..end {
+            let printer = printer.offset((0, y)).cropped((printer.size.x, 1));
+            line_drawer(s, &printer, y);
+        }
+    });
+}
+
+/// Draws a frame around the scrollable content.
+///
+/// `left_border` will be called for each row to draw the left border for the given line number.
+pub fn draw_frame<T, LeftBorder, TopBorder, RightBorder, BottomBorder>(
+    scroller: &T, printer: &Printer, mut left_border: LeftBorder,
+    mut top_border: TopBorder, mut right_border: RightBorder,
+    mut bottom_border: BottomBorder,
+) where
+    T: Scroller,
+    LeftBorder: FnMut(&T, &Printer, usize),
+    TopBorder: FnMut(&T, &Printer, usize),
+    RightBorder: FnMut(&T, &Printer, usize),
+    BottomBorder: FnMut(&T, &Printer, usize),
+{
+    let viewport = scroller.get_scroller().content_viewport();
+    let size = printer.size.saturating_sub((1, 1));
+
+    for (i, x) in (viewport.left()..=viewport.right()).enumerate() {
+        top_border(scroller, &printer.offset((i + 1, 0)), x);
+        bottom_border(scroller, &printer.offset((i + 1, size.y)), x);
+    }
+
+    // Also draw padding
+    let scrollbar_size = scroller.get_scroller().scrollbar_size();
+    printer.print_hline((viewport.right() + 2, 0), scrollbar_size.x, "─");
+    printer.print_hline(
+        (viewport.right() + 2, size.y),
+        scrollbar_size.x,
+        "─",
+    );
+    printer.print_vline((0, viewport.bottom() + 2), scrollbar_size.y, "│");
+    printer.print_vline(
+        (size.x, viewport.bottom() + 2),
+        scrollbar_size.y,
+        "│",
+    );
+
+    for (i, y) in (viewport.top()..=viewport.bottom()).enumerate() {
+        left_border(scroller, &printer.offset((0, i + 1)), y);
+        right_border(scroller, &printer.offset((size.x, i + 1)), y);
+    }
+
+    printer.print((0, 0), "┌");
+    printer.print(size.keep_y(), "└");
+    printer.print(size.keep_x(), "┐");
+    printer.print(size, "┘");
+}
+
+/// Draws a box-style frame around a scrollable content.
+///
+/// Assumes horizontal lines are present in the content whenever `is_h_delim`
+/// returns `true` (and vertical lines when `is_v_delim` returns `true`).
+///
+/// It will print a box with the appropriate `├`, `┤` and so on.
+pub fn draw_box_frame<T, IsHDelim, IsVDelim>(
+    scroller: &T, printer: &Printer, is_h_delim: IsHDelim,
+    is_v_delim: IsVDelim,
+) where
+    T: Scroller,
+    IsHDelim: Fn(&T, usize) -> bool,
+    IsVDelim: Fn(&T, usize) -> bool,
+{
+    draw_frame(
+        scroller,
+        printer,
+        |s, printer, y| {
+            if is_h_delim(s, y) {
+                printer.print((0, 0), "├");
+            } else {
+                printer.print((0, 0), "│");
+            }
+        },
+        |s, printer, x| {
+            if is_v_delim(s, x) {
+                printer.print((0, 0), "┬");
+            } else {
+                printer.print((0, 0), "─");
+            }
+        },
+        |s, printer, y| {
+            if is_h_delim(s, y) {
+                printer.print((0, 0), "┤");
+            } else {
+                printer.print((0, 0), "│");
+            }
+        },
+        |s, printer, x| {
+            if is_v_delim(s, x) {
+                printer.print((0, 0), "┴");
+            } else {
+                printer.print((0, 0), "─");
+            }
+        },
+    );
+}

src/view/scroll/raw.rs

@@ -0,0 +1,198 @@
+use crate::event::{Event, EventResult};
+use crate::rect::Rect;
+use crate::view::scroll;
+use crate::xy::XY;
+use crate::Printer;
+use crate::Vec2;
+
+pub fn draw<Model, GetScroller, Draw>(
+    printer: &Printer, model: &Model, mut get_scroller: GetScroller,
+    inner_draw: Draw,
+) where
+    Model: ?Sized,
+    GetScroller: FnMut(&Model) -> &scroll::Core,
+    Draw: FnOnce(&Model, &Printer),
+{
+    let printer = get_scroller(model).sub_printer(printer);
+    inner_draw(model, &printer);
+}
+
+fn sizes_when_scrolling<Model, GetScroller, RequiredSize>(
+    constraint: Vec2, scrollable: XY<bool>, strict: bool, model: &mut Model,
+    get_scroller: &mut GetScroller, required_size: &mut RequiredSize,
+) -> (Vec2, Vec2, XY<bool>)
+where
+    Model: ?Sized,
+    GetScroller: FnMut(&mut Model) -> &mut scroll::Core,
+    RequiredSize: FnMut(&mut Model, Vec2) -> Vec2,
+{
+    // This is the size taken by the scrollbars.
+    let scrollbar_size = scrollable.swap().select_or(
+        get_scroller(model).get_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 = required_size(model, available);
+
+    // Where we're "enabled", accept the constraints.
+    // Where we're not, just forward inner_size.
+    let size = get_scroller(model).is_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 = get_scroller(model)
+        .is_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)
+}
+
+fn sizes<Model, GetScroller, RequiredSize>(
+    constraint: Vec2, strict: bool, needs_relayout: bool, model: &mut Model,
+    get_scroller: &mut GetScroller, required_size: &mut RequiredSize,
+) -> (Vec2, Vec2)
+where
+    Model: ?Sized,
+    GetScroller: FnMut(&mut Model) -> &mut scroll::Core,
+    RequiredSize: FnMut(&mut Model, Vec2) -> Vec2,
+{
+    if !needs_relayout {
+        if let Some(cached) = get_scroller(model).try_cache(constraint) {
+            return cached;
+        }
+    }
+
+    // Attempt 1: try without scrollbars
+    let (inner_size, size, scrollable) = sizes_when_scrolling(
+        constraint,
+        XY::new(false, false),
+        strict,
+        model,
+        get_scroller,
+        required_size,
+    );
+
+    // If we need to add scrollbars, the available size will change.
+    if scrollable.any() && get_scroller(model).get_show_scrollbars() {
+        // Attempt 2: he wants to scroll? Sure!
+        // Try again with some space for the scrollbar.
+        let (inner_size, size, new_scrollable) = sizes_when_scrolling(
+            constraint,
+            scrollable,
+            strict,
+            model,
+            get_scroller,
+            required_size,
+        );
+        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, _) = sizes_when_scrolling(
+                constraint,
+                new_scrollable,
+                strict,
+                model,
+                get_scroller,
+                required_size,
+            );
+
+            // 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)
+    }
+}
+
+pub fn layout<Model, GetScroller, RequiredSize, Layout>(
+    size: Vec2, needs_relayout: bool, model: &mut Model,
+    mut get_scroller: GetScroller, mut required_size: RequiredSize,
+    mut layout: Layout,
+) where
+    Model: ?Sized,
+    GetScroller: FnMut(&mut Model) -> &mut scroll::Core,
+    RequiredSize: FnMut(&mut Model, Vec2) -> Vec2,
+    Layout: FnMut(&mut Model, Vec2),
+{
+    get_scroller(model).set_last_size(size);
+
+    // This is what we'd like
+    let (inner_size, self_size) = sizes(
+        size,
+        true,
+        needs_relayout,
+        model,
+        &mut get_scroller,
+        &mut required_size,
+    );
+
+    get_scroller(model).set_inner_size(inner_size);
+    get_scroller(model).build_cache(self_size, size);
+
+    layout(model, inner_size);
+
+    get_scroller(model).update_offset();
+}
+
+pub fn required_size<Model, GetScroller, RequiredSize>(
+    constraint: Vec2, needs_relayout: bool, model: &mut Model,
+    mut get_scroller: GetScroller, mut required_size: RequiredSize,
+) -> Vec2
+where
+    Model: ?Sized,
+    GetScroller: FnMut(&mut Model) -> &mut scroll::Core,
+    RequiredSize: FnMut(&mut Model, Vec2) -> Vec2,
+{
+    let (_, size) = sizes(
+        constraint,
+        false,
+        needs_relayout,
+        model,
+        &mut get_scroller,
+        &mut required_size,
+    );
+
+    size
+}
+
+pub fn on_event<Model, GetScroller, OnEvent, ImportantArea>(
+    event: Event, model: &mut Model, mut get_scroller: GetScroller,
+    mut on_event: OnEvent, mut important_area: ImportantArea,
+) -> EventResult
+where
+    Model: ?Sized,
+    GetScroller: FnMut(&mut Model) -> &mut scroll::Core,
+    OnEvent: FnMut(&mut Model, Event) -> EventResult,
+    ImportantArea: FnMut(&Model, Vec2) -> Rect,
+{
+    let mut relative_event = event.clone();
+    let inside = get_scroller(model).is_event_inside(&mut relative_event);
+    let result = if inside {
+        on_event(model, relative_event)
+    } else {
+        EventResult::Ignored
+    };
+    let inner_size = get_scroller(model).inner_size();
+    let important = important_area(model, inner_size);
+    get_scroller(model).on_inner_event(event, result, important)
+}

src/view/scroll/traits.rs

@@ -1,63 +0,0 @@
-use crate::event::{Event, EventResult};
-use crate::rect::Rect;
-
-use crate::vec::Vec2;
-use crate::view::View;
-
-/// Inner implementation for `ScrollCore::on_event`
-pub trait InnerOnEvent {
-    /// Performs `View::on_event()`
-    fn on_event(&mut self, event: Event) -> EventResult;
-
-    /// Performs `View::important_area()`
-    fn important_area(&self, size: Vec2) -> Rect;
-}
-
-impl<'a, V: View> InnerOnEvent for &'a mut V {
-    fn on_event(&mut self, event: Event) -> EventResult {
-        <V as View>::on_event(self, event)
-    }
-    fn important_area(&self, size: Vec2) -> Rect {
-        <V as View>::important_area(self, size)
-    }
-}
-
-/// Inner implementation for `ScrollCore::draw()`
-/// Inner implementation for `ScrollCore::InnerLayout()`
-pub trait InnerLayout {
-    /// Performs `View::layout()`
-    fn layout(&mut self, size: Vec2);
-    /// Performs `View::needs_relayout()`
-    fn needs_relayout(&self) -> bool;
-    /// Performs `View::required_size()`
-    fn required_size(&mut self, constraint: Vec2) -> Vec2;
-}
-
-impl<'a, V: View> InnerLayout for &'a mut V {
-    fn layout(&mut self, size: Vec2) {
-        <V as View>::layout(self, size);
-    }
-    fn needs_relayout(&self) -> bool {
-        <V as View>::needs_relayout(self)
-    }
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        <V as View>::required_size(self, constraint)
-    }
-}
-
-/// Inner implementation for `ScrollCore::required_size()`
-pub trait InnerRequiredSize {
-    /// Performs `View::needs_relayout()`
-    fn needs_relayout(&self) -> bool;
-    /// Performs `View::required_size()`
-    fn required_size(&mut self, constraint: Vec2) -> Vec2;
-}
-
-impl<V: View> InnerRequiredSize for &mut V {
-    fn needs_relayout(&self) -> bool {
-        <V as View>::needs_relayout(self)
-    }
-    fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        <V as View>::required_size(self, constraint)
-    }
-}

src/views/menu_popup.rs

@@ -5,7 +5,7 @@ use crate::event::{
 use crate::menu::{MenuItem, MenuTree};
 use crate::rect::Rect;
 use crate::vec::Vec2;
-use crate::view::scroll::{InnerOnEvent, ScrollBase};
+use crate::view::scroll;
 use crate::view::{Position, View};
 use crate::views::OnEventView;
 use crate::Cursive;
@@ -19,11 +19,23 @@ use unicode_width::UnicodeWidthStr;
 pub struct MenuPopup {
     menu: Rc<MenuTree>,
     focus: usize,
-    scrollbase: ScrollBase,
+    scroll_core: scroll::Core,
     align: Align,
     on_dismiss: Option<Callback>,
     on_action: Option<Callback>,
-    last_size: Vec2,
+}
+
+// The `scroll::Scroller` trait is used to weave the borrow phases.
+//
+// TODO: use some macro to auto-generate this.
+impl scroll::Scroller for MenuPopup {
+    fn get_scroller(&self) -> &scroll::Core {
+        &self.scroll_core
+    }
+
+    fn get_scroller_mut(&mut self) -> &mut scroll::Core {
+        &mut self.scroll_core
+    }
 }
 
 impl MenuPopup {
@@ -32,11 +44,10 @@ impl MenuPopup {
         MenuPopup {
             menu,
             focus: 0,
-            scrollbase: ScrollBase::new(),
+            scroll_core: scroll::Core::new(),
             align: Align::top_left(),
             on_dismiss: None,
             on_action: None,
-            last_size: Vec2::zero(),
         }
     }
 
@@ -52,6 +63,11 @@ impl MenuPopup {
         self.with(|s| s.set_focus(focus))
     }
 
+    /// Returns the position of the currently focused child.
+    pub fn get_focus(&self) -> usize {
+        self.focus
+    }
+
     fn item_width(item: &MenuItem) -> usize {
         match *item {
             MenuItem::Delimiter => 1,
@@ -107,6 +123,193 @@ impl MenuPopup {
     pub fn set_on_action<F: 'static + Fn(&mut Cursive)>(&mut self, f: F) {
         self.on_action = Some(Callback::from_fn(f));
     }
+
+    fn scroll_up(&mut self, mut n: usize, cycle: bool) {
+        while n > 0 {
+            if self.focus > 0 {
+                self.focus -= 1;
+            } else if cycle {
+                self.focus = self.menu.children.len() - 1;
+            } else {
+                break;
+            }
+
+            if !self.menu.children[self.focus].is_delimiter() {
+                n -= 1;
+            }
+        }
+    }
+
+    fn scroll_down(&mut self, mut n: usize, cycle: bool) {
+        while n > 0 {
+            if self.focus + 1 < self.menu.children.len() {
+                self.focus += 1;
+            } else if cycle {
+                self.focus = 0;
+            } else {
+                // Stop if we're at the bottom.
+                break;
+            }
+
+            if !self.menu.children[self.focus].is_delimiter() {
+                n -= 1;
+            }
+        }
+    }
+
+    fn submit(&mut self) -> EventResult {
+        match self.menu.children[self.focus] {
+            MenuItem::Leaf(_, ref cb) => {
+                let cb = cb.clone();
+                let action_cb = self.on_action.clone();
+                EventResult::with_cb(move |s| {
+                    // Remove ourselves from the face of the earth
+                    s.pop_layer();
+                    // If we had prior orders, do it now.
+                    if let Some(ref action_cb) = action_cb {
+                        action_cb.clone()(s);
+                    }
+                    // And transmit his last words.
+                    cb.clone()(s);
+                })
+            }
+            MenuItem::Subtree(_, ref tree) => self.make_subtree_cb(tree),
+            _ => unreachable!("Delimiters cannot be submitted."),
+        }
+    }
+
+    fn dismiss(&mut self) -> EventResult {
+        let dismiss_cb = self.on_dismiss.clone();
+        EventResult::with_cb(move |s| {
+            if let Some(ref cb) = dismiss_cb {
+                cb.clone()(s);
+            }
+            s.pop_layer();
+        })
+    }
+
+    fn make_subtree_cb(&self, tree: &Rc<MenuTree>) -> EventResult {
+        let tree = Rc::clone(tree);
+        let max_width = 4 + self
+            .menu
+            .children
+            .iter()
+            .map(MenuPopup::item_width)
+            .max()
+            .unwrap_or(1);
+        let offset = Vec2::new(max_width, self.focus);
+        let action_cb = self.on_action.clone();
+
+        EventResult::with_cb(move |s| {
+            let action_cb = action_cb.clone();
+            s.screen_mut().add_layer_at(
+                Position::parent(offset),
+                OnEventView::new(MenuPopup::new(Rc::clone(&tree)).on_action(
+                    move |s| {
+                        // This will happen when the subtree popup
+                        // activates something;
+                        // First, remove ourselve.
+                        s.pop_layer();
+                        if let Some(ref action_cb) = action_cb {
+                            action_cb.clone()(s);
+                        }
+                    },
+                ))
+                .on_event(Key::Left, |s| {
+                    s.pop_layer();
+                }),
+            );
+        })
+    }
+
+    /// Handle an event for the content.
+    ///
+    /// Here the event has already been relativized. This means `y=0` points to the first item.
+    fn inner_on_event(&mut self, event: Event) -> EventResult {
+        match event {
+            Event::Key(Key::Up) => self.scroll_up(1, true),
+            Event::Key(Key::PageUp) => self.scroll_up(5, false),
+            Event::Key(Key::Down) => self.scroll_down(1, true),
+            Event::Key(Key::PageDown) => self.scroll_down(5, false),
+
+            Event::Key(Key::Home) => self.focus = 0,
+            Event::Key(Key::End) => {
+                self.focus = self.menu.children.len().saturating_sub(1)
+            }
+
+            Event::Key(Key::Right)
+                if self.menu.children[self.focus].is_subtree() =>
+            {
+                return match self.menu.children[self.focus] {
+                    MenuItem::Subtree(_, ref tree) => {
+                        self.make_subtree_cb(tree)
+                    }
+                    _ => unreachable!("Child is a subtree"),
+                };
+            }
+            Event::Key(Key::Enter)
+                if !self.menu.children[self.focus].is_delimiter() =>
+            {
+                return self.submit();
+            }
+            Event::Mouse {
+                event: MouseEvent::Press(_),
+                position,
+                offset,
+            } => {
+                // eprintln!("Position: {:?} / {:?}", position, offset);
+                if let Some(position) = position.checked_sub(offset) {
+                    // Now `position` is relative to the top-left of the content.
+                    let focus = position.y;
+                    if !self.menu.children[focus].is_delimiter() {
+                        self.focus = focus;
+                    }
+                }
+            }
+            Event::Mouse {
+                event: MouseEvent::Release(MouseButton::Left),
+                position,
+                offset,
+            } if !self.menu.children[self.focus].is_delimiter()
+                && position
+                    .checked_sub(offset)
+                    .map(|position| position.y == self.focus)
+                    .unwrap_or(false) =>
+            {
+                return self.submit();
+            }
+            Event::Key(Key::Esc) => {
+                return self.dismiss();
+            }
+
+            _ => return EventResult::Ignored,
+        }
+
+        EventResult::Consumed(None)
+    }
+
+    /// Compute the required size for the content.
+    fn inner_required_size(&mut self, _req: Vec2) -> Vec2 {
+        let w = 2 + self
+            .menu
+            .children
+            .iter()
+            .map(Self::item_width)
+            .max()
+            .unwrap_or(1);
+
+        let h = self.menu.children.len();
+
+        Vec2::new(w, h)
+    }
+
+    fn inner_important_area(&self, size: Vec2) -> Rect {
+        if self.menu.is_empty() {
+            return Rect::from((0, 0));
+        }
+
+        Rect::from_size((0, self.focus), (size.x, 1))
+    }
 }
 
 impl View for MenuPopup {
@@ -121,14 +324,19 @@ impl View for MenuPopup {
         let printer = &printer.offset((0, offset));
 
         // Start with a box
-        printer.print_box(Vec2::new(0, 0), printer.size, false);
+        scroll::draw_box_frame(
+            self,
+            &printer,
+            |s, y| s.menu.children[y].is_delimiter(),
+            |_s, _x| false,
+        );
 
         // We're giving it a reduced size because of borders.
         let printer = printer.shrinked_centered((2, 2));
 
-        self.scrollbase.draw(&printer, |printer, i| {
+        scroll::draw_lines(self, &printer, |s, printer, i| {
-            printer.with_selection(i == self.focus, |printer| {
+            printer.with_selection(i == s.focus, |printer| {
-                let item = &self.menu.children[i];
+                let item = &s.menu.children[i];
                 match *item {
                     MenuItem::Delimiter => {
                         // printer.print_hdelim((0, 0), printer.size.x)
@@ -159,43 +367,38 @@ impl View for MenuPopup {
         // We can't really shrink our items here, so it's not flexible.
 
         // 2 is the padding
-        let w = 2 + self
-            .menu
-            .children
-            .iter()
-            .map(Self::item_width)
-            .max()
-            .unwrap_or(1);
 
-        let h = self.menu.children.len();
+        scroll::required_size(
-
+            self,
-        let res = self
+            req.saturating_sub((2, 2)),
-            .scrollbase
+            true,
-            .required_size(req.saturating_sub((2, 2)), |_| Vec2::new(w, h))
+            Self::inner_required_size,
-            + (2, 2);
+        ) + (2, 2)
-
-        res
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {
-        match self.scrollbase.on_event(
+        match scroll::on_event(
+            self,
             event.relativized((1, 1)),
-            OnEvent {
+            Self::inner_on_event,
-                focus: &mut self.focus,
+            Self::inner_important_area,
-                menu: &self.menu,
-                on_dismiss: &self.on_dismiss,
-                on_action: &self.on_action,
-                last_size: &self.last_size,
-            },
         ) {
             EventResult::Ignored => {
+                // Check back the non-relativized event now
                 if let Event::Mouse {
                     event: MouseEvent::Press(_),
                     position,
                     offset,
                 } = event
                 {
-                    if !position.fits_in_rect(offset, self.last_size) {
+                    // Mouse press will be ignored if they are outside of the content.
+                    // They can be on the border, or entirely outside of the popup.
+
+                    // Mouse clicks outside of the popup should dismiss it.
+                    if !position.fits_in_rect(
+                        offset,
+                        self.scroll_core.last_size() + (2, 2),
+                    ) {
                         let dismiss_cb = self.on_dismiss.clone();
                         return EventResult::with_cb(move |s| {
                             if let Some(ref cb) = dismiss_cb {
@@ -213,210 +416,21 @@ impl View for MenuPopup {
     }
 
     fn layout(&mut self, size: Vec2) {
-        self.last_size = size;
+        scroll::layout(
-
+            self,
-        let children = &self.menu.children;
+            size.saturating_sub((2, 2)),
-
+            true,
-        self.scrollbase.layout(size.saturating_sub((2, 2)), |size| {
+            |_s, _size| (),
-            Vec2::new(size.x, children.len())
+            Self::inner_required_size,
-        });
+        );
     }
 
     fn important_area(&self, size: Vec2) -> Rect {
-        if self.menu.is_empty() {
+        scroll::important_area(
-            return Rect::from((0, 0));
+            self,
-        }
+            size.saturating_sub((2, 2)),
-
+            Self::inner_important_area,
-        Rect::from_size((0, self.focus), (size.x, 1))
+        )
-    }
+        .with(|area| area.offset((1, 1)))
-}
-
-struct OnEvent<'a> {
-    focus: &'a mut usize,
-    menu: &'a Rc<MenuTree>,
-    on_dismiss: &'a Option<Callback>,
-    on_action: &'a Option<Callback>,
-    last_size: &'a Vec2,
-}
-
-impl<'a> OnEvent<'a> {
-    fn scroll_up(&mut self, mut n: usize, cycle: bool) {
-        while n > 0 {
-            if *self.focus > 0 {
-                *self.focus -= 1;
-            } else if cycle {
-                *self.focus = self.menu.children.len() - 1;
-            } else {
-                break;
-            }
-
-            if !self.menu.children[*self.focus].is_delimiter() {
-                n -= 1;
-            }
-        }
-    }
-
-    fn scroll_down(&mut self, mut n: usize, cycle: bool) {
-        while n > 0 {
-            if *self.focus + 1 < self.menu.children.len() {
-                *self.focus += 1;
-            } else if cycle {
-                *self.focus = 0;
-            } else {
-                break;
-            }
-            if !self.menu.children[*self.focus].is_delimiter() {
-                n -= 1;
-            }
-        }
-    }
-    fn submit(&mut self) -> EventResult {
-        match self.menu.children[*self.focus] {
-            MenuItem::Leaf(_, ref cb) => {
-                let cb = cb.clone();
-                let action_cb = self.on_action.clone();
-                EventResult::with_cb(move |s| {
-                    // Remove ourselves from the face of the earth
-                    s.pop_layer();
-                    // If we had prior orders, do it now.
-                    if let Some(ref action_cb) = action_cb {
-                        action_cb.clone()(s);
-                    }
-                    // And transmit his last words.
-                    cb.clone()(s);
-                })
-            }
-            MenuItem::Subtree(_, ref tree) => self.make_subtree_cb(tree),
-            _ => panic!("No delimiter here"),
-        }
-    }
-
-    fn dismiss(&mut self) -> EventResult {
-        let dismiss_cb = self.on_dismiss.clone();
-        EventResult::with_cb(move |s| {
-            if let Some(ref cb) = dismiss_cb {
-                cb.clone()(s);
-            }
-            s.pop_layer();
-        })
-    }
-
-    fn make_subtree_cb(&self, tree: &Rc<MenuTree>) -> EventResult {
-        let tree = Rc::clone(tree);
-        let max_width = 4 + self
-            .menu
-            .children
-            .iter()
-            .map(MenuPopup::item_width)
-            .max()
-            .unwrap_or(1);
-        let offset = Vec2::new(max_width, *self.focus);
-        let action_cb = self.on_action.clone();
-
-        EventResult::with_cb(move |s| {
-            let action_cb = action_cb.clone();
-            s.screen_mut().add_layer_at(
-                Position::parent(offset),
-                OnEventView::new(MenuPopup::new(Rc::clone(&tree)).on_action(
-                    move |s| {
-                        // This will happen when the subtree popup
-                        // activates something;
-                        // First, remove ourselve.
-                        s.pop_layer();
-                        if let Some(ref action_cb) = action_cb {
-                            action_cb.clone()(s);
-                        }
-                    },
-                ))
-                .on_event(Key::Left, |s| {
-                    s.pop_layer();
-                }),
-            );
-        })
-    }
-}
-
-impl<'a> InnerOnEvent for OnEvent<'a> {
-    fn on_event(&mut self, event: Event) -> EventResult {
-        match event {
-            Event::Key(Key::Up) => self.scroll_up(1, true),
-            Event::Key(Key::PageUp) => self.scroll_up(5, false),
-            Event::Key(Key::Down) => self.scroll_down(1, true),
-            Event::Key(Key::PageDown) => self.scroll_down(5, false),
-
-            Event::Key(Key::Home) => *self.focus = 0,
-            Event::Key(Key::End) => {
-                *self.focus = self.menu.children.len().saturating_sub(1)
-            }
-
-            Event::Key(Key::Right)
-                if self.menu.children[*self.focus].is_subtree() =>
-            {
-                return match self.menu.children[*self.focus] {
-                    MenuItem::Subtree(_, ref tree) => {
-                        self.make_subtree_cb(tree)
-                    }
-                    _ => panic!("Not a subtree???"),
-                };
-            }
-            Event::Key(Key::Enter)
-                if !self.menu.children[*self.focus].is_delimiter() =>
-            {
-                return self.submit();
-            }
-            Event::Mouse {
-                event: MouseEvent::Press(_),
-                position,
-                offset,
-            } if position.fits_in_rect(
-                offset,
-                self.last_size.saturating_sub((2, 2)),
-            ) =>
-            {
-                // eprintln!("Position: {:?} / {:?}", position, offset);
-                // eprintln!("Last size: {:?}", self.last_size);
-                let inner_size = self.last_size.saturating_sub((2, 2));
-                if let Some(position) = position.checked_sub(offset) {
-                    // `position` is not relative to the content
-                    // (It's inside the border)
-                    if position < inner_size {
-                        let focus = position.y;
-                        if !self.menu.children[focus].is_delimiter() {
-                            *self.focus = focus;
-                        }
-                    }
-                }
-            }
-            Event::Mouse {
-                event: MouseEvent::Release(MouseButton::Left),
-                position,
-                offset,
-            } if !self.menu.children[*self.focus].is_delimiter()
-                && position
-                    .checked_sub(offset)
-                    .map(|position| {
-                        position < self.last_size.saturating_sub((2, 2))
-                            && (position.y == *self.focus)
-                    })
-                    .unwrap_or(false) =>
-            {
-                return self.submit();
-            }
-            Event::Key(Key::Esc)
-            | Event::Mouse {
-                event: MouseEvent::Press(_),
-                ..
-            } => {
-                return self.dismiss();
-            }
-
-            _ => return EventResult::Ignored,
-        }
-
-        EventResult::Consumed(None)
-    }
-
-    fn important_area(&self, size: Vec2) -> Rect {
-        Rect::from_size((0, *self.focus), (size.x, 1))
     }
 }

src/views/scroll_view.rs

@@ -1,15 +1,26 @@
 use crate::direction::Direction;
 use crate::event::{AnyCb, Event, EventResult};
-use crate::rect::Rect;
 use crate::view::{scroll, ScrollStrategy, Selector, View};
-use crate::{Printer, Vec2, With};
+use crate::{Printer, Rect, Vec2, With};
 
 /// Wraps a view in a scrollable area.
 pub struct ScrollView<V> {
     /// The wrapped view.
     inner: V,
 
-    core: scroll::ScrollCore,
+    core: scroll::Core,
+}
+
+impl<V> scroll::Scroller for ScrollView<V>
+where
+    V: View,
+{
+    fn get_scroller(&self) -> &scroll::Core {
+        &self.core
+    }
+    fn get_scroller_mut(&mut self) -> &mut scroll::Core {
+        &mut self.core
+    }
 }
 
 impl<V> ScrollView<V>
@@ -20,7 +31,7 @@ where
     pub fn new(inner: V) -> Self {
         ScrollView {
             inner,
-            core: scroll::ScrollCore::new(),
+            core: scroll::Core::new(),
         }
     }
 
@@ -134,23 +145,39 @@ where
     V: View,
 {
     fn draw(&self, printer: &Printer<'_, '_>) {
-        self.core.draw(printer, |printer| self.inner.draw(printer));
+        scroll::draw(self, printer, |s, p| s.inner.draw(p));
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {
-        self.core.on_event(event, &mut self.inner)
+        scroll::on_event(
+            self,
+            event,
+            |s, e| s.inner.on_event(e),
+            |s, si| s.inner.important_area(si),
+        )
     }
 
     fn layout(&mut self, size: Vec2) {
-        self.core.layout(size, &mut self.inner);
+        scroll::layout(
+            self,
+            size,
+            self.inner.needs_relayout(),
+            |s, si| s.inner.layout(si),
+            |s, c| s.inner.required_size(c),
+        );
     }
 
     fn needs_relayout(&self) -> bool {
-        self.core.needs_relayout(|| self.inner.needs_relayout())
+        self.core.needs_relayout() || self.inner.needs_relayout()
     }
 
     fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        self.core.required_size(constraint, &mut self.inner)
+        scroll::required_size(
+            self,
+            constraint,
+            self.inner.needs_relayout(),
+            |s, c| s.inner.required_size(c),
+        )
     }
 
     fn call_on_any<'a>(&mut self, selector: &Selector<'_>, cb: AnyCb<'a>) {
@@ -162,8 +189,10 @@ where
     }
 
     fn take_focus(&mut self, source: Direction) -> bool {
-        let inner = &mut self.inner;
+        self.inner.take_focus(source) || self.core.is_scrolling().any()
-        self.core
+    }
-            .take_focus(source, |source| inner.take_focus(source))
+
+    fn important_area(&self, size: Vec2) -> Rect {
+        scroll::important_area(self, size, |s, si| s.inner.important_area(si))
     }
 }