Fix linear layout in constrained space

examples/linear.rs

@@ -1,19 +1,19 @@
 extern crate cursive;
 
 use cursive::Cursive;
-use cursive::view::{Dialog,TextView,LinearLayout,BoxView};
+use cursive::view::{BoxView, Dialog, LinearLayout, TextView};
 use cursive::align::HAlign;
 
 fn main() {
     let mut siv = Cursive::new();
 
     // Some description text
-    let text = "This is a very simple example of linear layout. Two views are present, a short title above, and this text. The text has a fixed width, and the title is centered horizontally.";
+    let text = "This is a very simple example of linear layout. Two views \
+                are present, a short title above, and this text. The text \
+                has a fixed width, and the title is centered horizontally.";
 
     // We'll create a dialog with a TextView serving as a title
-    siv.add_layer(
+    siv.add_layer(Dialog::new(LinearLayout::vertical()
-        Dialog::new(
-            LinearLayout::vertical()
             .child(TextView::new("Title").h_align(HAlign::Center))
             // Box the textview, so it doesn't get too wide.
             // A 0 height value means it will be unconstrained.

src/orientation.rs

@@ -54,4 +54,11 @@ impl Orientation {
             }
         }
     }
+
+    /// Creates a new `Vec2` with `value` in `self`'s axis.
+    pub fn make_vec(&self, value: usize) -> Vec2 {
+        let mut result = Vec2::zero();
+        *self.get_ref(&mut result) = value;
+        result
+    }
 }

src/printer.rs

@@ -175,11 +175,11 @@ impl Printer {
     /// Returns a printer on a subset of this one's area.
     pub fn sub_printer<S: Into<Vec2>>(&self, offset: S, size: S, focused: bool)
                                       -> Printer {
-        let offset_v = offset.into();
+        let offset = offset.into().or_min(self.size);
         Printer {
-            offset: self.offset + offset_v,
+            offset: self.offset + offset,
             // We can't be larger than what remains
-            size: Vec2::min(self.size - offset_v, size.into()),
+            size: Vec2::min(self.size - offset, size.into()),
             focused: self.focused && focused,
             theme: self.theme.clone(),
         }

src/vec.rs

@@ -1,5 +1,6 @@
 //! Points on the 2D character grid.
 use XY;
+use orientation::Orientation;
 
 use std::ops::{Add, Div, Mul, Sub};
 use std::cmp::{Ordering, max, min};
@@ -70,6 +71,21 @@ impl Vec2 {
     pub fn stack_horizontal(&self, other: &Vec2) -> Vec2 {
         Vec2::new(self.x + other.x, max(self.y, other.y))
     }
+
+    /// Returns `true` if `self` could fit inside `other`.
+    ///
+    /// Shortcut for `self.x <= other.x && self.y <= other.y`.
+    pub fn fits_in<T: Into<Vec2>>(&self, other: T) -> bool {
+        let other = other.into();
+        self.x <= other.x && self.y <= other.y
+    }
+
+    /// Returns a new `Vec2` with the axis `o` set to `value`.
+    pub fn with(&self, o: Orientation, value: usize) -> Self {
+        let mut other = self.clone();
+        *o.get_ref(&mut other) = value;
+        other
+    }
 }
 
 impl From<(i32, i32)> for Vec2 {

src/view/box_view.rs

@@ -68,6 +68,6 @@ impl<T: View> ViewWrapper for BoxView<T> {
 
             Vec2::new(self.size.x.unwrap_or(child_size.x),
                       self.size.y.unwrap_or(child_size.y))
-        }
+        }.or_min(req)
     }
 }

src/view/linear_layout.rs

@@ -1,16 +1,20 @@
+use XY;
 use view::View;
+use view::SizeCache;
 use vec::Vec2;
 use printer::Printer;
 use orientation::Orientation;
 use event::{Event, EventResult, Key};
 
+use std::cmp::min;
+
 /// Arranges its children linearly according to its orientation.
 pub struct LinearLayout {
     children: Vec<Child>,
     orientation: Orientation,
     focus: usize,
 
-    last_size: Option<Vec2>,
+    cache: Option<XY<SizeCache>>,
 }
 
 struct Child {
@@ -19,6 +23,13 @@ struct Child {
     weight: usize,
 }
 
+impl Child {
+    fn get_min_size(&mut self, req: Vec2) -> Vec2 {
+        self.size = self.view.get_min_size(req);
+        self.size
+    }
+}
+
 impl LinearLayout {
     /// Creates a new layout with the given orientation.
     pub fn new(orientation: Orientation) -> Self {
@@ -26,7 +37,7 @@ impl LinearLayout {
             children: Vec::new(),
             orientation: orientation,
             focus: 0,
-            last_size: None,
+            cache: None,
         }
     }
 
@@ -46,11 +57,16 @@ impl LinearLayout {
             size: Vec2::zero(),
             weight: 0,
         });
-        self.last_size = None;
+        self.invalidate();
 
         self
     }
 
+    // Invalidate the view, to request a layout next time
+    fn invalidate(&mut self) {
+        self.cache = None;
+    }
+
     /// Creates a new vertical layout.
     pub fn vertical() -> Self {
         LinearLayout::new(Orientation::Vertical)
@@ -60,6 +76,31 @@ impl LinearLayout {
     pub fn horizontal() -> Self {
         LinearLayout::new(Orientation::Horizontal)
     }
+
+    // If the cache can be used, return the cached size.
+    // Otherwise, return None.
+    fn get_cache(&self, req: Vec2) -> Option<Vec2> {
+        match self.cache {
+            None => None,
+            Some(ref cache) => {
+                // Is our cache even valid?
+                // Also, is any child invalidating the layout?
+                if cache.x.accept(req.x) && cache.y.accept(req.y) &&
+                   self.children_are_sleeping() {
+                    Some(cache.map(|s| s.value))
+                } else {
+                    None
+                }
+            }
+        }
+    }
+
+    fn children_are_sleeping(&self) -> bool {
+        !self.children
+            .iter()
+            .map(|c| &*c.view)
+            .any(View::needs_relayout)
+    }
 }
 
 /// Returns the index of the maximum element.
@@ -129,23 +170,29 @@ impl View for LinearLayout {
     }
 
     fn needs_relayout(&self) -> bool {
-        if self.last_size == None {
+        if self.cache.is_none() {
             return true;
         }
 
-        for child in &self.children {
+        !self.children_are_sleeping()
-            if child.view.needs_relayout() {
-                return true;
-            }
-        }
-
-        false
     }
 
     fn layout(&mut self, size: Vec2) {
-        // Compute the very minimal required size
+        // If we can get away without breaking a sweat, you can bet we will.
-        // Look how mean we are: we offer the whole size to every child.
+        if self.get_cache(size).is_none() {
-        // As if they could get it all.
+            self.get_min_size(size);
+        }
+
+        for child in &mut self.children {
+            // println_stderr!("Child size: {:?}", child.size);
+            child.view.layout(child.size);
+        }
+
+        /*
+
+        // Need to compute things again...
+        self.get_min_size(size);
+
         let min_sizes: Vec<Vec2> = self.children
             .iter_mut()
             .map(|child| Vec2::min(size, child.view.get_min_size(size)))
@@ -180,26 +227,104 @@ impl View for LinearLayout {
             child.size = child_size;
             child.view.layout(child_size);
         }
+        */
     }
 
     fn get_min_size(&mut self, req: Vec2) -> Vec2 {
+        // Did anything change since last time?
+        if let Some(size) = self.get_cache(req) {
+            return size;
+        }
+
         // First, make a naive scenario: everything will work fine.
         let sizes: Vec<Vec2> = self.children
             .iter_mut()
-            .map(|view| view.view.get_min_size(req))
+            .map(|c| c.get_min_size(req))
             .collect();
-        self.orientation.stack(sizes.iter())
+        // println_stderr!("Ideal sizes: {:?}", sizes);
+        let ideal = self.orientation.stack(sizes.iter());
+        // println_stderr!("Ideal result: {:?}", ideal);
 
 
-        // Did it work? Champagne!
+        // Does it fit?
+        if ideal.fits_in(req) {
+            // Champagne!
+            self.cache = Some(SizeCache::build(ideal, req));
+            return ideal;
+        }
+
+        // Ok, so maybe it didn't.
+        // Budget cuts, everyone.
+        let budget_req = req.with(self.orientation, 1);
+        // println_stderr!("Budget req: {:?}", budget_req);
+
+        let min_sizes: Vec<Vec2> = self.children
+            .iter_mut()
+            .map(|c| c.get_min_size(budget_req))
+            .collect();
+        let desperate = self.orientation.stack(min_sizes.iter());
+        // println_stderr!("Min sizes: {:?}", min_sizes);
+        // println_stderr!("Desperate: {:?}", desperate);
+
+        // I really hope it fits this time...
+        if !desperate.fits_in(req) {
+            // Just give up...
+            // println_stderr!("Seriously? {:?} > {:?}???", desperate, req);
+            self.cache = Some(SizeCache::build(desperate, req));
+            return desperate;
+        }
+
+        // This here is how much we're generously offered
+        let mut available = self.orientation.get(&(req - desperate));
+        // println_stderr!("Available: {:?}", available);
+
+        // Here, we have to make a compromise between the ideal
+        // and the desperate solutions.
+        let mut overweight: Vec<(usize, usize)> = sizes.iter()
+            .map(|v| self.orientation.get(v))
+            .zip(min_sizes.iter().map(|v| self.orientation.get(v)))
+            .map(|(a, b)| a - b)
+            .enumerate()
+            .collect();
+        // println_stderr!("Overweight: {:?}", overweight);
+
+        // So... distribute `available` to reduce the overweight...
+        // TODO: use child weight in the distribution...
+        overweight.sort_by_key(|&(_, weight)| weight);
+        let mut allocations = vec![0; overweight.len()];
+
+        for (i, &(j, weight)) in overweight.iter().enumerate() {
+            let remaining = overweight.len() - i;
+            let budget = available / remaining;
+            let spent = min(budget, weight);
+            allocations[j] = spent;
+            available -= spent;
+        }
+        // println_stderr!("Allocations: {:?}", allocations);
+
+        // Final lengths are the minimum ones + allocations
+        let final_lengths: Vec<Vec2> = min_sizes.iter()
+            .map(|v| self.orientation.get(v))
+            .zip(allocations.iter())
+            .map(|(a, b)| a + b)
+            .map(|l| req.with(self.orientation, l))
+            .collect();
+        // println_stderr!("Final sizes: {:?}", final_lengths);
+
+        let final_sizes: Vec<Vec2> = self.children
+            .iter_mut()
+            .enumerate()
+            .map(|(i, c)| {
+                c.get_min_size(final_lengths[i])
+            })
+            .collect();
+        // println_stderr!("Final sizes2: {:?}", final_sizes);
 
 
-        // TODO: Ok, so maybe it didn't.
+        let compromise = self.orientation.stack(final_sizes.iter());
-        // Last chance: did someone lie about his needs?
+        self.cache = Some(SizeCache::build(compromise, req));
-        // Could we squash him a little?
-        // (Maybe he'll just scroll and it'll be fine?)
 
-        // Find out who's fluid, if any.
+        compromise
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {

src/view/mod.rs

@@ -30,6 +30,7 @@ mod tracked_view;
 
 use std::any::Any;
 
+use XY;
 use event::{Event, EventResult};
 use vec::Vec2;
 use printer::Printer;
@@ -105,6 +106,49 @@ pub trait View {
     }
 }
 
+/// Cache around a one-dimensional layout result
+#[derive(PartialEq, Debug, Clone, Copy)]
+pub struct SizeCache {
+    /// Cached value
+    pub value: usize,
+    /// `true` if the last size was constrained.
+    ///
+    /// If unconstrained, any request larger than this value
+    /// would return the same size.
+    pub constrained: bool,
+}
+
+impl SizeCache {
+    /// Creates a new sized cache
+    pub fn new(value: usize, constrained: bool) -> Self {
+        SizeCache {
+            value: value,
+            constrained: constrained,
+        }
+    }
+
+    /// Returns `true` if `self` is still valid for the given `request`.
+    pub fn accept(&self, request: usize) -> bool {
+        if request < self.value {
+            false
+        } else if request == self.value {
+            true
+        } else {
+            !self.constrained
+        }
+    }
+
+    /// Creates a new bi-dimensional cache.
+    ///
+    /// * `size` must fit inside `req`.
+    /// * for each dimension, `constrained = (size == req)`
+    fn build(size: Vec2, req: Vec2) -> XY<Self> {
+        XY::new(SizeCache::new(size.x, size.x == req.x),
+        SizeCache::new(size.y, size.y == req.y))
+    }
+}
+
+
 /// Selects a single view (if any) in the tree.
 pub enum Selector<'a> {
     /// Selects a view from its ID

src/view/text_view.rs

@@ -1,6 +1,7 @@
 use XY;
 use vec::Vec2;
 use view::View;
+use view::SizeCache;
 use printer::Printer;
 use align::*;
 use event::*;
@@ -9,38 +10,6 @@ use super::scroll::ScrollBase;
 use unicode_width::UnicodeWidthStr;
 use unicode_segmentation::UnicodeSegmentation;
 
-#[derive(PartialEq, Debug, Clone)]
-struct SizeCache {
-    value: usize,
-    // If unconstrained, any request larger than this value
-    // would return the same size.
-    constrained: bool,
-}
-
-impl SizeCache {
-    fn new(value: usize, constrained: bool) -> Self {
-        SizeCache {
-            value: value,
-            constrained: constrained,
-        }
-    }
-
-    fn accept(&self, size: usize) -> bool {
-        if size < self.value {
-            false
-        } else if size == self.value {
-            true
-        } else {
-            !self.constrained
-        }
-    }
-}
-
-fn cache_size(size: Vec2, req: Vec2) -> XY<SizeCache> {
-    XY::new(SizeCache::new(size.x, size.x == req.x),
-            SizeCache::new(size.y, size.y == req.y))
-
-}
 
 /// A simple view showing a fixed text
 pub struct TextView {
@@ -147,7 +116,7 @@ impl TextView {
             // Our resulting size.
             let my_size =
                 size.or_min((self.width.unwrap_or(0), self.rows.len()));
-            self.last_size = Some(cache_size(my_size, size));
+            self.last_size = Some(SizeCache::build(my_size, size));
         }
     }
 
@@ -267,7 +236,7 @@ impl View for TextView {
 
     fn get_min_size(&mut self, size: Vec2) -> Vec2 {
         self.compute_rows(size);
-        Vec2::new(self.width.unwrap_or(0), self.rows.len())
+        size.or_min((self.width.unwrap_or(0), self.rows.len()))
     }
 
     fn take_focus(&mut self) -> bool {

src/xy.rs

@@ -15,6 +15,11 @@ impl<T> XY<T> {
         XY { x: x, y: y }
     }
 
+    /// Creates a new `XY` by applying `f` to `x` and `y`.
+    pub fn map<U, F: Fn(T) -> U>(self, f: F) -> XY<U> {
+        XY::new(f(self.x), f(self.y))
+    }
+
     /// Destructure self into a pair.
     pub fn pair(self) -> (T, T) {
         (self.x, self.y)