Getting back to where we started... (Buggy Resizing)

Cargo.lock

@@ -271,6 +271,12 @@ version = "1.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "631ae5198c9be5e753e5cc215e1bd73c2b466a3565173db433f52bb9d3e66dba"
 
+[[package]]
+name = "cassowary"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df8670b8c7b9dae1793364eafadf7239c40d669904660c5960d74cfd80b46a53"
+
 [[package]]
 name = "cc"
 version = "1.0.67"
@@ -2345,6 +2351,7 @@ version = "0.13.0"
 dependencies = [
  "ansi_term 0.12.1",
  "async-trait",
+ "cassowary",
  "daemonize",
  "insta",
  "serde_json",

default-plugins/status-bar/src/main.rs

@@ -135,7 +135,7 @@ impl ZellijPlugin for State {
     fn load(&mut self) {
         set_selectable(false);
         set_invisible_borders(true);
-        set_max_height(2);
+        set_fixed_height(2);
         subscribe(&[EventType::ModeUpdate]);
     }
 

default-plugins/tab-bar/src/main.rs

@@ -26,7 +26,7 @@ impl ZellijPlugin for State {
     fn load(&mut self) {
         set_selectable(false);
         set_invisible_borders(true);
-        set_max_height(1);
+        set_fixed_height(1);
         subscribe(&[EventType::TabUpdate, EventType::ModeUpdate]);
     }
 

zellij-server/Cargo.toml

@@ -16,6 +16,7 @@ serde_json = "1.0"
 unicode-width = "0.1.8"
 wasmer = "1.0.0"
 wasmer-wasi = "1.0.0"
+cassowary = "0.3.0"
 zellij-utils = { path = "../zellij-utils/", version = "0.13.0" }
 
 [dev-dependencies]

zellij-server/src/lib.rs

@@ -112,6 +112,8 @@ pub fn start_server(os_input: Box<dyn ServerOsApi>, socket_path: PathBuf) {
     daemonize::Daemonize::new()
         .working_directory(std::env::current_dir().unwrap())
         .umask(0o077)
+        // FIXME: My cherished `dbg!` was broken, so this is a hack to bring it back
+        .stderr(std::fs::File::create("dbg.log").unwrap())
         .start()
         .expect("could not daemonize the server process");
 

zellij-server/src/panes/plugin_pane.rs

@@ -16,8 +16,6 @@ pub(crate) struct PluginPane {
     pub position_and_size: PositionAndSize,
     pub position_and_size_override: Option<PositionAndSize>,
     pub send_plugin_instructions: SenderWithContext<PluginInstruction>,
-    pub max_height: Option<usize>,
-    pub max_width: Option<usize>,
     pub active_at: Instant,
 }
 
@@ -35,8 +33,6 @@ impl PluginPane {
             position_and_size,
             position_and_size_override: None,
             send_plugin_instructions,
-            max_height: None,
-            max_width: None,
             active_at: Instant::now(),
         }
     }
@@ -95,7 +91,9 @@ impl Pane for PluginPane {
     fn adjust_input_to_terminal(&self, _input_bytes: Vec<u8>) -> Vec<u8> {
         unimplemented!() // FIXME: Shouldn't need this implmented?
     }
-
+    fn position_and_size(&self) -> PositionAndSize {
+        self.position_and_size
+    }
     fn position_and_size_override(&self) -> Option<PositionAndSize> {
         self.position_and_size_override
     }
@@ -114,11 +112,13 @@ impl Pane for PluginPane {
     fn set_invisible_borders(&mut self, invisible_borders: bool) {
         self.invisible_borders = invisible_borders;
     }
-    fn set_max_height(&mut self, max_height: usize) {
+    fn set_fixed_height(&mut self, fixed_height: usize) {
-        self.max_height = Some(max_height);
+        self.position_and_size.rows = fixed_height;
+        self.position_and_size.rows_fixed = true;
     }
-    fn set_max_width(&mut self, max_width: usize) {
+    fn set_fixed_width(&mut self, fixed_width: usize) {
-        self.max_width = Some(max_width);
+        self.position_and_size.columns = fixed_width;
+        self.position_and_size.cols_fixed = true;
     }
     fn render(&mut self) -> Option<String> {
         // if self.should_render {
@@ -204,11 +204,21 @@ impl Pane for PluginPane {
     fn clear_scroll(&mut self) {
         unimplemented!()
     }
+    // FIXME: This need to be reevaluated and deleted if possible.
+    // `max` doesn't make sense when things are fixed...
     fn max_height(&self) -> Option<usize> {
-        self.max_height
+        if self.position_and_size.rows_fixed {
+            Some(self.position_and_size.rows)
+        } else {
+            None
+        }
     }
     fn max_width(&self) -> Option<usize> {
-        self.max_width
+        if self.position_and_size.cols_fixed {
+            Some(self.position_and_size.columns)
+        } else {
+            None
+        }
     }
     fn invisible_borders(&self) -> bool {
         self.invisible_borders

zellij-server/src/panes/terminal_pane.rs

@@ -27,8 +27,6 @@ pub struct TerminalPane {
     pub selectable: bool,
     pub position_and_size: PositionAndSize,
     pub position_and_size_override: Option<PositionAndSize>,
-    pub max_height: Option<usize>,
-    pub max_width: Option<usize>,
     pub active_at: Instant,
     pub colors: Palette,
     vte_parser: vte::Parser,
@@ -52,8 +50,7 @@ impl Pane for TerminalPane {
         self.reflow_lines();
     }
     fn change_pos_and_size(&mut self, position_and_size: &PositionAndSize) {
-        self.position_and_size.columns = position_and_size.columns;
+        self.position_and_size = *position_and_size;
-        self.position_and_size.rows = position_and_size.rows;
         self.reflow_lines();
     }
     fn override_size_and_position(&mut self, x: usize, y: usize, size: &PositionAndSize) {
@@ -119,7 +116,9 @@ impl Pane for TerminalPane {
         };
         input_bytes
     }
-
+    fn position_and_size(&self) -> PositionAndSize {
+        self.position_and_size
+    }
     fn position_and_size_override(&self) -> Option<PositionAndSize> {
         self.position_and_size_override
     }
@@ -135,21 +134,17 @@ impl Pane for TerminalPane {
     fn set_selectable(&mut self, selectable: bool) {
         self.selectable = selectable;
     }
-    fn set_max_height(&mut self, max_height: usize) {
+    fn set_fixed_height(&mut self, fixed_height: usize) {
-        self.max_height = Some(max_height);
+        self.position_and_size.rows = fixed_height;
+        self.position_and_size.rows_fixed = true;
     }
-    fn set_max_width(&mut self, max_width: usize) {
+    fn set_fixed_width(&mut self, fixed_width: usize) {
-        self.max_width = Some(max_width);
+        self.position_and_size.columns = fixed_width;
+        self.position_and_size.cols_fixed = true;
     }
     fn set_invisible_borders(&mut self, _invisible_borders: bool) {
         unimplemented!();
     }
-    fn max_height(&self) -> Option<usize> {
-        self.max_height
-    }
-    fn max_width(&self) -> Option<usize> {
-        self.max_width
-    }
     fn render(&mut self) -> Option<String> {
         if self.should_render() {
             let mut vte_output = String::new();
@@ -294,8 +289,6 @@ impl TerminalPane {
             selectable: true,
             position_and_size,
             position_and_size_override: None,
-            max_height: None,
-            max_width: None,
             vte_parser: vte::Parser::new(),
             active_at: Instant::now(),
             colors: palette,

zellij-server/src/screen.rs

@@ -55,7 +55,8 @@ pub(crate) enum ScreenInstruction {
     CloseFocusedPane,
     ToggleActiveTerminalFullscreen,
     SetSelectable(PaneId, bool),
-    SetMaxHeight(PaneId, usize),
+    SetFixedHeight(PaneId, usize),
+    SetFixedWidth(PaneId, usize),
     SetInvisibleBorders(PaneId, bool),
     ClosePane(PaneId),
     ApplyLayout(Layout, Vec<RawFd>),
@@ -106,7 +107,8 @@ impl From<&ScreenInstruction> for ScreenContext {
             }
             ScreenInstruction::SetSelectable(..) => ScreenContext::SetSelectable,
             ScreenInstruction::SetInvisibleBorders(..) => ScreenContext::SetInvisibleBorders,
-            ScreenInstruction::SetMaxHeight(..) => ScreenContext::SetMaxHeight,
+            ScreenInstruction::SetFixedHeight(..) => ScreenContext::SetFixedHeight,
+            ScreenInstruction::SetFixedWidth(..) => ScreenContext::SetFixedWidth,
             ScreenInstruction::ClosePane(_) => ScreenContext::ClosePane,
             ScreenInstruction::ApplyLayout(..) => ScreenContext::ApplyLayout,
             ScreenInstruction::NewTab(_) => ScreenContext::NewTab,
@@ -574,11 +576,17 @@ pub(crate) fn screen_thread_main(
                     .unwrap()
                     .set_pane_selectable(id, selectable);
             }
-            ScreenInstruction::SetMaxHeight(id, max_height) => {
+            ScreenInstruction::SetFixedHeight(id, fixed_height) => {
                 screen
                     .get_active_tab_mut()
                     .unwrap()
-                    .set_pane_max_height(id, max_height);
+                    .set_pane_fixed_height(id, fixed_height);
+            }
+            ScreenInstruction::SetFixedWidth(id, fixed_width) => {
+                screen
+                    .get_active_tab_mut()
+                    .unwrap()
+                    .set_pane_fixed_width(id, fixed_width);
             }
             ScreenInstruction::SetInvisibleBorders(id, invisible_borders) => {
                 screen

zellij-server/src/tab.rs

@@ -104,15 +104,15 @@ pub trait Pane {
     fn handle_pty_bytes(&mut self, bytes: VteBytes);
     fn cursor_coordinates(&self) -> Option<(usize, usize)>;
     fn adjust_input_to_terminal(&self, input_bytes: Vec<u8>) -> Vec<u8>;
-
+    fn position_and_size(&self) -> PositionAndSize;
     fn position_and_size_override(&self) -> Option<PositionAndSize>;
     fn should_render(&self) -> bool;
     fn set_should_render(&mut self, should_render: bool);
     fn selectable(&self) -> bool;
     fn set_selectable(&mut self, selectable: bool);
     fn set_invisible_borders(&mut self, invisible_borders: bool);
-    fn set_max_height(&mut self, max_height: usize);
+    fn set_fixed_height(&mut self, fixed_height: usize);
-    fn set_max_width(&mut self, max_width: usize);
+    fn set_fixed_width(&mut self, fixed_width: usize);
     fn render(&mut self) -> Option<String>;
     fn pid(&self) -> PaneId;
     fn reduce_height_down(&mut self, count: usize);
@@ -178,15 +178,6 @@ pub trait Pane {
         std::cmp::min(self.x() + self.columns(), other.x() + other.columns())
             - std::cmp::max(self.x(), other.x())
     }
-    fn position_and_size(&self) -> PositionAndSize {
-        PositionAndSize {
-            x: self.x(),
-            y: self.y(),
-            columns: self.columns(),
-            rows: self.rows(),
-            ..Default::default()
-        }
-    }
     fn can_increase_height_by(&self, increase_by: usize) -> bool {
         self.max_height()
             .map(|max_height| self.rows() + increase_by <= max_height)
@@ -294,12 +285,6 @@ impl Tab {
                 match positions_and_size.next() {
                     Some((_, position_and_size)) => {
                         terminal_pane.reset_size_and_position_override();
-                        if let Some(max_rows) = position_and_size.max_rows {
-                            terminal_pane.set_max_height(max_rows);
-                        }
-                        if let Some(max_columns) = position_and_size.max_columns {
-                            terminal_pane.set_max_width(max_columns);
-                        }
                         terminal_pane.change_pos_and_size(&position_and_size);
                         self.os_api.set_terminal_size_using_fd(
                             *pid,
@@ -317,24 +302,18 @@ impl Tab {
         }
         let mut new_pids = new_pids.iter();
         for (layout, position_and_size) in positions_and_size {
-            // Just a regular terminal
+            // A plugin pane
             if let Some(plugin) = &layout.plugin {
                 let (pid_tx, pid_rx) = channel();
                 self.senders
                     .send_to_plugin(PluginInstruction::Load(pid_tx, plugin.clone()))
                     .unwrap();
                 let pid = pid_rx.recv().unwrap();
-                let mut new_plugin = PluginPane::new(
+                let new_plugin = PluginPane::new(
                     pid,
                     *position_and_size,
                     self.senders.to_plugin.as_ref().unwrap().clone(),
                 );
-                if let Some(max_rows) = position_and_size.max_rows {
-                    new_plugin.set_max_height(max_rows);
-                }
-                if let Some(max_columns) = position_and_size.max_columns {
-                    new_plugin.set_max_width(max_columns);
-                }
                 self.panes.insert(PaneId::Plugin(pid), Box::new(new_plugin));
                 // Send an initial mode update to the newly loaded plugin only!
                 self.senders
@@ -2121,9 +2100,14 @@ impl Tab {
             pane.set_invisible_borders(invisible_borders);
         }
     }
-    pub fn set_pane_max_height(&mut self, id: PaneId, max_height: usize) {
+    pub fn set_pane_fixed_height(&mut self, id: PaneId, fixed_height: usize) {
         if let Some(pane) = self.panes.get_mut(&id) {
-            pane.set_max_height(max_height);
+            pane.set_fixed_height(fixed_height);
+        }
+    }
+    pub fn set_pane_fixed_width(&mut self, id: PaneId, fixed_width: usize) {
+        if let Some(pane) = self.panes.get_mut(&id) {
+            pane.set_fixed_width(fixed_width);
         }
     }
     pub fn close_pane(&mut self, id: PaneId) {

zellij-server/src/ui/layout.rs

@@ -19,17 +19,14 @@ fn split_space_to_parts_vertically(
 
     // First fit in the parameterized sizes
     for size in sizes {
-        let (columns, max_columns) = match size {
+        let columns = match size {
             Some(SplitSize::Percent(percent)) => {
-                ((max_width as f32 * (percent as f32 / 100.0)) as usize, None)
+                (max_width as f32 * (percent as f32 / 100.0)) as usize
             } // TODO: round properly
-            Some(SplitSize::Fixed(size)) => (size as usize, Some(size as usize)),
+            Some(SplitSize::Fixed(size)) => size as usize,
             None => {
                 parts_to_grow.push(current_x_position);
-                (
+                1 // This is grown later on
-                    1, // This is grown later on
-                    None,
-                )
             }
         };
         split_parts.push(PositionAndSize {
@@ -37,7 +34,6 @@ fn split_space_to_parts_vertically(
             y: space_to_split.y,
             columns,
             rows: space_to_split.rows,
-            max_columns,
             ..Default::default()
         });
         current_width += columns;
@@ -87,18 +83,14 @@ fn split_space_to_parts_horizontally(
     let mut parts_to_grow = Vec::new();
 
     for size in sizes {
-        let (rows, max_rows) = match size {
+        let rows = match size {
-            Some(SplitSize::Percent(percent)) => (
+            Some(SplitSize::Percent(percent)) => {
-                (max_height as f32 * (percent as f32 / 100.0)) as usize,
+                (max_height as f32 * (percent as f32 / 100.0)) as usize
-                None,
+            } // TODO: round properly
-            ), // TODO: round properly
+            Some(SplitSize::Fixed(size)) => size as usize,
-            Some(SplitSize::Fixed(size)) => (size as usize, Some(size as usize)),
             None => {
                 parts_to_grow.push(current_y_position);
-                (
+                1 // This is grown later on
-                    1, // This is grown later on
-                    None,
-                )
             }
         };
         split_parts.push(PositionAndSize {
@@ -106,7 +98,6 @@ fn split_space_to_parts_horizontally(
             y: current_y_position,
             columns: space_to_split.columns,
             rows,
-            max_rows,
             ..Default::default()
         });
         current_height += rows;

zellij-server/src/ui/pane_resizer.rs

@@ -1,531 +1,247 @@
 use crate::{os_input_output::ServerOsApi, panes::PaneId, tab::Pane};
+use cassowary::{
+    strength::{REQUIRED, STRONG},
+    Constraint, Solver, Variable,
+    WeightedRelation::*,
+};
 use std::{
-    cmp::Ordering,
     collections::{BTreeMap, HashSet},
+    ops::Not,
 };
 use zellij_utils::pane_size::PositionAndSize;
 
-pub(crate) struct PaneResizer<'a> {
+const GAP_SIZE: usize = 1; // Panes are separated by this number of rows / columns
+
+pub struct PaneResizer<'a> {
     panes: &'a mut BTreeMap<PaneId, Box<dyn Pane>>,
+    vars: BTreeMap<PaneId, (Variable, Variable)>,
+    solver: Solver,
     os_api: &'a mut Box<dyn ServerOsApi>,
 }
 
+#[derive(Debug, Clone, Copy)]
+enum Direction {
+    Horizontal,
+    Vertical,
+}
+
+impl Not for Direction {
+    type Output = Self;
+
+    fn not(self) -> Self::Output {
+        match self {
+            Direction::Horizontal => Direction::Vertical,
+            Direction::Vertical => Direction::Horizontal,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Span {
+    pid: PaneId,
+    direction: Direction,
+    fixed: bool,
+    pos: usize,
+    size: usize,
+    pos_var: Variable,
+    size_var: Variable,
+}
+
 // TODO: currently there are some functions here duplicated with Tab
 // all resizing functions should move here
 
+// FIXME:
+// 1. Rounding causes a loss of ratios, I need to store an internal f64 for
+//    each pane as well as the displayed usize and add custom rounding logic.
+// 2. Vertical resizing doesn't seem to respect the space consumed by the tab
+//    and status bars?
+// 3. A 2x2 layout and simultaneous vertical + horizontal resizing sometimes
+//    leads to unsolvable constraints? Maybe related to 2 (and possibly 1).
+//    I should sanity-check the `spans_in_boundary()` here!
+
 impl<'a> PaneResizer<'a> {
     pub fn new(
         panes: &'a mut BTreeMap<PaneId, Box<dyn Pane>>,
         os_api: &'a mut Box<dyn ServerOsApi>,
     ) -> Self {
-        PaneResizer { panes, os_api }
+        let mut vars = BTreeMap::new();
+        for &k in panes.keys() {
+            vars.insert(k, (Variable::new(), Variable::new()));
+        }
+        PaneResizer {
+            panes,
+            vars,
+            solver: Solver::new(),
+            os_api,
+        }
     }
+
     pub fn resize(
         &mut self,
-        mut current_size: PositionAndSize,
+        current_size: PositionAndSize,
         new_size: PositionAndSize,
     ) -> Option<(isize, isize)> {
-        // (column_difference, row_difference)
+        let col_delta = new_size.columns as isize - current_size.columns as isize;
-        let mut successfully_resized = false;
+        let row_delta = new_size.rows as isize - current_size.rows as isize;
-        let mut column_difference: isize = 0;
+        if col_delta != 0 {
-        let mut row_difference: isize = 0;
+            let spans = self.solve_direction(Direction::Horizontal, new_size.columns)?;
-        match new_size.columns.cmp(&current_size.columns) {
+            self.collapse_spans(&spans);
-            Ordering::Greater => {
-                let increase_by = new_size.columns - current_size.columns;
-                if let Some(panes_to_resize) = find_increasable_vertical_chain(
-                    &self.panes,
-                    increase_by,
-                    current_size.columns,
-                    current_size.rows,
-                ) {
-                    self.increase_panes_right_and_push_adjacents_right(
-                        panes_to_resize,
-                        increase_by,
-                    );
-                    column_difference = new_size.columns as isize - current_size.columns as isize;
-                    current_size.columns =
-                        (current_size.columns as isize + column_difference) as usize;
-                    successfully_resized = true;
-                };
-            }
-            Ordering::Less => {
-                let reduce_by = current_size.columns - new_size.columns;
-                if let Some(panes_to_resize) = find_reducible_vertical_chain(
-                    &self.panes,
-                    reduce_by,
-                    current_size.columns,
-                    current_size.rows,
-                ) {
-                    self.reduce_panes_left_and_pull_adjacents_left(panes_to_resize, reduce_by);
-                    column_difference = new_size.columns as isize - current_size.columns as isize;
-                    current_size.columns =
-                        (current_size.columns as isize + column_difference) as usize;
-                    successfully_resized = true;
-                };
-            }
-            Ordering::Equal => (),
         }
-        match new_size.rows.cmp(&current_size.rows) {
+        self.solver.reset();
-            Ordering::Greater => {
+        if row_delta != 0 {
-                let increase_by = new_size.rows - current_size.rows;
+            let spans = self.solve_direction(Direction::Vertical, new_size.rows)?;
-                if let Some(panes_to_resize) = find_increasable_horizontal_chain(
+            self.collapse_spans(&spans);
-                    &self.panes,
-                    increase_by,
-                    current_size.columns,
-                    current_size.rows,
-                ) {
-                    self.increase_panes_down_and_push_down_adjacents(panes_to_resize, increase_by);
-                    row_difference = new_size.rows as isize - current_size.rows as isize;
-                    current_size.rows = (current_size.rows as isize + row_difference) as usize;
-                    successfully_resized = true;
-                };
-            }
-            Ordering::Less => {
-                let reduce_by = current_size.rows - new_size.rows;
-                if let Some(panes_to_resize) = find_reducible_horizontal_chain(
-                    &self.panes,
-                    reduce_by,
-                    current_size.columns,
-                    current_size.rows,
-                ) {
-                    self.reduce_panes_up_and_pull_adjacents_up(panes_to_resize, reduce_by);
-                    row_difference = new_size.rows as isize - current_size.rows as isize;
-                    current_size.rows = (current_size.rows as isize + row_difference) as usize;
-                    successfully_resized = true;
-                };
-            }
-            Ordering::Equal => (),
         }
-        if successfully_resized {
+        Some((col_delta, row_delta))
-            Some((column_difference, row_difference))
+    }
+
+    fn solve_direction(&mut self, direction: Direction, space: usize) -> Option<Vec<Span>> {
+        let mut grid = Vec::new();
+        for boundary in self.grid_boundaries(direction) {
+            grid.push(self.spans_in_boundary(direction, boundary));
+        }
+
+        let constraints: Vec<_> = grid
+            .iter()
+            .flat_map(|s| constrain_spans(space, s))
+            .collect();
+
+        // FIXME: This line needs to be restored before merging!
+        //self.solver.add_constraints(&constraints).ok()?;
+        self.solver.add_constraints(&constraints).unwrap();
+        Some(grid.into_iter().flatten().collect())
+    }
+
+    fn grid_boundaries(&self, direction: Direction) -> Vec<(usize, usize)> {
+        // Select the spans running *perpendicular* to the direction of resize
+        let spans: Vec<Span> = self
+            .panes
+            .values()
+            .map(|p| self.get_span(!direction, p.as_ref()))
+            .collect();
+
+        let mut last_edge = 0;
+        let mut bounds = Vec::new();
+        loop {
+            let mut spans_on_edge: Vec<&Span> =
+                spans.iter().filter(|p| p.pos == last_edge).collect();
+            spans_on_edge.sort_unstable_by_key(|s| s.size);
+            if let Some(next) = spans_on_edge.first() {
+                let next_edge = last_edge + next.size;
+                bounds.push((last_edge, next_edge));
+                last_edge = next_edge + GAP_SIZE;
+            } else {
+                break;
+            }
+        }
+        bounds
+    }
+
+    fn spans_in_boundary(&self, direction: Direction, boundary: (usize, usize)) -> Vec<Span> {
+        let (start, end) = boundary;
+        let bwn = |v| start <= v && v < end;
+        let mut spans: Vec<_> = self
+            .panes
+            .values()
+            .filter(|p| {
+                let s = self.get_span(!direction, p.as_ref());
+                bwn(s.pos) || bwn(s.pos + s.size)
+            })
+            .map(|p| self.get_span(direction, p.as_ref()))
+            .collect();
+        spans.sort_unstable_by_key(|s| s.pos);
+        spans
+    }
+
+    fn get_span(&self, direction: Direction, pane: &dyn Pane) -> Span {
+        let pas = pane.position_and_size();
+        let (pos_var, size_var) = self.vars[&pane.pid()];
+        match direction {
+            Direction::Horizontal => Span {
+                pid: pane.pid(),
+                direction,
+                fixed: pas.cols_fixed,
+                pos: pas.x,
+                size: pas.columns,
+                pos_var,
+                size_var,
+            },
+            Direction::Vertical => Span {
+                pid: pane.pid(),
+                direction,
+                fixed: pas.rows_fixed,
+                pos: pas.y,
+                size: pas.rows,
+                pos_var,
+                size_var,
+            },
+        }
+    }
+
+    fn collapse_spans(&mut self, spans: &[Span]) {
+        for span in spans {
+            let solver = &self.solver; // Hand-holding the borrow-checker
+            let pane = self.panes.get_mut(&span.pid).unwrap();
+            let fetch_usize = |v| solver.get_value(v).round() as usize;
+            match span.direction {
+                Direction::Horizontal => pane.change_pos_and_size(&PositionAndSize {
+                    x: fetch_usize(span.pos_var),
+                    columns: fetch_usize(span.size_var),
+                    ..pane.position_and_size()
+                }),
+                Direction::Vertical => pane.change_pos_and_size(&PositionAndSize {
+                    y: fetch_usize(span.pos_var),
+                    rows: fetch_usize(span.size_var),
+                    ..pane.position_and_size()
+                }),
+            }
+            if let PaneId::Terminal(pid) = pane.pid() {
+                self.os_api.set_terminal_size_using_fd(
+                    pid,
+                    pane.columns() as u16,
+                    pane.rows() as u16,
+                );
+            }
+        }
+    }
+}
+
+fn constrain_spans(space: usize, spans: &[Span]) -> HashSet<Constraint> {
+    let mut constraints = HashSet::new();
+
+    // The first span needs to start at 0
+    constraints.insert(spans[0].pos_var | EQ(REQUIRED) | 0.0);
+
+    // Calculating "flexible" space (space not consumed by fixed-size spans)
+    let gap_space = GAP_SIZE * (spans.len() - 1);
+    let old_flex_space = spans
+        .iter()
+        .fold(0, |a, s| if !s.fixed { a + s.size } else { a });
+    let new_flex_space = spans.iter().fold(
+        space - gap_space,
+        |a, s| if s.fixed { a - s.size } else { a },
+    );
+
+    // Keep spans stuck together
+    for pair in spans.windows(2) {
+        let (ls, rs) = (pair[0], pair[1]);
+        constraints
+            .insert((ls.pos_var + ls.size_var + GAP_SIZE as f64) | EQ(REQUIRED) | rs.pos_var);
+    }
+
+    // Try to maintain ratios and lock non-flexible sizes
+    for span in spans {
+        if span.fixed {
+            constraints.insert(span.size_var | EQ(REQUIRED) | span.size as f64);
         } else {
-            None
+            let ratio = span.size as f64 / old_flex_space as f64;
-        }
+            constraints.insert((span.size_var / new_flex_space as f64) | EQ(STRONG) | ratio);
-    }
-    fn reduce_panes_left_and_pull_adjacents_left(
-        &mut self,
-        panes_to_reduce: Vec<PaneId>,
-        reduce_by: usize,
-    ) {
-        let mut pulled_panes: HashSet<PaneId> = HashSet::new();
-        for pane_id in panes_to_reduce {
-            let (pane_x, pane_y, pane_columns, pane_rows) = {
-                let pane = self.panes.get(&pane_id).unwrap();
-                (pane.x(), pane.y(), pane.columns(), pane.rows())
-            };
-            let panes_to_pull = self.panes.values_mut().filter(|p| {
-                p.x() > pane_x + pane_columns
-                    && (p.y() <= pane_y && p.y() + p.rows() >= pane_y
-                        || p.y() >= pane_y && p.y() + p.rows() <= pane_y + pane_rows)
-            });
-            for pane in panes_to_pull {
-                if !pulled_panes.contains(&pane.pid()) {
-                    pane.pull_left(reduce_by);
-                    pulled_panes.insert(pane.pid());
-                }
-            }
-            self.reduce_pane_width_left(&pane_id, reduce_by);
-        }
-    }
-    fn reduce_panes_up_and_pull_adjacents_up(
-        &mut self,
-        panes_to_reduce: Vec<PaneId>,
-        reduce_by: usize,
-    ) {
-        let mut pulled_panes: HashSet<PaneId> = HashSet::new();
-        for pane_id in panes_to_reduce {
-            let (pane_x, pane_y, pane_columns, pane_rows) = {
-                let pane = self.panes.get(&pane_id).unwrap();
-                (pane.x(), pane.y(), pane.columns(), pane.rows())
-            };
-            let panes_to_pull = self.panes.values_mut().filter(|p| {
-                p.y() > pane_y + pane_rows
-                    && (p.x() <= pane_x && p.x() + p.columns() >= pane_x
-                        || p.x() >= pane_x && p.x() + p.columns() <= pane_x + pane_columns)
-            });
-            for pane in panes_to_pull {
-                if !pulled_panes.contains(&pane.pid()) {
-                    pane.pull_up(reduce_by);
-                    pulled_panes.insert(pane.pid());
-                }
-            }
-            self.reduce_pane_height_up(&pane_id, reduce_by);
-        }
-    }
-    fn increase_panes_down_and_push_down_adjacents(
-        &mut self,
-        panes_to_increase: Vec<PaneId>,
-        increase_by: usize,
-    ) {
-        let mut pushed_panes: HashSet<PaneId> = HashSet::new();
-        for pane_id in panes_to_increase {
-            let (pane_x, pane_y, pane_columns, pane_rows) = {
-                let pane = self.panes.get(&pane_id).unwrap();
-                (pane.x(), pane.y(), pane.columns(), pane.rows())
-            };
-            let panes_to_push = self.panes.values_mut().filter(|p| {
-                p.y() > pane_y + pane_rows
-                    && (p.x() <= pane_x && p.x() + p.columns() >= pane_x
-                        || p.x() >= pane_x && p.x() + p.columns() <= pane_x + pane_columns)
-            });
-            for pane in panes_to_push {
-                if !pushed_panes.contains(&pane.pid()) {
-                    pane.push_down(increase_by);
-                    pushed_panes.insert(pane.pid());
-                }
-            }
-            self.increase_pane_height_down(&pane_id, increase_by);
-        }
-    }
-    fn increase_panes_right_and_push_adjacents_right(
-        &mut self,
-        panes_to_increase: Vec<PaneId>,
-        increase_by: usize,
-    ) {
-        let mut pushed_panes: HashSet<PaneId> = HashSet::new();
-        for pane_id in panes_to_increase {
-            let (pane_x, pane_y, pane_columns, pane_rows) = {
-                let pane = self.panes.get(&pane_id).unwrap();
-                (pane.x(), pane.y(), pane.columns(), pane.rows())
-            };
-            let panes_to_push = self.panes.values_mut().filter(|p| {
-                p.x() > pane_x + pane_columns
-                    && (p.y() <= pane_y && p.y() + p.rows() >= pane_y
-                        || p.y() >= pane_y && p.y() + p.rows() <= pane_y + pane_rows)
-            });
-            for pane in panes_to_push {
-                if !pushed_panes.contains(&pane.pid()) {
-                    pane.push_right(increase_by);
-                    pushed_panes.insert(pane.pid());
-                }
-            }
-            self.increase_pane_width_right(&pane_id, increase_by);
-        }
-    }
-    fn reduce_pane_height_up(&mut self, id: &PaneId, count: usize) {
-        let pane = self.panes.get_mut(id).unwrap();
-        pane.reduce_height_up(count);
-        if let PaneId::Terminal(pid) = id {
-            self.os_api
-                .set_terminal_size_using_fd(*pid, pane.columns() as u16, pane.rows() as u16);
-        }
-    }
-    fn increase_pane_height_down(&mut self, id: &PaneId, count: usize) {
-        let pane = self.panes.get_mut(id).unwrap();
-        pane.increase_height_down(count);
-        if let PaneId::Terminal(pid) = pane.pid() {
-            self.os_api
-                .set_terminal_size_using_fd(pid, pane.columns() as u16, pane.rows() as u16);
-        }
-    }
-    fn increase_pane_width_right(&mut self, id: &PaneId, count: usize) {
-        let pane = self.panes.get_mut(id).unwrap();
-        pane.increase_width_right(count);
-        if let PaneId::Terminal(pid) = pane.pid() {
-            self.os_api
-                .set_terminal_size_using_fd(pid, pane.columns() as u16, pane.rows() as u16);
-        }
-    }
-    fn reduce_pane_width_left(&mut self, id: &PaneId, count: usize) {
-        let pane = self.panes.get_mut(id).unwrap();
-        pane.reduce_width_left(count);
-        if let PaneId::Terminal(pid) = pane.pid() {
-            self.os_api
-                .set_terminal_size_using_fd(pid, pane.columns() as u16, pane.rows() as u16);
-        }
-    }
-}
-
-fn find_next_increasable_horizontal_pane(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    right_of: &dyn Pane,
-    increase_by: usize,
-) -> Option<PaneId> {
-    let next_pane_candidates = panes.values().filter(
-        |p| {
-            p.x() == right_of.x() + right_of.columns() + 1 && p.horizontally_overlaps_with(right_of)
-        }, // TODO: the name here is wrong, it should be vertically_overlaps_with
-    );
-    let resizable_candidates =
-        next_pane_candidates.filter(|p| p.can_increase_height_by(increase_by));
-    resizable_candidates.fold(None, |next_pane_id, p| match next_pane_id {
-        Some(next_pane) => {
-            let next_pane = panes.get(&next_pane).unwrap();
-            if next_pane.y() < p.y() {
-                next_pane_id
-            } else {
-                Some(p.pid())
-            }
-        }
-        None => Some(p.pid()),
-    })
-}
-
-fn find_next_increasable_vertical_pane(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    below: &dyn Pane,
-    increase_by: usize,
-) -> Option<PaneId> {
-    let next_pane_candidates = panes.values().filter(
-        |p| p.y() == below.y() + below.rows() + 1 && p.vertically_overlaps_with(below), // TODO: the name here is wrong, it should be horizontally_overlaps_with
-    );
-    let resizable_candidates =
-        next_pane_candidates.filter(|p| p.can_increase_width_by(increase_by));
-    resizable_candidates.fold(None, |next_pane_id, p| match next_pane_id {
-        Some(next_pane) => {
-            let next_pane = panes.get(&next_pane).unwrap();
-            if next_pane.x() < p.x() {
-                next_pane_id
-            } else {
-                Some(p.pid())
-            }
-        }
-        None => Some(p.pid()),
-    })
-}
-
-fn find_next_reducible_vertical_pane(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    below: &dyn Pane,
-    reduce_by: usize,
-) -> Option<PaneId> {
-    let next_pane_candidates = panes.values().filter(
-        |p| p.y() == below.y() + below.rows() + 1 && p.vertically_overlaps_with(below), // TODO: the name here is wrong, it should be horizontally_overlaps_with
-    );
-    let resizable_candidates = next_pane_candidates.filter(|p| p.can_reduce_width_by(reduce_by));
-    resizable_candidates.fold(None, |next_pane_id, p| match next_pane_id {
-        Some(next_pane) => {
-            let next_pane = panes.get(&next_pane).unwrap();
-            if next_pane.x() < p.x() {
-                next_pane_id
-            } else {
-                Some(p.pid())
-            }
-        }
-        None => Some(p.pid()),
-    })
-}
-
-fn find_next_reducible_horizontal_pane(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    right_of: &dyn Pane,
-    reduce_by: usize,
-) -> Option<PaneId> {
-    let next_pane_candidates = panes.values().filter(
-        |p| {
-            p.x() == right_of.x() + right_of.columns() + 1 && p.horizontally_overlaps_with(right_of)
-        }, // TODO: the name here is wrong, it should be vertically_overlaps_with
-    );
-    let resizable_candidates = next_pane_candidates.filter(|p| p.can_reduce_height_by(reduce_by));
-    resizable_candidates.fold(None, |next_pane_id, p| match next_pane_id {
-        Some(next_pane) => {
-            let next_pane = panes.get(&next_pane).unwrap();
-            if next_pane.y() < p.y() {
-                next_pane_id
-            } else {
-                Some(p.pid())
-            }
-        }
-        None => Some(p.pid()),
-    })
-}
-
-fn find_increasable_horizontal_chain(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    increase_by: usize,
-    screen_width: usize,
-    screen_height: usize, // TODO: this is the previous size (make this clearer)
-) -> Option<Vec<PaneId>> {
-    let mut horizontal_coordinate = 0;
-    loop {
-        if horizontal_coordinate == screen_height {
-            return None;
-        }
-
-        match panes
-            .values()
-            .find(|p| p.x() == 0 && p.y() == horizontal_coordinate)
-        {
-            Some(leftmost_pane) => {
-                if !leftmost_pane.can_increase_height_by(increase_by) {
-                    horizontal_coordinate = leftmost_pane.y() + leftmost_pane.rows() + 1;
-                    continue;
-                }
-                let mut panes_to_resize = vec![];
-                let mut current_pane = leftmost_pane;
-                loop {
-                    panes_to_resize.push(current_pane.pid());
-                    if current_pane.x() + current_pane.columns() == screen_width {
-                        return Some(panes_to_resize);
-                    }
-                    match find_next_increasable_horizontal_pane(
-                        panes,
-                        current_pane.as_ref(),
-                        increase_by,
-                    ) {
-                        Some(next_pane_id) => {
-                            current_pane = panes.get(&next_pane_id).unwrap();
-                        }
-                        None => {
-                            horizontal_coordinate = leftmost_pane.y() + leftmost_pane.rows() + 1;
-                            break;
-                        }
-                    };
-                }
-            }
-            None => {
-                return None;
-            }
-        }
-    }
-}
-
-fn find_increasable_vertical_chain(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    increase_by: usize,
-    screen_width: usize,
-    screen_height: usize, // TODO: this is the previous size (make this clearer)
-) -> Option<Vec<PaneId>> {
-    let mut vertical_coordinate = 0;
-    loop {
-        if vertical_coordinate == screen_width {
-            return None;
-        }
-
-        match panes
-            .values()
-            .find(|p| p.y() == 0 && p.x() == vertical_coordinate)
-        {
-            Some(topmost_pane) => {
-                if !topmost_pane.can_increase_width_by(increase_by) {
-                    vertical_coordinate = topmost_pane.x() + topmost_pane.columns() + 1;
-                    continue;
-                }
-                let mut panes_to_resize = vec![];
-                let mut current_pane = topmost_pane;
-                loop {
-                    panes_to_resize.push(current_pane.pid());
-                    if current_pane.y() + current_pane.rows() == screen_height {
-                        return Some(panes_to_resize);
-                    }
-                    match find_next_increasable_vertical_pane(
-                        panes,
-                        current_pane.as_ref(),
-                        increase_by,
-                    ) {
-                        Some(next_pane_id) => {
-                            current_pane = panes.get(&next_pane_id).unwrap();
-                        }
-                        None => {
-                            vertical_coordinate = topmost_pane.x() + topmost_pane.columns() + 1;
-                            break;
-                        }
-                    };
-                }
-            }
-            None => {
-                return None;
-            }
-        }
-    }
-}
-
-fn find_reducible_horizontal_chain(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    reduce_by: usize,
-    screen_width: usize,
-    screen_height: usize, // TODO: this is the previous size (make this clearer)
-) -> Option<Vec<PaneId>> {
-    let mut horizontal_coordinate = 0;
-    loop {
-        if horizontal_coordinate == screen_height {
-            return None;
-        }
-
-        match panes
-            .values()
-            .find(|p| p.x() == 0 && p.y() == horizontal_coordinate)
-        {
-            Some(leftmost_pane) => {
-                if !leftmost_pane.can_reduce_height_by(reduce_by) {
-                    horizontal_coordinate = leftmost_pane.y() + leftmost_pane.rows() + 1;
-                    continue;
-                }
-                let mut panes_to_resize = vec![];
-                let mut current_pane = leftmost_pane;
-                loop {
-                    panes_to_resize.push(current_pane.pid());
-                    if current_pane.x() + current_pane.columns() == screen_width {
-                        return Some(panes_to_resize);
-                    }
-                    match find_next_reducible_horizontal_pane(
-                        panes,
-                        current_pane.as_ref(),
-                        reduce_by,
-                    ) {
-                        Some(next_pane_id) => {
-                            current_pane = panes.get(&next_pane_id).unwrap();
-                        }
-                        None => {
-                            horizontal_coordinate = leftmost_pane.y() + leftmost_pane.rows() + 1;
-                            break;
-                        }
-                    };
-                }
-            }
-            None => {
-                return None;
-            }
-        }
-    }
-}
-
-fn find_reducible_vertical_chain(
-    panes: &BTreeMap<PaneId, Box<dyn Pane>>,
-    increase_by: usize,
-    screen_width: usize,
-    screen_height: usize, // TODO: this is the previous size (make this clearer)
-) -> Option<Vec<PaneId>> {
-    let mut vertical_coordinate = 0;
-    loop {
-        if vertical_coordinate == screen_width {
-            return None;
-        }
-
-        match panes
-            .values()
-            .find(|p| p.y() == 0 && p.x() == vertical_coordinate)
-        {
-            Some(topmost_pane) => {
-                if !topmost_pane.can_reduce_width_by(increase_by) {
-                    vertical_coordinate = topmost_pane.x() + topmost_pane.columns() + 1;
-                    continue;
-                }
-                let mut panes_to_resize = vec![];
-                let mut current_pane = topmost_pane;
-                loop {
-                    panes_to_resize.push(current_pane.pid());
-                    if current_pane.y() + current_pane.rows() == screen_height {
-                        return Some(panes_to_resize);
-                    }
-                    match find_next_reducible_vertical_pane(
-                        panes,
-                        current_pane.as_ref(),
-                        increase_by,
-                    ) {
-                        Some(next_pane_id) => {
-                            current_pane = panes.get(&next_pane_id).unwrap();
-                        }
-                        None => {
-                            vertical_coordinate = topmost_pane.x() + topmost_pane.columns() + 1;
-                            break;
-                        }
-                    };
-                }
-            }
-            None => {
-                return None;
-            }
         }
     }
+
+    // The last pane needs to end at the end of the space
+    let last = spans.last().unwrap();
+    constraints.insert((last.pos_var + last.size_var) | EQ(REQUIRED) | space as f64);
+
+    constraints
 }

zellij-server/src/wasm_vm.rs

@@ -158,7 +158,8 @@ pub(crate) fn zellij_exports(store: &Store, plugin_env: &PluginEnv) -> ImportObj
         host_subscribe,
         host_unsubscribe,
         host_set_invisible_borders,
-        host_set_max_height,
+        host_set_fixed_height,
+        host_set_fixed_width,
         host_set_selectable,
         host_get_plugin_ids,
         host_open_file,
@@ -189,13 +190,24 @@ fn host_set_selectable(plugin_env: &PluginEnv, selectable: i32) {
         .unwrap()
 }
 
-fn host_set_max_height(plugin_env: &PluginEnv, max_height: i32) {
+fn host_set_fixed_height(plugin_env: &PluginEnv, fixed_height: i32) {
-    let max_height = max_height as usize;
+    let fixed_height = fixed_height as usize;
     plugin_env
         .senders
-        .send_to_screen(ScreenInstruction::SetMaxHeight(
+        .send_to_screen(ScreenInstruction::SetFixedHeight(
             PaneId::Plugin(plugin_env.plugin_id),
-            max_height,
+            fixed_height,
+        ))
+        .unwrap()
+}
+
+fn host_set_fixed_width(plugin_env: &PluginEnv, fixed_width: i32) {
+    let fixed_width = fixed_width as usize;
+    plugin_env
+        .senders
+        .send_to_screen(ScreenInstruction::SetFixedWidth(
+            PaneId::Plugin(plugin_env.plugin_id),
+            fixed_width,
         ))
         .unwrap()
 }

zellij-tile/src/shim.rs

@@ -17,8 +17,12 @@ pub fn unsubscribe(event_types: &[EventType]) {
 
 // Plugin Settings
 
-pub fn set_max_height(max_height: i32) {
+pub fn set_fixed_height(fixed_height: i32) {
-    unsafe { host_set_max_height(max_height) };
+    unsafe { host_set_fixed_height(fixed_height) };
+}
+
+pub fn set_fixed_width(fixed_width: i32) {
+    unsafe { host_set_fixed_width(fixed_width) };
 }
 
 pub fn set_selectable(selectable: bool) {
@@ -64,7 +68,8 @@ pub fn object_to_stdout(object: &impl Serialize) {
 extern "C" {
     fn host_subscribe();
     fn host_unsubscribe();
-    fn host_set_max_height(max_height: i32);
+    fn host_set_fixed_height(fixed_height: i32);
+    fn host_set_fixed_width(fixed_width: i32);
     fn host_set_selectable(selectable: i32);
     fn host_set_invisible_borders(invisible_borders: i32);
     fn host_get_plugin_ids();

zellij-utils/src/errors.rs

@@ -207,7 +207,8 @@ pub enum ScreenContext {
     ToggleActiveTerminalFullscreen,
     SetSelectable,
     SetInvisibleBorders,
-    SetMaxHeight,
+    SetFixedHeight,
+    SetFixedWidth,
     ClosePane,
     ApplyLayout,
     NewTab,

zellij-utils/src/pane_size.rs

@@ -9,8 +9,11 @@ pub struct PositionAndSize {
     pub y: usize,
     pub rows: usize,
     pub columns: usize,
-    pub max_rows: Option<usize>,
+    // FIXME: Honestly, these shouldn't exist and rows / columns should be enums like:
-    pub max_columns: Option<usize>,
+    // Dimension::Flex(usize) / Dimension::Fixed(usize), but 400+ compiler errors is more than
+    // I'm in the mood for right now...
+    pub rows_fixed: bool,
+    pub cols_fixed: bool,
 }
 
 impl From<Winsize> for PositionAndSize {