grid: scrollback with mouse-wheel and Shift+PageUp scrolling

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I12b2ed33a705eb3474a7d14a295e021d6a6a6964

src/grid.rs

@@ -1,8 +1,13 @@
 //! The terminal screen: a grid of styled cells, a cursor, and the editing
 //! operations the VT parser drives.
 
+use std::collections::VecDeque;
+
 use unicode_width::UnicodeWidthChar;
 
+/// Maximum scrollback lines retained for the main screen.
+const SCROLLBACK_CAP: usize = 10_000;
+
 /// A cell colour: terminal default, a palette index, or direct RGB.
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
 pub enum Color {
@@ -122,6 +127,10 @@ pub struct Grid {
     tabs: Vec<bool>,
     /// Saved primary screen while the alternate screen is active.
     alt_saved: Option<Vec<Vec<Cell>>>,
+    /// Lines that have scrolled off the top of the main screen, newest last.
+    scrollback: VecDeque<Vec<Cell>>,
+    /// How many lines the viewport is scrolled back from the live bottom.
+    view_offset: usize,
     cursor_shape: CursorShape,
     cursor_visible: bool,
     /// Application cursor-keys mode (DECCKM): arrows send SS3 instead of CSI.
@@ -153,6 +162,8 @@ impl Grid {
             wrap_pending: false,
             tabs: default_tabs(cols),
             alt_saved: None,
+            scrollback: VecDeque::new(),
+            view_offset: 0,
             cursor_shape: CursorShape::default(),
             cursor_visible: true,
             cursor_color: None,
@@ -184,6 +195,9 @@ impl Grid {
         self.cursor.x = self.cursor.x.min(cols - 1);
         self.cursor.y = self.cursor.y.min(rows - 1);
         self.wrap_pending = false;
+        // Scrollback lines keep their old width (no reflow); snap to the live
+        // screen so the viewport never indexes a stale-width line.
+        self.view_offset = 0;
     }
 
     pub fn cursor(&self) -> (usize, usize) {
@@ -475,6 +489,21 @@ impl Grid {
 
     pub fn scroll_up(&mut self, n: usize) {
         let n = n.min(self.bottom - self.top + 1);
+        // Lines leaving the top of the *whole* main screen become scrollback;
+        // a DECSTBM region scroll (top > 0) or the alt screen does not.
+        if self.top == 0 && self.alt_saved.is_none() {
+            for y in 0..n {
+                let line = std::mem::replace(&mut self.lines[y], vec![Cell::default(); self.cols]);
+                self.scrollback.push_back(line);
+            }
+            while self.scrollback.len() > SCROLLBACK_CAP {
+                self.scrollback.pop_front();
+            }
+            // Keep a scrolled-back viewport anchored to the same content.
+            if self.view_offset > 0 {
+                self.view_offset = (self.view_offset + n).min(self.scrollback.len());
+            }
+        }
         for y in self.top..=self.bottom {
             if y + n <= self.bottom {
                 self.lines.swap(y, y + n);
@@ -618,6 +647,7 @@ impl Grid {
         if self.alt_saved.is_some() {
             return;
         }
+        self.view_offset = 0;
         let blank = vec![vec![Cell::default(); self.cols]; self.rows];
         self.alt_saved = Some(std::mem::replace(&mut self.lines, blank));
     }
@@ -628,6 +658,45 @@ impl Grid {
         }
     }
 
+    // --- scrollback viewport ---
+
+    /// Scroll the viewport by `delta` lines: positive = back into history,
+    /// negative = toward the live screen. No-op on the alternate screen.
+    pub fn scroll_view(&mut self, delta: isize) {
+        if self.alt_saved.is_some() {
+            return;
+        }
+        let max = self.scrollback.len() as isize;
+        self.view_offset = (self.view_offset as isize + delta).clamp(0, max) as usize;
+    }
+
+    pub fn scroll_to_bottom(&mut self) {
+        self.view_offset = 0;
+    }
+
+    /// Whether the viewport is showing the live screen (not scrolled back).
+    pub fn view_at_bottom(&self) -> bool {
+        self.view_offset == 0
+    }
+
+    /// One page (a screenful) of lines, for page-scroll bindings.
+    pub fn page(&self) -> usize {
+        self.rows.max(1)
+    }
+
+    /// The cells shown at viewport row `y` (0 = top of the window), accounting
+    /// for the scrollback offset. May differ from `cols` in width if the line
+    /// predates a resize (no reflow yet), so callers must not assume length.
+    pub fn view_row(&self, y: usize) -> &[Cell] {
+        let start = self.scrollback.len() - self.view_offset;
+        let idx = start + y;
+        if idx < self.scrollback.len() {
+            &self.scrollback[idx]
+        } else {
+            &self.lines[idx - self.scrollback.len()]
+        }
+    }
+
     // --- inspection (logging + tests) ---
 
     /// The visible text of one row, trailing blanks trimmed.
@@ -713,6 +782,25 @@ mod tests {
         assert_eq!(g.row_text(0), "a  def");
     }
 
+    #[test]
+    fn scrollback_captures_scrolled_lines() {
+        let mut g = Grid::new(8, 2);
+        for c in ['1', '2', '3'] {
+            g.print(c);
+            g.next_line();
+        }
+        // Live screen: newest line on top, cleared line below.
+        assert_eq!(g.view_row(0)[0].c, '3');
+        assert!(g.view_at_bottom());
+        // Scroll back to reveal the two captured lines.
+        g.scroll_view(2);
+        assert!(!g.view_at_bottom());
+        assert_eq!(g.view_row(0)[0].c, '1');
+        assert_eq!(g.view_row(1)[0].c, '2');
+        g.scroll_to_bottom();
+        assert_eq!(g.view_row(0)[0].c, '3');
+    }
+
     #[test]
     fn wide_char_occupies_two_columns() {
         let mut g = Grid::new(6, 1);

src/render.rs

@@ -126,12 +126,14 @@ impl Renderer {
         canvas.clear(DEFAULT_BG);
 
         let m = self.fonts.metrics();
+        let cols = grid.cols();
 
         // Cell backgrounds: only paint cells that differ from the cleared
-        // default - most of a screen is default background.
+        // default - most of a screen is default background. Rows come through
+        // the scrollback viewport and may be shorter than `cols` after a resize.
         for y in 0..grid.rows() {
-            for x in 0..grid.cols() {
+            for (x, cell) in grid.view_row(y).iter().take(cols).enumerate() {
-                let (_, bg) = cell_colors(grid.cell(x, y));
+                let (_, bg) = cell_colors(cell);
                 if bg != DEFAULT_BG {
                     let (px, py) = (x as i32 * m.width as i32, y as i32 * m.height as i32);
                     canvas.fill_rect(px, py, m.width, m.height, bg);
@@ -140,8 +142,7 @@ impl Renderer {
         }
 
         for y in 0..grid.rows() {
-            for x in 0..grid.cols() {
+            for (x, cell) in grid.view_row(y).iter().take(cols).enumerate() {
-                let cell = grid.cell(x, y);
                 if cell.flags.contains(Flags::WIDE_CONT) {
                     continue;
                 }
@@ -162,7 +163,10 @@ impl Renderer {
             }
         }
 
-        self.draw_cursor(&mut canvas, grid, m, focused);
+        // The cursor belongs to the live screen; hide it while scrolled back.
+        if grid.view_at_bottom() {
+            self.draw_cursor(&mut canvas, grid, m, focused);
+        }
     }
 
     /// Draw the cursor: a solid block/underline/beam when focused, a hollow

src/vt.rs

@@ -123,6 +123,19 @@ impl Term {
         self.grid.resize(cols, rows);
     }
 
+    pub fn scroll_view(&mut self, delta: isize) {
+        self.grid.scroll_view(delta);
+    }
+
+    pub fn scroll_to_bottom(&mut self) {
+        self.grid.scroll_to_bottom();
+    }
+
+    /// Lines per page, for page-scroll bindings.
+    pub fn page(&self) -> usize {
+        self.grid.page()
+    }
+
     pub fn title(&self) -> Option<&str> {
         self.title.as_deref()
     }

src/wayland.rs

@@ -18,14 +18,15 @@ use crate::render::Renderer;
 use crate::vt::Term;
 use smithay_client_toolkit::{
     compositor::{CompositorHandler, CompositorState},
-    delegate_compositor, delegate_keyboard, delegate_output, delegate_registry, delegate_seat,
+    delegate_compositor, delegate_keyboard, delegate_output, delegate_pointer, delegate_registry,
-    delegate_shm, delegate_xdg_shell, delegate_xdg_window,
+    delegate_seat, delegate_shm, delegate_xdg_shell, delegate_xdg_window,
     output::{OutputHandler, OutputState},
     registry::{ProvidesRegistryState, RegistryState},
     registry_handlers,
     seat::{
         Capability, SeatHandler, SeatState,
         keyboard::{KeyEvent, KeyboardHandler, Keysym, Modifiers, RawModifiers, RepeatInfo},
+        pointer::{PointerEvent, PointerEventKind, PointerHandler},
     },
     shell::{
         WaylandSurface,
@@ -39,7 +40,7 @@ use smithay_client_toolkit::{
 use wayland_client::{
     Connection, QueueHandle,
     globals::registry_queue_init,
-    protocol::{wl_keyboard, wl_output, wl_seat, wl_shm, wl_surface},
+    protocol::{wl_keyboard, wl_output, wl_pointer, wl_seat, wl_shm, wl_surface},
 };
 
 /// Default window size in pixels before the compositor suggests one.
@@ -90,6 +91,7 @@ pub fn run() -> anyhow::Result<ExitCode> {
         renderer,
         loop_handle: event_loop.handle(),
         keyboard: None,
+        pointer: None,
         modifiers: Modifiers::default(),
         // The PTY is spawned on the first configure, once the real window size
         // is known, so the shell starts at the final size and is not hit by a
@@ -158,6 +160,7 @@ struct App {
     renderer: Renderer,
     loop_handle: LoopHandle<'static, App>,
     keyboard: Option<wl_keyboard::WlKeyboard>,
+    pointer: Option<wl_pointer::WlPointer>,
     modifiers: Modifiers,
     /// `None` until the first configure spawns the shell.
     session: Option<Session>,
@@ -233,17 +236,36 @@ impl App {
         });
     }
 
-    /// Encode a key event and write it to the shell.
+    /// Handle a key (initial press or repeat): Shift+PageUp/PageDown scroll the
-    fn send_key(&self, event: &KeyEvent) {
+    /// viewport locally; anything else is encoded to the shell and snaps the
+    /// viewport back to the live screen.
+    fn handle_key(&mut self, event: &KeyEvent) {
+        if self.modifiers.shift && matches!(event.keysym, Keysym::Page_Up | Keysym::Page_Down) {
+            if let Some(session) = self.session.as_mut() {
+                let page = session.term.page() as isize;
+                let delta = if event.keysym == Keysym::Page_Up {
+                    page
+                } else {
+                    -page
+                };
+                session.term.scroll_view(delta);
+                self.dirty = true;
+            }
+            return;
+        }
+
         let app_cursor = self
             .session
             .as_ref()
             .is_some_and(|s| s.term.grid().app_cursor());
         if let Some(bytes) = crate::input::encode(event, self.modifiers, app_cursor)
-            && let Some(session) = self.session.as_ref()
+            && let Some(session) = self.session.as_mut()
-            && let Err(err) = write_all(session.pty.master(), &bytes)
         {
-            tracing::warn!("write key to pty: {err}");
+            session.term.scroll_to_bottom();
+            self.dirty = true;
+            if let Err(err) = write_all(session.pty.master(), &bytes) {
+                tracing::warn!("write key to pty: {err}");
+            }
         }
     }
 
@@ -439,13 +461,19 @@ impl SeatHandler for App {
                 &seat,
                 None,
                 loop_handle,
-                Box::new(|app: &mut App, _kbd, event| app.send_key(&event)),
+                Box::new(|app: &mut App, _kbd, event| app.handle_key(&event)),
             );
             match keyboard {
                 Ok(keyboard) => self.keyboard = Some(keyboard),
                 Err(err) => tracing::warn!("get keyboard: {err}"),
             }
         }
+        if capability == Capability::Pointer && self.pointer.is_none() {
+            match self.seat_state.get_pointer(qh, &seat) {
+                Ok(pointer) => self.pointer = Some(pointer),
+                Err(err) => tracing::warn!("get pointer: {err}"),
+            }
+        }
     }
 
     fn remove_capability(
@@ -455,10 +483,18 @@ impl SeatHandler for App {
         _: wl_seat::WlSeat,
         capability: Capability,
     ) {
-        if capability == Capability::Keyboard
+        match capability {
-            && let Some(keyboard) = self.keyboard.take()
+            Capability::Keyboard => {
-        {
+                if let Some(keyboard) = self.keyboard.take() {
-            keyboard.release();
+                    keyboard.release();
+                }
+            }
+            Capability::Pointer => {
+                if let Some(pointer) = self.pointer.take() {
+                    pointer.release();
+                }
+            }
+            _ => {}
         }
     }
 
@@ -500,7 +536,7 @@ impl KeyboardHandler for App {
         _: u32,
         event: KeyEvent,
     ) {
-        self.send_key(&event);
+        self.handle_key(&event);
     }
 
     fn repeat_key(
@@ -548,6 +584,45 @@ impl KeyboardHandler for App {
     }
 }
 
+impl PointerHandler for App {
+    fn pointer_frame(
+        &mut self,
+        _: &Connection,
+        _: &QueueHandle<Self>,
+        _: &wl_pointer::WlPointer,
+        events: &[PointerEvent],
+    ) {
+        let cell_h = f64::from(self.renderer.metrics().height);
+        for event in events {
+            let PointerEventKind::Axis { vertical, .. } = &event.kind else {
+                continue;
+            };
+            // Wheel notches arrive as value120 (÷120) or legacy discrete steps,
+            // ~3 lines each; touchpads send pixels, mapped per cell height.
+            let (raw, scale) = if vertical.value120 != 0 {
+                (f64::from(vertical.value120) / 120.0, 3.0)
+            } else if vertical.discrete != 0 {
+                (f64::from(vertical.discrete), 3.0)
+            } else if cell_h > 0.0 {
+                (vertical.absolute / cell_h, 1.0)
+            } else {
+                continue;
+            };
+            if raw == 0.0 {
+                continue;
+            }
+            // Positive axis = scroll down (toward live); we scroll the viewport
+            // the opposite way (negative offset delta).
+            let lines = (raw.abs() * scale).ceil().max(1.0) as isize;
+            let delta = if raw < 0.0 { lines } else { -lines };
+            if let Some(session) = self.session.as_mut() {
+                session.term.scroll_view(delta);
+                self.dirty = true;
+            }
+        }
+    }
+}
+
 impl OutputHandler for App {
     fn output_state(&mut self) -> &mut OutputState {
         &mut self.output_state
@@ -572,6 +647,7 @@ delegate_output!(App);
 delegate_shm!(App);
 delegate_seat!(App);
 delegate_keyboard!(App);
+delegate_pointer!(App);
 delegate_xdg_shell!(App);
 delegate_xdg_window!(App);
 delegate_registry!(App);