feat: add responsive ultrawide work lanes

crates/lumbridge-terminal/src/lib.rs

@@ -7,7 +7,7 @@
 #![forbid(unsafe_code)]
 
 use alacritty_terminal::event::{Event, EventListener, WindowSize};
-use alacritty_terminal::grid::Dimensions;
+use alacritty_terminal::grid::{Dimensions, Scroll};
 use alacritty_terminal::term::cell::Flags;
 use alacritty_terminal::term::{Config, Osc52, Term, TermMode, point_to_viewport};
 use alacritty_terminal::vte::ansi::{Color, CursorShape, NamedColor, Processor};
@@ -259,12 +259,23 @@ impl TerminalModes {
 pub struct TerminalSnapshot {
     pub revision: u64,
     pub dimensions: TerminalDimensions,
+    pub display_offset: usize,
     pub cells: Vec<TerminalCell>,
     pub cursor: TerminalCursor,
     pub modes: TerminalModes,
     pub title: Option<String>,
 }
 
+/// Framework-neutral movement through the retained terminal history.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum TerminalScroll {
+    Delta(i32),
+    PageUp,
+    PageDown,
+    Top,
+    Bottom,
+}
+
 impl TerminalSnapshot {
     #[must_use]
     pub fn cell(&self, row: u16, column: u16) -> Option<&TerminalCell> {
@@ -544,6 +555,31 @@ impl TerminalEngine {
         }
     }
 
+    /// Moves the visible viewport without writing bytes to the child PTY.
+    ///
+    /// Returns `true` only when the retained-history offset changed.
+    pub fn scroll_display(&mut self, scroll: TerminalScroll) -> bool {
+        let previous_offset = self.terminal.grid().display_offset();
+        let scroll = match scroll {
+            TerminalScroll::Delta(lines) => Scroll::Delta(lines),
+            TerminalScroll::PageUp => Scroll::PageUp,
+            TerminalScroll::PageDown => Scroll::PageDown,
+            TerminalScroll::Top => Scroll::Top,
+            TerminalScroll::Bottom => Scroll::Bottom,
+        };
+        self.terminal.scroll_display(scroll);
+        if self.terminal.grid().display_offset() == previous_offset {
+            return false;
+        }
+        self.revision = self.revision.saturating_add(1);
+        true
+    }
+
+    #[must_use]
+    pub fn display_offset(&self) -> usize {
+        self.terminal.grid().display_offset()
+    }
+
     #[must_use]
     pub fn snapshot(&self) -> TerminalSnapshot {
         let renderable = self.terminal.renderable_content();
@@ -571,6 +607,7 @@ impl TerminalEngine {
         TerminalSnapshot {
             revision: self.revision,
             dimensions: self.dimensions,
+            display_offset: renderable.display_offset,
             cells,
             cursor: TerminalCursor {
                 row: u16::try_from(cursor_point.line).unwrap_or(u16::MAX),
@@ -874,6 +911,7 @@ mod tests {
     use super::{
         KeyModifiers, TerminalCellStyle, TerminalDimensions, TerminalEngine, TerminalEngineOptions,
         TerminalEvent, TerminalKey, TerminalKeyEvent, TerminalModes, TerminalNamedColor,
+        TerminalScroll,
     };
 
     fn engine(rows: u16, columns: u16) -> TerminalEngine {
@@ -917,6 +955,23 @@ mod tests {
         assert_eq!(engine.snapshot().plain_rows()[0], "primary");
     }
 
+    #[test]
+    fn scrolls_retained_history_without_touching_the_pty_input_path() {
+        let mut engine = engine(2, 8);
+        engine.process(b"one\r\ntwo\r\nthree\r\nfour");
+        assert_eq!(engine.display_offset(), 0);
+
+        let revision = engine.revision();
+        assert!(engine.scroll_display(TerminalScroll::PageUp));
+        assert!(engine.display_offset() > 0);
+        assert!(engine.revision() > revision);
+        assert_eq!(engine.snapshot().display_offset, engine.display_offset());
+
+        assert!(engine.scroll_display(TerminalScroll::Bottom));
+        assert_eq!(engine.display_offset(), 0);
+        assert!(!engine.scroll_display(TerminalScroll::Bottom));
+    }
+
     #[test]
     fn emits_protocol_replies_without_logging_input_content() {
         let mut engine = engine(4, 10);