perf(ui): avoid full pane mode reads for scrollbars (#2554)

4 files changed, 19 insertions, 4 deletions

diff --git a/src/pane.rs b/src/pane.rs
index da99f55e..b2c01f01 100644
--- a/src/pane.rs
+++ b/src/pane.rs
@@ -2596,6 +2596,10 @@ impl PaneRuntime {
         self.terminal.input_state()
     }
 
+    pub fn alternate_screen_active(&self) -> bool {
+        self.terminal.alternate_screen_active()
+    }
+
     pub fn cursor_state(&self, area: Rect, show_cursor: bool) -> Option<TerminalCursorState> {
         if !show_cursor {
             return None;
diff --git a/src/pane/terminal.rs b/src/pane/terminal.rs
index a6e5c1da..1c10726c 100644
--- a/src/pane/terminal.rs
+++ b/src/pane/terminal.rs
@@ -388,6 +388,10 @@ impl PaneTerminal {
         self.ghostty.input_state()
     }
 
+    pub fn alternate_screen_active(&self) -> bool {
+        self.ghostty.alternate_screen_active()
+    }
+
     pub fn wheel_routing(&self) -> Option<crate::pane::WheelRouting> {
         self.ghostty.wheel_routing()
     }
@@ -1665,6 +1669,12 @@ impl GhosttyPaneTerminal {
         core.kitty_keyboard.replay_ansi()
     }
 
+    pub fn alternate_screen_active(&self) -> bool {
+        self.core.lock().is_ok_and(|core| {
+            core.terminal.active_screen().ok() == Some(crate::ghostty::ActiveScreen::Alternate)
+        })
+    }
+
     pub fn input_state(&self) -> Option<InputState> {
         let Ok(core) = self.core.lock() else {
             return None;
diff --git a/src/terminal/runtime.rs b/src/terminal/runtime.rs
index 13e29690..d3900b68 100644
--- a/src/terminal/runtime.rs
+++ b/src/terminal/runtime.rs
@@ -315,6 +315,10 @@ impl TerminalRuntime {
         self.0.input_state()
     }
 
+    pub fn alternate_screen_active(&self) -> bool {
+        self.0.alternate_screen_active()
+    }
+
     pub fn cursor_state(
         &self,
         area: Rect,
diff --git a/src/ui/panes.rs b/src/ui/panes.rs
index df9813cf..cce8ab02 100644
--- a/src/ui/panes.rs
+++ b/src/ui/panes.rs
@@ -32,10 +32,7 @@ fn pane_border_title(label: &str, pane_width: u16, _focused: bool) -> Option<Str
 }
 
 fn terminal_inner_rect(rt: &TerminalRuntime, pane_inner: Rect, pane_scrollbars: bool) -> Rect {
-    if !pane_scrollbars
-        || pane_inner.width <= 4
-        || rt.input_state().is_some_and(|state| state.alternate_screen)
-    {
+    if !pane_scrollbars || pane_inner.width <= 4 || rt.alternate_screen_active() {
         return pane_inner;
     }