delay allocation of the alternate screen

3 files changed, 23 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 404671f..75c5e60 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## [Unreleased]
+
+## Changed
+
+* Delay allocation of the alternate screen until it is used (saves a bit of
+  memory in basic cases)
+
 ## [0.13.1] - 2021-12-04
 
 ## Fixed
diff --git a/src/grid.rs b/src/grid.rs
index 246e9e6..9681638 100644
--- a/src/grid.rs
+++ b/src/grid.rs
@@ -21,7 +21,7 @@ impl Grid {
             size,
             pos: Pos::default(),
             saved_pos: Pos::default(),
-            rows: vec![crate::row::Row::new(size.cols); size.rows as usize],
+            rows: vec![],
             scroll_top: 0,
             scroll_bottom: size.rows - 1,
             origin_mode: false,
@@ -32,6 +32,17 @@ impl Grid {
         }
     }
 
+    pub fn allocate_rows(&mut self) {
+        if self.rows.is_empty() {
+            self.rows.extend(
+                std::iter::repeat_with(|| {
+                    crate::row::Row::new(self.size.cols)
+                })
+                .take(self.size.rows as usize),
+            );
+        }
+    }
+
     fn new_row(&self) -> crate::row::Row {
         crate::row::Row::new(self.size.cols)
     }
diff --git a/src/screen.rs b/src/screen.rs
index 74e0559..ae6bd2d 100644
--- a/src/screen.rs
+++ b/src/screen.rs
@@ -85,8 +85,10 @@ impl Screen {
         size: crate::grid::Size,
         scrollback_len: usize,
     ) -> Self {
+        let mut grid = crate::grid::Grid::new(size, scrollback_len);
+        grid.allocate_rows();
         Self {
-            grid: crate::grid::Grid::new(size, scrollback_len),
+            grid,
             alternate_grid: crate::grid::Grid::new(size, 0),
 
             attrs: crate::attrs::Attrs::default(),
@@ -759,6 +761,7 @@ impl Screen {
     fn enter_alternate_grid(&mut self) {
         self.grid_mut().set_scrollback(0);
         self.set_mode(MODE_ALTERNATE_SCREEN);
+        self.alternate_grid.allocate_rows();
     }
 
     fn exit_alternate_grid(&mut self) {