Fix deletion of lines when clearing the screen

Previously Alacritty would delete lines when clearing the screen, leading to a
loss of data in the scrollback buffer. Instead of deleting these lines, they
are now rotated outside of the visible region.

This also fixes some issues with Alacritty only resetting lines partially when
the background color of the template cell changed.

Fixes #2199.

1 files changed, 20 insertions, 12 deletions

diff --git a/alacritty_terminal/src/term/mod.rs b/alacritty_terminal/src/term/mod.rs
index 8d69fb3b..6a51ba35 100644
--- a/alacritty_terminal/src/term/mod.rs
+++ b/alacritty_terminal/src/term/mod.rs
@@ -701,7 +701,9 @@ pub struct Term<T> {
     /// Mode flags
     mode: TermMode,
 
-    /// Scroll region
+    /// Scroll region.
+    ///
+    /// Range going from top to bottom of the terminal, indexed from the top of the viewport.
     scroll_region: Range<Line>,
 
     pub dirty: bool,
@@ -1749,17 +1751,6 @@ impl<T: EventListener> ansi::Handler for Term<T> {
         self.grid.selection = None;
 
         match mode {
-            ansi::ClearMode::Below => {
-                for cell in &mut self.grid[self.cursor.point.line][self.cursor.point.col..] {
-                    cell.reset(&template);
-                }
-                if self.cursor.point.line < self.grid.num_lines() - 1 {
-                    self.grid
-                        .region_mut((self.cursor.point.line + 1)..)
-                        .each(|cell| cell.reset(&template));
-                }
-            },
-            ansi::ClearMode::All => self.grid.region_mut(..).each(|c| c.reset(&template)),
             ansi::ClearMode::Above => {
                 // If clearing more than one line
                 if self.cursor.point.line > Line(1) {
@@ -1774,6 +1765,23 @@ impl<T: EventListener> ansi::Handler for Term<T> {
                     cell.reset(&template);
                 }
             },
+            ansi::ClearMode::Below => {
+                for cell in &mut self.grid[self.cursor.point.line][self.cursor.point.col..] {
+                    cell.reset(&template);
+                }
+                if self.cursor.point.line < self.grid.num_lines() - 1 {
+                    self.grid
+                        .region_mut((self.cursor.point.line + 1)..)
+                        .each(|cell| cell.reset(&template));
+                }
+            },
+            ansi::ClearMode::All => {
+                if self.mode.contains(TermMode::ALT_SCREEN) {
+                    self.grid.region_mut(..).each(|c| c.reset(&template));
+                } else {
+                    self.grid.clear_viewport(&template);
+                }
+            },
             ansi::ClearMode::Saved => self.grid.clear_history(),
         }
     }