Fix colored row reset performance

This fixes a bug where a row would always get reset completely if its
background does not equal the default terminal background. This leads to
big performance bottlenecks when running commands like `echo "\e[41m" &&
yes`.

Instead of resetting the entire row whenever the template cell is not
empty, the template cell is now compared to the last cell in the row.
The last cell will always be equal to the previous template cell when
`row.occ < row.inner.len()` and if `occ` is equal to the row's length,
the entire row is always reset anyways.

Fixes #2989.

1 files changed, 7 insertions, 1 deletions

diff --git a/alacritty_terminal/src/grid/mod.rs b/alacritty_terminal/src/grid/mod.rs
index 09333b36..ad9d9b7b 100644
--- a/alacritty_terminal/src/grid/mod.rs
+++ b/alacritty_terminal/src/grid/mod.rs
@@ -70,6 +70,12 @@ pub trait GridCell {
     fn is_empty(&self) -> bool;
     fn is_wrap(&self) -> bool;
     fn set_wrap(&mut self, wrap: bool);
+
+    /// Fast equality approximation.
+    ///
+    /// This is a faster alternative to [`PartialEq`],
+    /// but might report inequal cells as equal.
+    fn fast_eq(&self, other: Self) -> bool;
 }
 
 /// Represents the terminal display contents
@@ -140,7 +146,7 @@ pub enum Scroll {
     Bottom,
 }
 
-impl<T: GridCell + Copy + Clone> Grid<T> {
+impl<T: GridCell + PartialEq + Copy> Grid<T> {
     pub fn new(lines: index::Line, cols: index::Column, scrollback: usize, template: T) -> Grid<T> {
         let raw = Storage::with_capacity(lines, Row::new(cols, &template));
         Grid {