Skip displaying unchanged cells

src/main.rs

@@ -65,17 +65,19 @@ impl GlyphCache {
         }
     }
 
-    pub fn lookup(&mut self, cell: &Cell) -> &[u32] {
-        let glyph_info = GlyphInfo {
+    pub fn cell_info(&self, cell: &Cell) -> GlyphInfo {
+        GlyphInfo {
             c: cell.c,
             fg: self.color_to_u32(&cell.fg),
             bg: self.color_to_u32(&cell.bg),
             flags: cell.flags,
-        };
+        }
+    }
 
+    pub fn lookup(&mut self, glyph: &GlyphInfo) -> &[u32] {
         self.glyphs
-            .entry(glyph_info.clone())
-            .or_insert_with(|| self.renderer.draw(&glyph_info).into_boxed_slice())
+            .entry(glyph.clone())
+            .or_insert_with(|| self.renderer.draw(glyph).into_boxed_slice())
     }
 
     // TODO deduplicate
@@ -164,6 +166,7 @@ impl BitmapGlyphRenderer {
 
 pub struct Graphics {
     glyph_cache: GlyphCache,
+    cell_cache: HashMap<(usize, usize), GlyphInfo>,
     width: usize,
     height: usize,
     cell_width: usize,
@@ -182,6 +185,7 @@ impl Graphics {
         Self::load_colors(&mut colors);
 
         let glyph_cache = GlyphCache::new(colors.clone());
+        let cell_cache = Default::default();
 
         Self {
             width,
@@ -189,6 +193,7 @@ impl Graphics {
             cell_width: glyph_cache.renderer.cell_width,
             cell_height: glyph_cache.renderer.cell_height,
             glyph_cache,
+            cell_cache,
             colors,
             buffer,
         }
@@ -259,6 +264,8 @@ impl Graphics {
 
         self.buffer.clear();
         self.buffer.resize(width * height, 0);
+
+        self.cell_cache.clear();
     }
 
     pub fn redraw(&mut self, term: &Term<TermListener>, context: &mut GraphicsContext<Window>) {
@@ -267,12 +274,19 @@ impl Graphics {
             (size.width as usize, size.height as usize)
         };
 
-        let mut buffer = vec![0u32; (width * height) as usize];
+        if width != self.width || height != self.height {
+            self.resize(width, height);
+        }
+
+        let cursor_color = Color::Named(NamedColor::Foreground);
+        let cursor_color = self.color_to_u32(&cursor_color);
+        let buffer = self.buffer.as_mut_slice();
         let content = term.renderable_content();
 
         for cell in content.display_iter.into_iter() {
             let term_row = cell.point.line.0 as usize;
             let term_col = cell.point.column.0 as usize;
+            let term_coords = (term_row, term_col);
 
             if (term_row + 1) * self.cell_height >= height
                 || (term_col + 1) * self.cell_width >= width
@@ -284,7 +298,15 @@ impl Graphics {
                 continue;
             }
 
-            let glyph = self.glyph_cache.lookup(&cell);
+            let glyph_info = self.glyph_cache.cell_info(&cell);
+
+            if self.cell_cache.get(&term_coords) == Some(&glyph_info) {
+                continue;
+            } else {
+                self.cell_cache.insert(term_coords, glyph_info.clone());
+            }
+
+            let glyph = self.glyph_cache.lookup(&glyph_info);
             let px_row = term_row * self.cell_height * width;
             let mut px_start = px_row + term_col * self.cell_width;
 
@@ -303,12 +325,12 @@ impl Graphics {
 
         let term_row = content.cursor.point.line.0 as usize;
         let term_col = content.cursor.point.column.0 as usize;
+        let term_coords = (term_row, term_col);
 
         if (term_row + 1) * self.cell_height < height && (term_col + 1) * self.cell_width < width {
-            let mut px_row = term_row * width * self.cell_height + term_col * self.cell_width;
+            self.cell_cache.remove(&term_coords);
 
-            let cursor_color = Color::Named(NamedColor::Foreground);
-            let cursor_color = self.color_to_u32(&cursor_color);
+            let mut px_row = term_row * width * self.cell_height + term_col * self.cell_width;
 
             use alacritty_terminal::ansi::CursorShape;
             match content.cursor.shape {