fix(compatibility): ansi scroll down (#1279)

* fix(compatibility): ansi scroll down

* style(fmt): rustfmt

4 files changed, 94 insertions, 16 deletions

diff --git a/src/tests/fixtures/scroll_down b/src/tests/fixtures/scroll_down
new file mode 100755
index 000000000..5a194bbe8
--- /dev/null
+++ b/src/tests/fixtures/scroll_down
@@ -0,0 +1,3 @@
+
+
+line1line2
diff --git a/zellij-server/src/panes/grid.rs b/zellij-server/src/panes/grid.rs
index fe1a81ea0..fd06967ae 100644
--- a/zellij-server/src/panes/grid.rs
+++ b/zellij-server/src/panes/grid.rs
@@ -814,30 +814,31 @@ impl Grid {
         }
     }
     pub fn rotate_scroll_region_up(&mut self, count: usize) {
-        if let Some((scroll_region_top, scroll_region_bottom)) = self.scroll_region {
+        if let Some((scroll_region_top, scroll_region_bottom)) = self
+            .scroll_region
+            .or(Some((0, self.height.saturating_sub(1))))
+        {
             for _ in 0..count {
-                let columns = VecDeque::from(vec![EMPTY_TERMINAL_CHARACTER; self.width]);
-                if scroll_region_bottom < self.viewport.len() {
-                    self.viewport.remove(scroll_region_bottom);
-                }
-                if scroll_region_top < self.viewport.len() {
-                    self.viewport
-                        .insert(scroll_region_top, Row::from_columns(columns).canonical());
+                if self.cursor.y >= scroll_region_top && self.cursor.y <= scroll_region_bottom {
+                    self.pad_lines_until(scroll_region_bottom, EMPTY_TERMINAL_CHARACTER);
+                    if self.viewport.get(scroll_region_bottom).is_some() {
+                        self.viewport.remove(scroll_region_bottom);
+                    }
                 }
             }
             self.output_buffer.update_all_lines(); // TODO: only update scroll region lines
         }
     }
     pub fn rotate_scroll_region_down(&mut self, count: usize) {
-        if let Some((scroll_region_top, scroll_region_bottom)) = self.scroll_region {
+        if let Some((scroll_region_top, scroll_region_bottom)) = self
+            .scroll_region
+            .or(Some((0, self.height.saturating_sub(1))))
+        {
             for _ in 0..count {
-                let columns = VecDeque::from(vec![EMPTY_TERMINAL_CHARACTER; self.width]);
-                self.viewport.remove(scroll_region_top);
-                if self.viewport.len() > scroll_region_top {
-                    self.viewport
-                        .insert(scroll_region_bottom, Row::from_columns(columns).canonical());
-                } else {
-                    self.viewport.push(Row::from_columns(columns).canonical());
+                if self.cursor.y >= scroll_region_top && self.cursor.y <= scroll_region_bottom {
+                    self.pad_lines_until(scroll_region_top, EMPTY_TERMINAL_CHARACTER);
+                    self.viewport.remove(scroll_region_top);
+                    self.pad_lines_until(scroll_region_bottom, EMPTY_TERMINAL_CHARACTER);
                 }
             }
             self.output_buffer.update_all_lines(); // TODO: only update scroll region lines
diff --git a/zellij-server/src/panes/unit/grid_tests.rs b/zellij-server/src/panes/unit/grid_tests.rs
index e4b15503c..a03849a40 100644
--- a/zellij-server/src/panes/unit/grid_tests.rs
+++ b/zellij-server/src/panes/unit/grid_tests.rs
@@ -1602,3 +1602,20 @@ pub fn replace_non_wide_characters_with_wide_characters() {
     }
     assert_snapshot!(format!("{:?}", grid));
 }
+
+#[test]
+pub fn scroll_down_ansi() {
+    let mut vte_parser = vte::Parser::new();
+    let mut grid = Grid::new(
+        51,
+        112,
+        Palette::default(),
+        Rc::new(RefCell::new(LinkHandler::new())),
+    );
+    let fixture_name = "scroll_down";
+    let content = read_fixture(fixture_name);
+    for byte in content {
+        vte_parser.advance(&mut grid, byte);
+    }
+    assert_snapshot!(format!("{:?}", grid));
+}
diff --git a/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__scroll_down_ansi.snap b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__scroll_down_ansi.snap
new file mode 100644
index 000000000..7a9418a37
--- /dev/null
+++ b/zellij-server/src/panes/unit/snapshots/zellij_server__panes__grid__grid_tests__scroll_down_ansi.snap
@@ -0,0 +1,57 @@
+---
+source: zellij-server/src/panes/./unit/grid_tests.rs
+assertion_line: 1620
+expression: "format!(\"{:?}\", grid)"
+---
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