From 6b1d99dc6e3ef47c63221a332a66cb062cf11782 Mon Sep 17 00:00:00 2001
From: Tim Culverhouse <tim@timculverhouse.com>
Date: Tue, 26 Sep 2023 22:06:29 -0500
Subject: [PATCH] terminal: rows created from IND should inherit the current bg
 attr

Any row created from scrolling via IND ("\x1BD") should have it's
background set as the current background. This can be verified in any
terminal with

  $ echo -e "\x1B[41m" && cat -v"

Followed by pressing enter to scroll the screen. We expect to see red
rows appear. Add test case to verify.

Fixes: alacritty/vim_large_screen_scroll
---
 src/terminal/Screen.zig | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/terminal/Screen.zig b/src/terminal/Screen.zig
index 34355d6b9..195f5962f 100644
--- a/src/terminal/Screen.zig
+++ b/src/terminal/Screen.zig
@@ -1753,10 +1753,31 @@ fn scrollDelta(self: *Screen, delta: isize, viewport_only: bool) !void {
     }
 
     // Ensure we have "written" our last row so that it shows up
-    _ = self.storage.getPtrSlice(
+    const slices = self.storage.getPtrSlice(
         (rows_written_final - 1) * (self.cols + 1),
         self.cols + 1,
     );
+    // We should never be wrapped here
+    assert(slices[1].len == 0);
+
+    // We only grabbed our new row(s), copy cells into the whole slice
+    const dst = slices[0];
+    // The pen we'll use for new cells (only the BG attribute is applied to new
+    // cells)
+    const pen: Cell = if (!self.cursor.pen.attrs.has_bg) .{} else .{
+        .bg = self.cursor.pen.bg,
+        .attrs = .{ .has_bg = true },
+    };
+    @memset(dst, .{ .cell = pen });
+
+    // Then we make sure our row headers are zeroed out. We set
+    // the value to a dirty row header so that the renderer re-draws.
+    var i: usize = 0;
+    while (i < dst.len) : (i += self.cols + 1) {
+        dst[i] = .{ .header = .{
+            .flags = .{ .dirty = true },
+        } };
+    }
 
     if (start_viewport_bottom) {
         // If our viewport is on the bottom, we always update the viewport
@@ -3126,6 +3147,8 @@ test "Screen: scrolling" {
 
     var s = try init(alloc, 3, 5, 0);
     defer s.deinit();
+    s.cursor.pen.bg = .{ .r = 155 };
+    s.cursor.pen.attrs.has_bg = true;
     try s.testWriteString("1ABCD\n2EFGH\n3IJKL");
     try testing.expect(s.viewportIsBottom());
 
@@ -3139,6 +3162,11 @@ test "Screen: scrolling" {
         defer alloc.free(contents);
         try testing.expectEqualStrings("2EFGH\n3IJKL", contents);
     }
+    {
+        // Test that our new row has the correct background
+        const cell = s.getCell(.active, 2, 0);
+        try testing.expectEqual(@as(u8, 155), cell.bg.r);
+    }
 
     // Scrolling to the bottom does nothing
     try s.scroll(.{ .bottom = {} });