Scroll a tag taller than its rows to keep its caret in view

A tag shows at most eight rows, so a longer one (a 9P write of many lines, or
`o` in the tag) put its caret on a line that was never drawn. Pane, column and
workspace tags now keep a first line on screen that follows the caret while
they have the keyboard, and the pointer and the pane text count their rows
from it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/tagline.zig b/src/tagline.zig
index 1021e9db..a918689b 100644
--- a/src/tagline.zig
+++ b/src/tagline.zig
@@ -81,10 +81,15 @@ pub fn focusedHeader(p: *Pardes) ?*Text {
 pub fn revealHeader(p: *Pardes) void {
     const t = focusedHeader(p) orelse {
         p.header_scroll = 0;
+        p.header_top = 0;
         return;
     };
     const text = edit.flatSurface(p, t) catch return;
-    const line = modal.lineSlice(text, @intCast(@max(0, t.cur_row)));
+    const cur: usize = @intCast(@max(0, t.cur_row));
+    const rows: usize = if (p.header_column != null) p.columnBarHeight() else p.topBarHeight();
+    if (cur < p.header_top) p.header_top = cur;
+    if (rows > 0 and cur >= p.header_top + rows) p.header_top = cur + 1 - rows;
+    const line = modal.lineSlice(text, cur);
     const width = p.tagCapacity(if (p.header_column) |c| p.col_w[c] -| TAG_TEXT_INSET else p.screen_w);
     const col = panes.File.rawDisplayCol(line, @min(@as(usize, @intCast(@max(0, t.cur_col))), line.len));
     if (col < p.header_scroll) p.header_scroll = col;
@@ -187,10 +192,11 @@ pub fn enterTag(p: *Pardes, pane: *Pane) void {
 /// lands in the tag's own text, or null when it is on the prefix, which
 /// only the first line has.
 pub fn tagOffsetAt(p: *Pardes, pane: *Pane, row: usize, col: usize) ?modal.Cursor {
-    const width = if (row == 0) panes.File.displayWidth(tagPrefix(p, pane) catch return null) else 0;
+    const at = row + pane.tag_top;
+    const width = if (at == 0) panes.File.displayWidth(tagPrefix(p, pane) catch return null) else 0;
     if (col < width) return null;
-    const line = modal.lineSlice(curTail(pane), row);
-    return .{ .row = row, .col = modal.graphemeStart(line, panes.File.rawAtDisplay(line, col - width)) };
+    const line = modal.lineSlice(curTail(pane), at);
+    return .{ .row = at, .col = modal.graphemeStart(line, panes.File.rawAtDisplay(line, col - width)) };
 }
 
 /// Start a name draft for a file that can take one, its caret at display
@@ -235,6 +241,7 @@ pub fn exitHeader(p: *Pardes) void {
     p.header_column = null;
     p.header_drag = false;
     p.header_scroll = 0;
+    p.header_top = 0;
 }
 
 /// Give the keyboard to a column's tag, or the workspace's for null, in