1 files changed, 60 insertions, 9 deletions

diff --git a/src/layout.zig b/src/layout.zig
index 644054ed..cbf0fd96 100644
--- a/src/layout.zig
+++ b/src/layout.zig
@@ -274,7 +274,11 @@ pub fn applyRowSplit(p: *Pardes, cc: usize, k: usize, cur_y: u16) void {
     const rb = p.rects[p.col_panes[cc][k + 1]];
     const combined: f32 = @floatFromInt(ra.h + rb.h);
     var nt: f32 = @floatFromInt(if (p.settings.tag_bottom) cur_y -| ra.y else (cur_y + 1) -| ra.y);
-    nt = std.math.clamp(nt, @as(f32, BOX_H), @max(@as(f32, BOX_H), combined - BOX_H));
+    // A terminal keeps its tag and two body rows (floorRows); a text pane
+    // gives up all but its tag, as acme's do.
+    const lo: f32 = @floatFromInt(@max(BOX_H, floorRows(p, p.col_panes[cc][k])));
+    const hi = combined - @as(f32, @floatFromInt(@max(BOX_H, floorRows(p, p.col_panes[cc][k + 1]))));
+    nt = std.math.clamp(nt, @min(lo, @max(@as(f32, BOX_H), hi)), @max(@as(f32, BOX_H), hi));
     if (combined <= 0) return;
     // Dragging a folded tag open is an explicit resize, so switch this pair
     // back to visible-height weights without consuming other folded weights.
@@ -794,16 +798,62 @@ pub fn compute(p: *Pardes) void {
         if (vsum <= 0) vsum = 1;
 
         var y: u16 = p.topBarHeight() + p.columnBarHeight();
+        const top = y;
         const avail_h = p.screen_h -| y;
-        for (0..p.col_n[c]) |k| {
+        var hs: [MAX_PANES]u16 = undefined;
+        const n = p.col_n[c];
+        for (0..n) |k| {
             const id = p.col_panes[c][k];
-            const pane = p.panes[id] orelse continue;
-            const lastk = k + 1 == p.col_n[c];
+            const pane = p.panes[id] orelse {
+                hs[k] = 0;
+                continue;
+            };
+            const lastk = k + 1 == n;
             const fh = @as(f32, @floatFromInt(avail_h)) * pane.vweight / vsum;
             const room = p.screen_h -| y;
-            const ch: u16 = if (lastk) room else @min(room, @max(1, @as(u16, @intFromFloat(@round(fh)))));
-            p.rects[id] = .{ .x = x, .y = y, .w = cw, .h = ch };
-            y +|= ch;
+            hs[k] = if (lastk) room else @min(room, @max(1, @as(u16, @intFromFloat(@round(fh)))));
+            y +|= hs[k];
+        }
+        keepTerminalFloors(p, c, hs[0..n]);
+        y = top;
+        for (0..n) |k| {
+            const id = p.col_panes[c][k];
+            if (p.panes[id] == null) continue;
+            p.rects[id] = .{ .x = x, .y = y, .w = cw, .h = hs[k] };
+            y +|= hs[k];
+        }
+    }
+}
+
+/// The fewest rows a pane is laid out with: a terminal keeps its tag and
+/// `min_body_rows` (a shorter one loses its prompt and reads busy for
+/// ever), a text pane may shrink to its tag, as acme's windows do.
+fn floorRows(p: *Pardes, id: usize) u16 {
+    const pane = p.panes[id] orelse return 0;
+    return if (pane.isTerminal()) @max(1, pane.tag_rows) + min_body_rows else 1;
+}
+
+/// Raises each terminal in column `c` below its floor to it, a row at a
+/// time from whichever pane has the most rows above its own floor. Where
+/// the column has not the rows, the terminal keeps what it could get.
+// ponytail: a row per step, O(panes x rows); a column holds few of both.
+fn keepTerminalFloors(p: *Pardes, c: usize, hs: []u16) void {
+    for (hs, 0..) |*h, k| {
+        const floor = floorRows(p, p.col_panes[c][k]);
+        while (h.* < floor) {
+            var giver: ?usize = null;
+            var spare: u16 = 0;
+            for (hs, 0..) |other, j| {
+                if (j == k) continue;
+                const extra = other -| floorRows(p, p.col_panes[c][j]);
+                if (extra > spare) {
+                    spare = extra;
+                    giver = j;
+                }
+            }
+            const g = giver orelse break;
+            hs[g] -= 1;
+            h.* += 1;
         }
     }
 }
@@ -911,9 +961,10 @@ test "collapse local transfers remain bounded through repeated tiny window resiz
 test "collapse expansion is limited to space available in one neighbor" {
     const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 42 });
     defer p.deinit();
+    // Text panes: a terminal would keep its tag and two rows (floorRows).
     for (1..4) |id| {
-        _ = try p.newShell(id, "");
-        insert(p, 0, id, id);
+        p.newScratchBelow(0);
+        try std.testing.expectEqual(id, p.col_panes[0][id]);
     }
     compute(p);
     toggleCollapse(p, 2);