1 files changed, 17 insertions, 0 deletions
diff --git a/src/layout.zig b/src/layout.zig
index c6cb7503..8db05a07 100644
--- a/src/layout.zig
+++ b/src/layout.zig
@@ -723,6 +723,23 @@ pub fn columnMoveTarget(p: *const Pardes, source: usize, x: u16) usize {
     return insertion;
 }
 
+/// Share out the width of columns `left` and `left + 1` so the left one is
+/// `left_width` cells, neither below MINW. A border drag and a column grip
+/// dropped inside its own place both end here.
+pub fn setColumnPairWidth(p: *Pardes, left: usize, left_width: u64) void {
+    if (left + 1 >= p.ncol) return;
+    const combined: u64 = p.col_w[left] + p.col_w[left + 1];
+    // Too narrow for both to keep MINW: any split would squeeze one away.
+    if (combined < 2 * @as(u64, config.MINW)) return;
+    const width = std.math.clamp(left_width, config.MINW, @max(@as(u64, config.MINW), combined -| config.MINW));
+    const pair = p.col_weight[left] + p.col_weight[left + 1];
+    if (pair <= 1 or combined == 0) return;
+    const numerator = @as(u128, pair) * width + combined / 2;
+    const share = std.math.clamp(@as(u64, @intCast(numerator / combined)), 1, pair - 1);
+    p.col_weight[left] = share;
+    p.col_weight[left + 1] = pair - share;
+}
+
 pub fn reorderColumn(p: *Pardes, from: usize, to: usize) void {
     if (from >= p.ncol or to >= p.ncol or from == to) return;
     const ids = p.col_panes[from];