From 0da26b9320d17c7271436ba77828c90cb360081e Mon Sep 17 00:00:00 2001
From: Michael Grant <mgrant@grant.org>
Date: Tue, 16 Jun 2026 18:28:00 +0200
Subject: [PATCH] Implemented move-pane -M to allow one to bind alt-mouse1-drag
 to move a floating pane with the mouse.

---
 cmd-join-pane.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++--
 key-bindings.c  |  1 +
 2 files changed, 80 insertions(+), 2 deletions(-)

diff --git a/cmd-join-pane.c b/cmd-join-pane.c
index 04cc0676..9712eab5 100644
--- a/cmd-join-pane.c
+++ b/cmd-join-pane.c
@@ -30,6 +30,9 @@
  */
 
 static enum cmd_retval	cmd_join_pane_exec(struct cmd *, struct cmdq_item *);
+static enum cmd_retval	cmd_join_pane_mouse_update(struct cmdq_item *);
+static void		cmd_join_pane_mouse_update_move(struct client *,
+			    struct mouse_event *);
 
 const struct cmd_entry cmd_join_pane_entry = {
 	.name = "join-pane",
@@ -49,8 +52,8 @@ const struct cmd_entry cmd_move_pane_entry = {
 	.name = "move-pane",
 	.alias = "movep",
 
-	.args = { "bdfhvl:L::P:R::s:t:U::X:Y:z:", 0, 0, NULL },
-	.usage = "[-bdfhv] [-D lines] [-l size] [-L columns] [-P position] "
+	.args = { "bdfhMvl:L::P:R::s:t:U::X:Y:z:", 0, 0, NULL },
+	.usage = "[-bdfhMv] [-D lines] [-l size] [-L columns] [-P position] "
 	         "[-R columns] " CMD_SRCDST_PANE_USAGE " [-U lines] "
 	         "[-X x-position] [-Y y-position] [-z z-index]",
 
@@ -254,6 +257,78 @@ cmd_join_pane_move(struct cmdq_item *item, struct args *args,
 	return (CMD_RETURN_NORMAL);
 }
 
+static enum cmd_retval
+cmd_join_pane_mouse_update(struct cmdq_item *item)
+{
+	struct cmd_find_state	*target = cmdq_get_target(item);
+	struct key_event	*event = cmdq_get_event(item);
+	struct client		*c = cmdq_get_client(item);
+	struct session		*s = target->s;
+	struct winlink		*wl;
+	struct window		*w;
+	struct window_pane	*wp;
+
+	if (!event->m.valid)
+		return (CMD_RETURN_NORMAL);
+	wp = cmd_mouse_pane(&event->m, &s, &wl);
+	if (wp == NULL || c == NULL || c->session != s)
+		return (CMD_RETURN_NORMAL);
+	if (!window_pane_is_floating(wp))
+		return (CMD_RETURN_NORMAL);
+
+	w = wl->window;
+	window_redraw_active_switch(w, wp);
+	window_set_active_pane(w, wp, 1);
+
+	/* Set up mouse_drag_update callback. */
+	c->tty.mouse_drag_update =
+	     cmd_join_pane_mouse_update_move;
+	 cmd_join_pane_mouse_update_move(c, &event->m);
+	return (CMD_RETURN_NORMAL);
+}
+
+/*
+ * Moves the pane by dragging.
+ * server-client.c calls c->tty.mouse_drag_update(c, m) which
+ * calls this function.
+ */
+static void cmd_join_pane_mouse_update_move(struct client *c,
+    struct mouse_event *m)
+{
+	struct winlink		*wl;
+	struct window		*w;
+	struct window_pane	*wp;
+	struct layout_cell	*lc;
+	int			 y, ly, x, lx;
+
+	wp = cmd_mouse_pane(m, NULL, &wl);
+	if (wp == NULL) {
+		c->tty.mouse_drag_update = NULL;
+		return;
+	}
+	w = wl->window;
+	lc = wp->layout_cell;
+
+	y = m->y + m->oy; x = m->x + m->ox;
+	if (m->statusat == 0 && y >= (int)m->statuslines)
+		y -= m->statuslines;
+	else if (m->statusat > 0 && y >= m->statusat)
+		y = m->statusat - 1;
+	ly = m->ly + m->oy; lx = m->lx + m->ox;
+	if (m->statusat == 0 && ly >= (int)m->statuslines)
+		ly -= m->statuslines;
+	else if (m->statusat > 0 && ly >= m->statusat)
+		ly = m->statusat - 1;
+
+	if (x != lx || y != ly) {
+		lc->xoff += x - lx;
+		lc->yoff += y - ly;
+		layout_fix_panes(w, NULL);
+		server_redraw_window(w);
+		server_redraw_window_borders(w);
+	}
+}
+
 static enum cmd_retval
 cmd_join_pane_zindex(struct cmdq_item *item, struct winlink *wl,
     struct window_pane *wp, const char *s)
@@ -314,6 +389,8 @@ cmd_join_pane_exec(struct cmd *self, struct cmdq_item *item)
 	server_unzoom_window(dst_w);
 
 	if (cmd_get_entry(self) == &cmd_move_pane_entry) {
+		if (args_has(args, 'M'))
+			return (cmd_join_pane_mouse_update(item));
 		if (!window_pane_is_floating(dst_wp)) {
 			cmdq_error(item, "pane is not floating");
 			return (CMD_RETURN_ERROR);
diff --git a/key-bindings.c b/key-bindings.c
index 08d4c5f6..afdd5728 100644
--- a/key-bindings.c
+++ b/key-bindings.c
@@ -468,6 +468,7 @@ key_bindings_init(void)
 
 		/* Mouse button 1 drag on border. */
 		"bind -n MouseDrag1Border { resize-pane -M }",
+		"bind -n M-MouseDrag1Border { move-pane -M }",
 
 		/* Mouse button 1 down on status line. */
 		"bind -n MouseDown1Status { switch-client -t= }",