Add -M to move-pane and default bindings for M-drag. From Michael Grant.

cmd-join-pane.c

@@ -31,6 +31,9 @@
  */
 
 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_move(struct client *,
+			    struct mouse_event *);
 
 const struct cmd_entry cmd_join_pane_entry = {
 	.name = "join-pane",
@@ -50,8 +53,8 @@ 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 },
+	.args = { "bdfhMvl:L::P:R::s:t:U::X:Y:z:", 0, 0, NULL },
-	.usage = "[-bdfhv] [-D lines] [-l size] [-L columns] [-P position] "
+	.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]",
 
@@ -255,6 +258,71 @@ 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);
+
+	c->tty.mouse_drag_update = cmd_join_pane_mouse_move;
+	cmd_join_pane_mouse_move(c, &event->m);
+	return (CMD_RETURN_NORMAL);
+}
+
+static void
+cmd_join_pane_mouse_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)
@@ -315,6 +383,8 @@ 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);

cmd-resize-pane.c

@@ -31,9 +31,9 @@ static enum cmd_retval	cmd_resize_pane_exec(struct cmd *, struct cmdq_item *);
 
 static enum cmd_retval	cmd_resize_pane_mouse_update(struct cmd *,
 			    struct cmdq_item *);
-static void		cmd_resize_pane_mouse_update_floating(struct client *,
+static void		cmd_resize_pane_mouse_resize_move_floating(
-			    struct mouse_event *);
+			    struct client *, struct mouse_event *);
-static void		cmd_resize_pane_mouse_update_tiled(struct client *,
+static void		cmd_resize_pane_mouse_resize_tiled(struct client *,
 			    struct mouse_event *);
 
 const struct cmd_entry cmd_resize_pane_entry = {
@@ -205,21 +205,29 @@ cmd_resize_pane_mouse_update(__unused struct cmd *self, struct cmdq_item *item)
 		return (CMD_RETURN_NORMAL);
 
 	if (!window_pane_is_floating(wp)) {
-		c->tty.mouse_drag_update = cmd_resize_pane_mouse_update_tiled;
+		c->tty.mouse_drag_update = cmd_resize_pane_mouse_resize_tiled;
-		cmd_resize_pane_mouse_update_tiled(c, &event->m);
+		cmd_resize_pane_mouse_resize_tiled(c, &event->m);
 		return (CMD_RETURN_NORMAL);
 	}
 
 	window_redraw_active_switch(w, wp);
 	window_set_active_pane(w, wp, 1);
 
-	c->tty.mouse_drag_update = cmd_resize_pane_mouse_update_floating;
+	c->tty.mouse_drag_update = cmd_resize_pane_mouse_resize_move_floating;
-	cmd_resize_pane_mouse_update_floating(c, &event->m);
+	cmd_resize_pane_mouse_resize_move_floating(c, &event->m);
 	return (CMD_RETURN_NORMAL);
 }
 
+/*
+ * Resizes or moves the pane by dragging. Resize a floating pane by dragging
+ * the borders or corners. Grabbing an edge only resizes that axis (special
+ * case). Moves the pane if dragging the top border. Since characters are
+ * generally rectangular, to make it easier to grab the corner, the character
+ * next to the corner is also considered the corner.
+ */
 static void
-cmd_resize_pane_mouse_update_floating(struct client *c, struct mouse_event *m)
+cmd_resize_pane_mouse_resize_move_floating(struct client *c,
+    struct mouse_event *m)
 {
 	struct winlink		*wl;
 	struct window		*w;
@@ -345,7 +353,7 @@ cmd_resize_pane_mouse_update_floating(struct client *c, struct mouse_event *m)
 }
 
 static void
-cmd_resize_pane_mouse_update_tiled(struct client *c, struct mouse_event *m)
+cmd_resize_pane_mouse_resize_tiled(struct client *c, struct mouse_event *m)
 {
 	struct winlink		*wl;
 	struct window		*w;

key-bindings.c

@@ -450,6 +450,7 @@ key_bindings_init(void)
 
 		/* Mouse button 1 drag on pane. */
 		"bind -n MouseDrag1Pane { if -F '#{||:#{pane_in_mode},#{mouse_any_flag}}' { send -M } { copy-mode -M } }",
+		"bind -n M-MouseDrag1Pane { move-pane -M }",
 
 		/* Mouse wheel up on pane. */
 		"bind -n WheelUpPane { if -F '#{||:#{alternate_on},#{pane_in_mode},#{mouse_any_flag}}' { send -M } { copy-mode -e } }",
@@ -468,6 +469,7 @@ 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= }",

tmux.1

@@ -3313,7 +3313,7 @@ or
 reverses the sort order.
 .Tg movep
 .It Xo Ic move\-pane
-.Op Fl bdfhv
+.Op Fl bdfhMv
 .Op Fl D Op Ar lines
 .Op Fl l Ar size
 .Op Fl L Op Ar columns
@@ -3385,6 +3385,10 @@ move it to an absolute position.
 moves the pane to the given
 .Ar z-index ,
 where zero is the front.
+.Pp
+.Fl M
+begins a mouse drag (only valid if bound to a mouse key binding, see
+.Sx MOUSE SUPPORT ) .
 .Tg movew
 .It Xo Ic move\-window
 .Op Fl abrdk