Add a mouse binding for empty areas of the window so C-Drag works on

them as well.

key-bindings.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: key-bindings.c,v 1.188 2026/07/13 16:30:28 nicm Exp $ */
+/* $OpenBSD: key-bindings.c,v 1.189 2026/07/15 10:38:31 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -503,6 +503,7 @@ 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 C-MouseDrag1Pane { new-pane -M }",
+		"bind -n C-MouseDrag1Empty { new-pane -M }",
 		"bind -n M-MouseDrag1Pane { move-pane -M }",
 
 		/* Mouse wheel up on pane. */

server-client.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: server-client.c,v 1.491 2026/07/14 19:07:03 nicm Exp $ */
+/* $OpenBSD: server-client.c,v 1.492 2026/07/15 10:38:31 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1033,46 +1033,46 @@ have_event:
 	 * Not on status line. Adjust position and check for border, pane, or
 	 * scrollbar.
 	 */
-	if (loc == KEYC_MOUSE_LOCATION_NOWHERE) {
+	if (loc == KEYC_MOUSE_LOCATION_NOWHERE && c->tty.mouse_scrolling_flag) {
-		if (c->tty.mouse_scrolling_flag) {
+		if (lwp != NULL) {
-			if (lwp != NULL) {
+			loc = KEYC_MOUSE_LOCATION_SCROLLBAR_SLIDER;
-				loc = KEYC_MOUSE_LOCATION_SCROLLBAR_SLIDER;
+			m->wp = lwp->id;
-				m->wp = lwp->id;
+			m->w = lwp->window->id;
-				m->w = lwp->window->id;
+		}
-			}
+	} else if (loc == KEYC_MOUSE_LOCATION_NOWHERE) {
+		px = x;
+		if (m->statusat == 0 && y >= m->statuslines)
+			py = y - m->statuslines;
+		else if (m->statusat > 0 && y >= (u_int)m->statusat)
+			py = m->statusat - 1;
+		else
+			py = y;
+
+		tty_window_offset(&c->tty, &m->ox, &m->oy, &sx, &sy);
+		log_debug("mouse window @%u at %u,%u (%ux%u)", w->id, m->ox,
+		    m->oy, sx, sy);
+		if (px > sx || py > sy) {
+			server_client_update_scrollbar_hover(c, type, -1, -1);
+			return (KEYC_UNKNOWN);
+		}
+		px = px + m->ox;
+		py = py + m->oy;
+		server_client_update_scrollbar_hover(c, type, px, py);
+
+		if (type == KEYC_TYPE_MOUSEDRAG && lwp != NULL) {
+			/* Use pane from last mouse event. */
+			wp = lwp;
+		} else {
+			/* Try inside the pane. */
+			wp = window_get_active_at(w, px, py);
+		}
+		if (wp == NULL) {
+			loc = KEYC_MOUSE_LOCATION_EMPTY;
+			m->w = w->id;
+			log_debug("mouse %u,%u on empty area", x, y);
 		} else {
-			px = x;
-			if (m->statusat == 0 && y >= m->statuslines)
-				py = y - m->statuslines;
-			else if (m->statusat > 0 && y >= (u_int)m->statusat)
-				py = m->statusat - 1;
-			else
-				py = y;
-
-			tty_window_offset(&c->tty, &m->ox, &m->oy, &sx, &sy);
-			log_debug("mouse window @%u at %u,%u (%ux%u)",
-				  w->id, m->ox, m->oy, sx, sy);
-			if (px > sx || py > sy) {
-				server_client_update_scrollbar_hover(c, type,
-				    -1, -1);
-				return (KEYC_UNKNOWN);
-			}
-			px = px + m->ox;
-			py = py + m->oy;
-			server_client_update_scrollbar_hover(c, type, px, py);
-
-			if (type == KEYC_TYPE_MOUSEDRAG && lwp != NULL) {
-				/* Use pane from last mouse event. */
-				wp = lwp;
-			} else {
-				/* Try inside the pane. */
-				wp = window_get_active_at(w, px, py);
-			}
-			if (wp == NULL)
-				return (KEYC_UNKNOWN);
 			loc = server_client_check_mouse_in_pane(wp, px, py,
 			    &sl_mpos);
-
 			if (loc == KEYC_MOUSE_LOCATION_PANE) {
 				log_debug("mouse %u,%u on pane %%%u", x, y,
 				    wp->id);

tmux.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1140 2026/07/14 17:17:18 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1141 2026/07/15 10:38:31 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: July 14 2026 $
+.Dd $Mdocdate: July 15 2026 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -6618,6 +6618,7 @@ and a location suffix, one of the following:
 .It Li "ScrollbarSlider" Ta "the scrollbar slider"
 .It Li "ScrollbarUp" Ta "above the scrollbar slider"
 .It Li "ScrollbarDown" Ta "below the scrollbar slider"
+.It Li "Empty" Ta "empty space in the window"
 .It Li "ControlN" Ta "on control range N"
 .El
 .Pp

tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1404 2026/07/14 19:07:03 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1405 2026/07/15 10:38:31 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -181,6 +181,7 @@ enum key_code_mouse_location {
 	KEYC_MOUSE_LOCATION_SCROLLBAR_UP,
 	KEYC_MOUSE_LOCATION_SCROLLBAR_SLIDER,
 	KEYC_MOUSE_LOCATION_SCROLLBAR_DOWN,
+	KEYC_MOUSE_LOCATION_EMPTY,
 	KEYC_MOUSE_LOCATION_CONTROL0, /* keep order */
 	KEYC_MOUSE_LOCATION_CONTROL1,
 	KEYC_MOUSE_LOCATION_CONTROL2,
@@ -237,6 +238,7 @@ enum key_code_mouse_location {
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, SCROLLBAR_UP),     \
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, SCROLLBAR_SLIDER), \
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, SCROLLBAR_DOWN),   \
+	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, EMPTY),            \
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, CONTROL0),         \
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, CONTROL1),         \
 	KEYC_MOUSE_KEY(KEYC_ ## t, KEYC_TYPE_ ## t, CONTROL2),         \
@@ -271,6 +273,7 @@ enum key_code_mouse_location {
 	{ #s "ScrollbarUp", KEYC_ ## name ## _SCROLLBAR_UP },         \
 	{ #s "ScrollbarSlider", KEYC_ ## name ## _SCROLLBAR_SLIDER }, \
 	{ #s "ScrollbarDown", KEYC_ ## name ## _SCROLLBAR_DOWN },     \
+	{ #s "Empty", KEYC_ ## name ## _EMPTY },		      \
 	{ #s "Border", KEYC_ ## name ## _BORDER },		      \
 	{ #s "Control0", KEYC_ ## name ## _CONTROL0 },		      \
 	{ #s "Control1", KEYC_ ## name ## _CONTROL1 },		      \