xdg-shell: Turn the resizing heuristics into an explicit state

Currently, there's a race condition. When resizing from the left, and
a client attaches a buffer after the resize ends, you suddenly see the
buffer jump to the right, because the resize ended while multiple
attaches were in-flight. Making resize a state can fix this, as the
server can now know exactly when the resize ended, and whether a commit
was before or after that place.

We don't implement the correct tracking in this commit; that's left as
an exercise to the reader.

Additionally, clients like terminals might want to display resize popups
to display the number of cells when in a resize. They can use the hint
here to figure out whether they are resizing.

clients/window.c

@@ -2387,7 +2387,6 @@ frame_handle_status(struct window_frame *frame, struct input *input,
 	if ((status & FRAME_STATUS_RESIZE) && window->xdg_surface) {
 		input_ungrab(input);
 
-		window->resizing = 1;
 		xdg_surface_resize(window->xdg_surface,
 				   input_get_seat(input),
 				   window->display->serial,
@@ -2623,12 +2622,6 @@ pointer_handle_enter(void *data, struct wl_pointer *pointer,
 	input->pointer_enter_serial = serial;
 	input->pointer_focus = window;
 
-	if (window->resizing) {
-		window->resizing = 0;
-		/* Schedule a redraw to free the pool */
-		window_schedule_redraw(window);
-	}
-
 	input->sx = sx;
 	input->sy = sy;
 
@@ -3873,6 +3866,7 @@ handle_surface_configure(void *data, struct xdg_surface *xdg_surface,
 
 	window->maximized = 0;
 	window->fullscreen = 0;
+	window->resizing = 0;
 
 	wl_array_for_each(p, states) {
 		uint32_t state = *p;
@@ -3883,6 +3877,9 @@ handle_surface_configure(void *data, struct xdg_surface *xdg_surface,
 		case XDG_SURFACE_STATE_FULLSCREEN:
 			window->fullscreen = 1;
 			break;
+		case XDG_SURFACE_STATE_RESIZING:
+			window->resizing = 1;
+			break;
 		default:
 			/* Unknown state */
 			break;

desktop-shell/shell.c

@@ -351,13 +351,27 @@ shell_grab_start(struct shell_grab *grab,
 	}
 }
 
+static void
+shell_surface_state_changed(struct shell_surface *shsurf)
+{
+	if (shell_surface_is_xdg_surface(shsurf)) {
+		shsurf->client->send_configure(shsurf->surface,
+					       shsurf->surface->width,
+					       shsurf->surface->height);
+	}
+}
+
 static void
 shell_grab_end(struct shell_grab *grab)
 {
 	if (grab->shsurf) {
 		wl_list_remove(&grab->shsurf_destroy_listener.link);
 		grab->shsurf->grabbed = 0;
-		grab->shsurf->resize_edges = 0;
+
+		if (grab->shsurf->resize_edges) {
+			grab->shsurf->resize_edges = 0;
+			shell_surface_state_changed(grab->shsurf);
+		}
 	}
 
 	weston_pointer_end_grab(grab->grab.pointer);
@@ -1769,6 +1783,7 @@ surface_resize(struct shell_surface *shsurf,
 	                                &resize->width, &resize->height);
 
 	shsurf->resize_edges = edges;
+	shell_surface_state_changed(shsurf);
 	shell_grab_start(&resize->base, &resize_grab_interface, shsurf,
 			 seat->pointer, edges);
 
@@ -3538,6 +3553,10 @@ xdg_send_configure(struct weston_surface *surface,
 		s = wl_array_add(&states, sizeof *s);
 		*s = XDG_SURFACE_STATE_MAXIMIZED;
 	}
+	if (shsurf->resize_edges != 0) {
+		s = wl_array_add(&states, sizeof *s);
+		*s = XDG_SURFACE_STATE_RESIZING;
+	}
 
 	serial = wl_display_next_serial(shsurf->surface->compositor->wl_display);
 	xdg_surface_send_configure(shsurf->resource, width, height, &states, serial);

protocol/xdg-shell.xml

@@ -270,6 +270,12 @@
         The surface is fullscreen. The window geometry specified in the configure
         event must be obeyed by the client.
       </entry>
+      <entry name="resizing" value="3">
+        The surface is being resized. The window geometry specified in the
+        configure event is a maximum; the client cannot resize beyond it.
+        Clients that have aspect ratio or cell sizing configuration can use
+        a smaller size, however.
+      </entry>
     </enum>
 
     <event name="configure">