xwm: use _XWAYLAND_ALLOW_COMMITS

This patch uses the new feature proposed for Xwayland in the patch
series https://patchwork.freedesktop.org/series/16610/ .

When the frame window is created, immediately forbid Xwayland commits on
it. This prevents commits before the decorations have been drawn and the
initial pending state has been set. Commits are enabled right after
drawing and setting.

This ensures that the decorations are fully drawn when a window is
mapped. This also solves the initial commit/pending race, but the race
is on again after mapping.

If Xwayland does not implement the needed support, we are just setting a
window property with no effect.

This patch is the final piece for solving T7622, excluding the
_NET_WM_SYNC_REQUEST handling.

Task: https://phabricator.freedesktop.org/T7622
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Acked-by: Daniel Stone <daniels@collabora.com>

xwayland/window-manager.c

@@ -873,6 +873,37 @@ weston_wm_window_activate(struct wl_listener *listener, void *data)
 
 }
 
+/** Control Xwayland wl_surface.commit behaviour
+ *
+ * This function sets the "_XWAYLAND_ALLOW_COMMITS" property of the frame window
+ * (not the content window!) to \p allow.
+ *
+ * If the property is set to \c true, Xwayland will commit whenever it likes.
+ * If the property is set to \c false, Xwayland will not commit.
+ * If the property is not set at all, Xwayland assumes it is \c true.
+ *
+ * \param window The XWM window to control.
+ * \param allow Whether Xwayland is allowed to wl_surface.commit for the window.
+ */
+static void
+weston_wm_window_set_allow_commits(struct weston_wm_window *window, bool allow)
+{
+	struct weston_wm *wm = window->wm;
+	uint32_t property[1];
+
+	assert(window->frame_id != XCB_WINDOW_NONE);
+
+	property[0] = allow ? 1 : 0;
+
+	xcb_change_property(wm->conn,
+			    XCB_PROP_MODE_REPLACE,
+			    window->frame_id,
+			    wm->atom.allow_commits,
+			    XCB_ATOM_CARDINAL,
+			    32, /* format */
+			    1, property);
+}
+
 #define ICCCM_WITHDRAWN_STATE	0
 #define ICCCM_NORMAL_STATE	1
 #define ICCCM_ICONIC_STATE	3
@@ -1048,6 +1079,7 @@ weston_wm_handle_map_request(struct weston_wm *wm, xcb_generic_event_t *event)
 	       window->width, window->height,
 	       window->map_request_x, window->map_request_y);
 
+	weston_wm_window_set_allow_commits(window, false);
 	weston_wm_window_set_wm_state(window, ICCCM_NORMAL_STATE);
 	weston_wm_window_set_net_wm_state(window);
 	weston_wm_window_set_virtual_desktop(window, 0);
@@ -2220,6 +2252,7 @@ weston_wm_get_resources(struct weston_wm *wm)
 		{ "XdndFinished",	F(atom.xdnd_finished) },
 		{ "XdndTypeList",	F(atom.xdnd_type_list) },
 		{ "XdndActionCopy",	F(atom.xdnd_action_copy) },
+		{ "_XWAYLAND_ALLOW_COMMITS",	F(atom.allow_commits) },
 		{ "WL_SURFACE_ID",	F(atom.wl_surface_id) }
 	};
 #undef F
@@ -2741,10 +2774,13 @@ xserver_map_shell_surface(struct weston_wm_window *window,
 		}
 	}
 
-	if (window->frame_id == XCB_WINDOW_NONE)
+	if (window->frame_id == XCB_WINDOW_NONE) {
 		weston_wm_window_set_pending_state_OR(window);
-	else
+	} else {
 		weston_wm_window_set_pending_state(window);
+		weston_wm_window_set_allow_commits(window, true);
+		xcb_flush(wm->conn);
+	}
 }
 
 const struct weston_xwayland_surface_api surface_api = {

xwayland/xwayland.h

@@ -154,6 +154,7 @@ struct weston_wm {
 		xcb_atom_t		 xdnd_type_list;
 		xcb_atom_t		 xdnd_action_copy;
 		xcb_atom_t		 wl_surface_id;
+		xcb_atom_t		 allow_commits;
 	} atom;
 };