cursor: process layer subsurfaces in cursor_button_press()

...to give keyboard focus to layer-shell clients if exclusive or on-demand
interactivity is set, so that menu popups can be navigated with the
keyboard. This still only works if the client is in top (or overlay)
layers. Support for bottom and background to be done as a separate patch
set.

Revert 06b19f0 to process layer-shell subsurfaces in
`cursor_button_press()`, but only when their parent layer-shell surface
has keyboard interactivity.

Fix bug in `get_cursor_context()` which resulted in layer-surfaces not
being detected correctly.

Background:

Commit 06b19f0 (issue #1131) disabled processing of layer-shell
subsurfaces in cursor_button_press() because when pressing a task in
Waybar (Gtk panel using layer-shell subsurfaces) the foreign-toplevel
minimize-raise action did not work correctly as the action logic relied on
the recipient window being activated and by clicking on the panel, the
panel itself was both surface-focusd and activated (and thus the window
de-activated).

The un-intended consequence was that by not responding to layer-subsurface
cursor buttons presses, layer-shell clients (such as panels) were not
given keyboard focus if they indeed wanted it by setting exclusive or
on-demand keyboard interactivity.

The good news is that that following @jlindgren90's refactoring (various)
the only place where we call `view_set_actived()` is in
`focus_change_notify()` in `seat.c` and we now only do it for views
(bb8f0bc).

Another side-effect (positive) of 06b19f0 was that a Waybar dnd bug was
fixed (pointer-serial-number validation failure).

Have tested with sfwbar, waybar and tint (test-panel) the following
results:
- Minimize-raise works even when on-demand keyboard interactivity is set
- Keyboard interactivity is given popup-menus (sfwbar and tint) when the
  panels are in the top layer (support for bottom will be as a separate
  patch set)
- Waybar dnd still works (even when hard-coding keyboard-interactivity)

References:
- bb8f0bc960
- 40ce95a68c/src/seat.c (L481-L483)
- 40ce95a68c/src/dnd.c (L24)
- https://github.com/johanmalm/tint

Fixes: #1572

include/common/surface-helpers.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LABWC_SURFACE_HELPERS_H
+#define LABWC_SURFACE_HELPERS_H
+
+struct wlr_surface;
+struct wlr_layer_surface_v1;
+
+/**
+ * subsurface_parent_layer() - Get wlr_layer_surface from layer-subsurface
+ * @wlr_surface: The wlr_surface of the wlr_subsurface for which to get the
+ *               layer-surface.
+ */
+struct wlr_layer_surface_v1 *subsurface_parent_layer(
+	struct wlr_surface *wlr_surface);
+
+#endif /* LABWC_SURFACE_HELPERS_H */

src/common/meson.build

@@ -13,6 +13,7 @@ labwc_sources += files(
   'scaled_font_buffer.c',
   'scaled_scene_buffer.c',
   'scene-helpers.c',
+  'surface-helpers.c',
   'spawn.c',
   'string-helpers.c',
 )

src/common/surface-helpers.c

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <wlr/types/wlr_layer_shell_v1.h>
+#include <wlr/types/wlr_subcompositor.h>
+#include <wlr/util/log.h>
+#include "common/surface-helpers.h"
+
+struct wlr_layer_surface_v1 *
+subsurface_parent_layer(struct wlr_surface *wlr_surface)
+{
+	struct wlr_subsurface *subsurface =
+		wlr_subsurface_try_from_wlr_surface(wlr_surface);
+	if (!subsurface) {
+		wlr_log(WLR_DEBUG, "surface %p is not subsurface", subsurface);
+		return NULL;
+	}
+	struct wlr_surface *parent = subsurface->parent;
+	if (!parent) {
+		wlr_log(WLR_DEBUG, "subsurface %p has no parent", subsurface);
+		return NULL;
+	}
+	struct wlr_layer_surface_v1 *wlr_layer_surface =
+		wlr_layer_surface_v1_try_from_wlr_surface(parent);
+	if (wlr_layer_surface) {
+		return wlr_layer_surface;
+	}
+	/* Recurse in case there are nested sub-surfaces */
+	return subsurface_parent_layer(parent);
+}

src/desktop.c

@@ -2,6 +2,7 @@
 #include "config.h"
 #include <assert.h>
 #include "common/scene-helpers.h"
+#include "common/surface-helpers.h"
 #include "dnd.h"
 #include "labwc.h"
 #include "layers.h"
@@ -255,21 +256,6 @@ get_surface_from_layer_node(struct wlr_scene_node *node)
 	return NULL;
 }
 
-static bool
-is_layer_descendant(struct wlr_scene_node *node)
-{
-	goto start;
-	while (node) {
-		struct node_descriptor *desc = node->data;
-		if (desc && desc->type == LAB_NODE_DESC_LAYER_SURFACE) {
-			return true;
-		}
-start:
-		node = node->parent ? &node->parent->node : NULL;
-	}
-	return false;
-}
-
 /* TODO: make this less big and scary */
 struct cursor_context
 get_cursor_context(struct server *server)
@@ -354,24 +340,23 @@ get_cursor_context(struct server *server)
 		/* Edge-case nodes without node-descriptors */
 		if (node->type == WLR_SCENE_NODE_BUFFER) {
 			struct wlr_surface *surface = lab_wlr_surface_from_node(node);
-			if (surface) {
-				if (wlr_layer_surface_v1_try_from_wlr_surface(surface)) {
-					ret.type = LAB_SSD_LAYER_SURFACE;
-				}
-				if (is_layer_descendant(node)) {
-					/*
-					 * layer-shell subsurfaces need to be
-					 * able to receive pointer actions.
-					 *
-					 * Test by running
-					 * `gtk-layer-demo -k exclusive`, then
-					 * open the 'set margin' dialog and try
-					 * setting the margin with the pointer.
-					 */
-					ret.surface = surface;
-					ret.type = LAB_SSD_LAYER_SUBSURFACE;
-					return ret;
-				}
+
+			/*
+			 * Handle layer-shell subsurfaces
+			 *
+			 * These don't have node-descriptors, but need to be
+			 * able to receive pointer actions so we have to process
+			 * them here.
+			 *
+			 * Test by running `gtk-layer-demo -k exclusive`, then
+			 * open the 'set margin' dialog and try setting the
+			 * margin with the pointer.
+			 */
+			if (surface && wlr_subsurface_try_from_wlr_surface(surface)
+					&& subsurface_parent_layer(surface)) {
+				ret.surface = surface;
+				ret.type = LAB_SSD_LAYER_SUBSURFACE;
+				return ret;
 			}
 		}
 

src/input/cursor.c

@@ -11,6 +11,7 @@
 #include "common/macros.h"
 #include "common/mem.h"
 #include "common/scene-helpers.h"
+#include "common/surface-helpers.h"
 #include "config/mousebind.h"
 #include "dnd.h"
 #include "idle.h"
@@ -965,11 +966,19 @@ cursor_button_press(struct seat *seat, uint32_t button,
 	 * the Focus action (used for normal views) does not work.
 	 */
 	if (ctx.type == LAB_SSD_LAYER_SURFACE) {
+		wlr_log(WLR_DEBUG, "press on layer-surface");
 		struct wlr_layer_surface_v1 *layer =
 			wlr_layer_surface_v1_try_from_wlr_surface(ctx.surface);
 		if (layer && layer->current.keyboard_interactive) {
 			seat_set_focus_layer(seat, layer);
 		}
+	} else if (ctx.type == LAB_SSD_LAYER_SUBSURFACE) {
+		wlr_log(WLR_DEBUG, "press on layer-subsurface");
+		struct wlr_layer_surface_v1 *layer =
+			subsurface_parent_layer(ctx.surface);
+		if (layer && layer->current.keyboard_interactive) {
+			seat_set_focus_layer(seat, layer);
+		}
 #ifdef HAVE_XWAYLAND
 	} else if (ctx.type == LAB_SSD_UNMANAGED) {
 		desktop_focus_view_or_surface(seat, NULL, ctx.surface,
@@ -977,12 +986,6 @@ cursor_button_press(struct seat *seat, uint32_t button,
 #endif
 	}
 
-	/*
-	 * TODO: We may need to handle press on layer-shell subsurfaces here,
-	 * but need to check keyboard interactivity before focusing them
-	 * otherwise we break waybar. See issue #1131
-	 */
-
 	if (ctx.type != LAB_SSD_CLIENT && ctx.type != LAB_SSD_LAYER_SUBSURFACE
 			&& wlr_seat_pointer_has_grab(seat->seat)) {
 		/*