tearing protocol support and documentation

docs/labwc-config.5.scd

@@ -109,6 +109,7 @@ this is for compatibility with Openbox.
   <decoration>server</decoration>
   <gap>0</gap>
   <adaptiveSync>no</adaptiveSync>
+  <allowTearing>no</allowTearing>
   <reuseOutputMode>no</reuseOutputMode>
 </core>
 ```
@@ -128,6 +129,17 @@ this is for compatibility with Openbox.
 	*fullscreen* enables adaptive sync whenever a window is in fullscreen
 	mode.
 
+*<core><allowTearing>* [yes|no|fullscreen|always]
+	Allow tearing to reduce input lag. Default is no.
+	This open requires setting the environment variable WLR_DRM_NO_ATOMIC=1.
+
+	*yes* allow tearing if an open window requests it.
+
+	*fullscreen* allow tearing if an open window requests it, or if any
+	window is in fullscreen mode.
+
+	*always* allow tearing regardless of window status.
+
 *<core><reuseOutputMode>* [yes|no]
 	Try to re-use the existing output mode (resolution / refresh rate).
 	This may prevent unnecessary screenblank delays when starting labwc

include/config/rcxml.h

@@ -38,6 +38,7 @@ enum tearing_mode {
 	LAB_TEARING_DISABLED,
 	LAB_TEARING_ENABLED,
 	LAB_TEARING_FULLSCREEN,
+	LAB_TEARING_ALWAYS,
 };
 
 struct usable_area_override {

include/labwc.h

@@ -39,6 +39,7 @@
 #include <wlr/types/wlr_drm_lease_v1.h>
 #include <wlr/types/wlr_virtual_pointer_v1.h>
 #include <wlr/types/wlr_virtual_keyboard_v1.h>
+#include <wlr/types/wlr_tearing_control_v1.h>
 #include <wlr/util/log.h>
 #include "config/keybind.h"
 #include "config/rcxml.h"
@@ -318,6 +319,9 @@ struct server {
 	struct wlr_pointer_constraints_v1 *constraints;
 	struct wl_listener new_constraint;
 
+	struct wlr_tearing_control_manager_v1 *tearing_control;
+	struct wl_listener tearing_new_object;
+
 	/* Set when in cycle (alt-tab) mode */
 	struct osd_state {
 		struct view *cycle_view;
@@ -479,6 +483,8 @@ void handle_output_power_manager_set_mode(struct wl_listener *listener,
 void output_add_virtual(struct server *server, const char *output_name);
 void output_remove_virtual(struct server *server, const char *output_name);
 void output_enable_adaptive_sync(struct wlr_output *output, bool enabled);
+void new_tearing_hint(struct wl_listener *listener, void *data);
+void set_tearing(struct output *output);
 
 void server_init(struct server *server);
 void server_start(struct server *server);

include/view.h

@@ -151,6 +151,7 @@ struct view {
 	bool minimized;
 	enum view_axis maximized;
 	bool fullscreen;
+	bool tearing_hint;
 	bool visible_on_all_workspaces;
 	enum view_edge tiled;
 	bool inhibits_keybinds;

protocols/meson.build

@@ -18,6 +18,7 @@ server_protocols = [
 	wl_protocol_dir / 'unstable/pointer-constraints/pointer-constraints-unstable-v1.xml',
 	wl_protocol_dir / 'staging/cursor-shape/cursor-shape-v1.xml',
 	wl_protocol_dir / 'staging/drm-lease/drm-lease-v1.xml',
+	wl_protocol_dir / 'staging/tearing-control/tearing-control-v1.xml',
 	'wlr-layer-shell-unstable-v1.xml',
 	'wlr-input-inhibitor-unstable-v1.xml',
 	'wlr-output-power-management-unstable-v1.xml',

src/config/rcxml.c

@@ -630,6 +630,8 @@ set_tearing_mode(const char *str, enum tearing_mode *variable)
 {
 	if (!strcasecmp(str, "fullscreen")) {
 		*variable = LAB_TEARING_FULLSCREEN;
+	} else if (!strcasecmp(str, "always"))	{
+		*variable = LAB_TEARING_ALWAYS;
 	} else {
 		int ret = parse_bool(str, -1);
 		if (ret == 1) {

src/meson.build

@@ -19,6 +19,7 @@ labwc_sources = files(
   'server.c',
   'session-lock.c',
   'snap.c',
+  'tearing.c',
   'theme.c',
   'view.c',
   'view-impl-common.c',

src/output.c

@@ -68,9 +68,7 @@ output_frame_notify(struct wl_listener *listener, void *data)
 		return;
 	}
 
-	if (output->tearing) {
-		output->wlr_output->pending.tearing_page_flip = true;
-	}
+	output->wlr_output->pending.tearing_page_flip = output->tearing;
 
 	lab_wlr_scene_output_commit(output->scene_output);
 
@@ -277,7 +275,7 @@ new_output_notify(struct wl_listener *listener, void *data)
 
 	wl_list_init(&output->regions);
 
-	if (rc.allow_tearing == LAB_TEARING_ENABLED) {
+	if (rc.allow_tearing == LAB_TEARING_ALWAYS) {
 		output->tearing = true;
 	} else {
 		output->tearing = false;

src/server.c

@@ -449,6 +449,10 @@ server_init(struct server *server)
 	wl_signal_add(&server->output_power_manager_v1->events.set_mode,
 		&server->output_power_manager_set_mode);
 
+	server->tearing_control = wlr_tearing_control_manager_v1_create(server->wl_display, 1);
+	server->tearing_new_object.notify = new_tearing_hint;
+	wl_signal_add(&server->tearing_control->events.new_object, &server->tearing_new_object);
+
 	layers_init(server);
 
 #if HAVE_XWAYLAND

src/tearing.c

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "labwc.h"
+#include "view.h"
+
+struct tearing_controller {
+		struct wlr_tearing_control_v1 *tearing_control;
+		struct wl_listener set_hint;
+		struct wl_listener destroy;
+};
+
+static void
+set_tearing_hint(struct wl_listener *listener, void *data)
+{
+	struct tearing_controller *controller = wl_container_of(listener, controller, set_hint);
+	struct view *view = view_from_wlr_surface(controller->tearing_control->surface);
+	if (view) {
+		view->tearing_hint = controller->tearing_control->hint;
+	}
+}
+
+static void
+tearing_controller_destroy(struct wl_listener *listener, void *data)
+{
+	struct tearing_controller *controller = wl_container_of(listener, controller, destroy);
+	free(controller);
+}
+
+void
+new_tearing_hint(struct wl_listener *listener, void *data)
+{
+	struct server *server = wl_container_of(listener, server, tearing_new_object);
+	struct wlr_tearing_control_v1 *tearing_control = data;
+
+	enum wp_tearing_control_v1_presentation_hint hint =
+		wlr_tearing_control_manager_v1_surface_hint_from_surface
+		(server->tearing_control, tearing_control->surface);
+	wlr_log(WLR_DEBUG, "New presentation hint %d received for surface %p",
+		hint, tearing_control->surface);
+
+	struct tearing_controller *controller = calloc(1, sizeof(struct tearing_controller));
+	if (!controller) {
+		return;
+	}
+	controller->tearing_control = tearing_control;
+	controller->set_hint.notify = set_tearing_hint;
+	wl_signal_add(&tearing_control->events.set_hint, &controller->set_hint);
+	controller->destroy.notify = tearing_controller_destroy;
+	wl_signal_add(&tearing_control->events.destroy, &controller->destroy);
+}
+
+void
+set_tearing(struct output *output)
+{
+	if (rc.allow_tearing == LAB_TEARING_DISABLED) {
+		output->tearing = false;
+		return;
+	}
+
+	if (rc.allow_tearing == LAB_TEARING_ALWAYS) {
+		output->tearing = true;
+		return;
+	}
+
+	struct server *server = output->server;
+	struct view *view;
+	bool on_fullscreen = rc.allow_tearing == LAB_TEARING_FULLSCREEN;
+
+	wl_list_for_each(view, &server->views, link) {
+		if (view->output != output) {
+			continue;
+		}
+
+		if (view->tearing_hint || (on_fullscreen && view->fullscreen)) {
+			output->tearing = true;
+			return;
+		}
+	}
+	output->tearing = false;
+}

src/view.c

@@ -273,16 +273,6 @@ set_adaptive_sync_fullscreen(struct view *view)
 	wlr_output_commit(view->output->wlr_output);
 }
 
-static void
-set_tearing_fullscreen(struct view *view)
-{
-	if (rc.allow_tearing != LAB_TEARING_FULLSCREEN) {
-		return;
-	}
-	/* Enable tearing if view is fullscreen */
-	view->output->tearing = view->fullscreen;
-}
-
 void
 view_set_activated(struct view *view, bool activated)
 {
@@ -307,7 +297,7 @@ view_set_activated(struct view *view, bool activated)
 		}
 	}
 	set_adaptive_sync_fullscreen(view);
-	set_tearing_fullscreen(view);
+	set_tearing(view->output);
 }
 
 void
@@ -1210,7 +1200,7 @@ view_set_fullscreen(struct view *view, bool fullscreen)
 		view_apply_special_geometry(view);
 	}
 	set_adaptive_sync_fullscreen(view);
-	set_tearing_fullscreen(view);
+	set_tearing(view->output);
 }
 
 void
@@ -1881,9 +1871,6 @@ view_destroy(struct view *view)
 		if (rc.adaptive_sync == LAB_ADAPTIVE_SYNC_FULLSCREEN) {
 			wlr_output_enable_adaptive_sync(view->output->wlr_output, false);
 		}
-		if (rc.allow_tearing == LAB_TEARING_FULLSCREEN) {
-			view->output->tearing = false;
-		}
 	}
 
 	/* If we spawned a window menu, close it */