Add tearing support (#1390)

Co-authored-by: Andrew J. Hesford <ajh@sideband.org>

docs/labwc-actions.5.scd

@@ -154,6 +154,9 @@ Actions are used in menus and keyboard/mouse bindings.
 	the usual keybinds will function again until switching back to the
 	original window. There can be multiple windows with this mode set.
 
+*<action name="ToggleTearing" />*
+	Toggles tearing for the focused window.
+
 *<action name="FocusOutput" output="HDMI-A-1" />*
 	Give focus to topmost window on given output and warp the cursor
 	to the center of the window. If the given output does not contain

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 +129,12 @@ this is for compatibility with Openbox.
 	*fullscreen* enables adaptive sync whenever a window is in fullscreen
 	mode.
 
+*<core><allowTearing>* [yes|no]
+	Allow tearing to reduce input lag. Default is no.
+	This option requires setting the environment variable WLR_DRM_NO_ATOMIC=1.
+
+	*yes* allow tearing if requested by the active window.
+
 *<core><reuseOutputMode>* [yes|no]
 	Try to re-use the existing output mode (resolution / refresh rate).
 	This may prevent unnecessary screenblank delays when starting labwc

docs/rc.xml.all

@@ -11,6 +11,7 @@
     <decoration>server</decoration>
     <gap>0</gap>
     <adaptiveSync>no</adaptiveSync>
+    <allowTearing>no</allowTearing>
     <reuseOutputMode>no</reuseOutputMode>
   </core>
 

include/config/rcxml.h

@@ -53,6 +53,7 @@ struct rcxml {
 	bool xdg_shell_server_side_deco;
 	int gap;
 	enum adaptive_sync_mode adaptive_sync;
+	bool allow_tearing;
 	bool reuse_output_mode;
 	enum view_placement_policy placement_policy;
 

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;
@@ -478,6 +482,7 @@ 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 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/action.c

@@ -102,6 +102,7 @@ enum action_type {
 	ACTION_TYPE_VIRTUAL_OUTPUT_ADD,
 	ACTION_TYPE_VIRTUAL_OUTPUT_REMOVE,
 	ACTION_TYPE_AUTO_PLACE,
+	ACTION_TYPE_TOGGLE_TEARING,
 };
 
 const char *action_names[] = {
@@ -149,6 +150,7 @@ const char *action_names[] = {
 	"VirtualOutputAdd",
 	"VirtualOutputRemove",
 	"AutoPlace",
+	"ToggleTearing",
 	NULL
 };
 
@@ -951,6 +953,13 @@ actions_run(struct view *activator, struct server *server,
 				}
 			}
 			break;
+		case ACTION_TYPE_TOGGLE_TEARING:
+			if (view) {
+				view->tearing_hint = !view->tearing_hint;
+				wlr_log(WLR_DEBUG, "tearing %sabled",
+					view->tearing_hint ? "en" : "dis");
+			}
+			break;
 		case ACTION_TYPE_INVALID:
 			wlr_log(WLR_ERROR, "Not executing unknown action");
 			break;

src/config/rcxml.c

@@ -740,6 +740,12 @@ entry(xmlNode *node, char *nodename, char *content)
 		rc.gap = atoi(content);
 	} else if (!strcasecmp(nodename, "adaptiveSync.core")) {
 		set_adaptive_sync_mode(content, &rc.adaptive_sync);
+	} else if (!strcasecmp(nodename, "allowTearing.core")) {
+		set_bool(content, &rc.allow_tearing);
+		if (rc.allow_tearing && strcmp(getenv("WLR_DRM_NO_ATOMIC"), "1")) {
+			rc.allow_tearing = false;
+			wlr_log(WLR_INFO, "WLR_DRM_NO_ATOMIC is not 1, tearing disabled");
+		}
 	} else if (!strcasecmp(nodename, "reuseOutputMode.core")) {
 		set_bool(content, &rc.reuse_output_mode);
 	} else if (!strcmp(nodename, "policy.placement")) {

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

@@ -27,6 +27,25 @@
 #include "view.h"
 #include "xwayland.h"
 
+static bool
+get_tearing_preference(struct output *output)
+{
+	struct server *server = output->server;
+
+	/* Never allow tearing when disabled */
+	if (!rc.allow_tearing) {
+		return false;
+	}
+
+	/* Tearing is only allowed for the output with the active view */
+	if (!server->active_view || server->active_view->output != output) {
+		return false;
+	}
+
+	/* If the active view requests tearing, or it is toggled on with action, allow it */
+	return server->active_view->tearing_hint;
+}
+
 static void
 output_frame_notify(struct wl_listener *listener, void *data)
 {
@@ -68,7 +87,9 @@ output_frame_notify(struct wl_listener *listener, void *data)
 		return;
 	}
 
-	wlr_scene_output_commit(output->scene_output, NULL);
+	output->wlr_output->pending.tearing_page_flip =
+		get_tearing_preference(output);
+	lab_wlr_scene_output_commit(output->scene_output);
 
 	struct timespec now = { 0 };
 	clock_gettime(CLOCK_MONOTONIC, &now);

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 +1,50 @@
+// 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 && controller->tearing_control->hint) {
+		view->tearing_hint = true;
+	}
+}
+
+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);
+}