patch

wlroots.patch

diff --git a/include/util/time.h b/include/util/time.h
index dd164bf2..fd2bf962 100644
--- a/include/util/time.h
+++ b/include/util/time.h
@@ -6,6 +6,11 @@
 
 static const long NSEC_PER_SEC = 1000000000;
 
+/**
+ * Get the current time, in nanoseconds.
+ */
+int64_t get_current_time_nsec(void);
+
 /**
  * Get the current time, in milliseconds.
  */
diff --git a/include/wlr/types/wlr_fifo_v1.h b/include/wlr/types/wlr_fifo_v1.h
new file mode 100644
index 00000000..4ea9c18a
--- /dev/null
+++ b/include/wlr/types/wlr_fifo_v1.h
@@ -0,0 +1,107 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_TYPES_WLR_FIFO_V1_H
+#define WLR_TYPES_WLR_FIFO_V1_H
+
+#include <wayland-server-core.h>
+
+#include <wlr/types/wlr_compositor.h>
+#include <wlr/types/wlr_scene.h>
+
+struct wlr_fifo_manager_v1_new_fifo_event {
+	struct wlr_fifo_v1 *fifo;
+};
+
+struct wlr_fifo_manager_v1 {
+	struct wl_global *global;
+	struct wl_display *display;
+
+	struct {
+		struct wl_signal new_fifo; // struct wlr_fifo_manager_v1_new_fifo_event
+
+		/**
+		 * Signals that the fifo manager is being destroyed.
+		 */
+		struct wl_signal destroy;
+	} events;
+
+	struct {
+		struct wl_listener display_destroy;
+	} WLR_PRIVATE;
+};
+
+struct wlr_fifo_v1_state {
+	/*
+	 * This field is used to set the fifo barrier on the surface.
+	 * Set when the client makes a .set_barrier request. */
+	bool set_barrier;
+	/*
+	 * This field is used to lock a commit until the fifo barrier on the surface is cleared.
+	 * Set when the client makes a .wait_barrier request. */
+	bool wait_barrier;
+};
+
+struct wlr_fifo_v1 {
+	struct wlr_fifo_manager_v1 *manager;
+
+	struct wl_resource *resource;
+	struct wlr_addon addon;
+
+	struct wlr_surface *surface;
+	struct wlr_output *output;
+
+	// list of commit requests waiting on the fifo barrier
+	struct wl_list commits; // fifo_commit.link
+
+	// per-commit state used with the wlr_surface_synced mechanism
+	struct wlr_fifo_v1_state current, pending;
+
+	// per-wlr_fifo_v1 instance state
+	bool barrier_set;
+	uint64_t last_output_present_nsec;
+	bool surface_occluded_source_armed;
+
+	struct {
+		/**
+		 * Signals that the fifo object is being destroyed.
+		 */
+		struct wl_signal destroy;
+	} events;
+
+	struct {
+		struct wl_listener surface_client_commit;
+		struct wl_listener surface_commit;
+		struct wl_listener output_present;
+		struct wl_listener output_destroy;
+		struct wl_listener fifo_manager_destroy;
+
+		// used to advance the queue when the surface is occluded
+		struct wl_event_source *surface_occluded_source;
+
+		struct wlr_surface_synced synced;
+	} WLR_PRIVATE;
+
+	struct wl_list link; // wlr_scene.fifo_surfaces
+};
+
+/**
+ * Create the wp_fifo_manager_v1_interface global, which can be used by clients to
+ * queue commits on a wl_surface for presentation.
+ */
+struct wlr_fifo_manager_v1 *wlr_fifo_manager_v1_create(struct wl_display *display,
+	uint32_t version);
+
+/**
+ * Used to set the output to which the fifo will be applied.
+ * If output is NULL, the fifo will be unset for a previously set output.
+ * Returns true on success, false on failure.
+ */
+void wlr_fifo_v1_set_output(struct wlr_fifo_v1 *fifo, struct wlr_output *output);
+
+#endif
diff --git a/include/wlr/types/wlr_scene.h b/include/wlr/types/wlr_scene.h
index 6c627b1f..a40204f5 100644
--- a/include/wlr/types/wlr_scene.h
+++ b/include/wlr/types/wlr_scene.h
@@ -104,6 +104,7 @@ struct wlr_scene {
 	struct wlr_linux_dmabuf_v1 *linux_dmabuf_v1;
 	struct wlr_gamma_control_manager_v1 *gamma_control_manager_v1;
 	struct wlr_color_manager_v1 *color_manager_v1;
+	struct wlr_fifo_manager_v1 *fifo_manager_v1;
 
 	bool restack_xwayland_surfaces;
 
@@ -112,6 +113,8 @@ struct wlr_scene {
 		struct wl_listener gamma_control_manager_v1_destroy;
 		struct wl_listener gamma_control_manager_v1_set_gamma;
 		struct wl_listener color_manager_v1_destroy;
+		struct wl_listener fifo_manager_v1_destroy;
+		struct wl_listener fifo_manager_v1_new_fifo;
 
 		enum wlr_scene_debug_damage_option debug_damage_option;
 		bool direct_scanout;
@@ -125,6 +128,8 @@ struct wlr_scene_surface {
 	struct wlr_scene_buffer *buffer;
 	struct wlr_surface *surface;
 
+	struct wlr_fifo_v1 *fifo;
+
 	struct {
 		struct wlr_box clip;
 
@@ -135,6 +140,7 @@ struct wlr_scene_surface {
 		struct wl_listener frame_done;
 		struct wl_listener surface_destroy;
 		struct wl_listener surface_commit;
+		struct wl_listener fifo_v1_destroy;
 	} WLR_PRIVATE;
 };
 
@@ -383,6 +389,12 @@ void wlr_scene_set_gamma_control_manager_v1(struct wlr_scene *scene,
  */
 void wlr_scene_set_color_manager_v1(struct wlr_scene *scene, struct wlr_color_manager_v1 *manager);
 
+/**
+ * Handles fifo_v1 for all surfaces and their primary outputs in the scene.
+ */
+void wlr_scene_set_fifo_manager_v1(struct wlr_scene *scene,
+	struct wlr_fifo_manager_v1 *fifo_manager);
+
 /**
  * Add a node displaying nothing but its children.
  */
diff --git a/protocol/meson.build b/protocol/meson.build
index 30aeb68c..eb8ca605 100644
--- a/protocol/meson.build
+++ b/protocol/meson.build
@@ -37,6 +37,7 @@ protocols = {
 	'ext-session-lock-v1': wl_protocol_dir / 'staging/ext-session-lock/ext-session-lock-v1.xml',
 	'ext-data-control-v1': wl_protocol_dir / 'staging/ext-data-control/ext-data-control-v1.xml',
 	'ext-workspace-v1': wl_protocol_dir / 'staging/ext-workspace/ext-workspace-v1.xml',
+	'fifo-v1': wl_protocol_dir / 'staging/fifo/fifo-v1.xml',
 	'fractional-scale-v1': wl_protocol_dir / 'staging/fractional-scale/fractional-scale-v1.xml',
 	'linux-drm-syncobj-v1': wl_protocol_dir / 'staging/linux-drm-syncobj/linux-drm-syncobj-v1.xml',
 	'security-context-v1': wl_protocol_dir / 'staging/security-context/security-context-v1.xml',
diff --git a/types/meson.build b/types/meson.build
index 26958f04..bd29ac42 100644
--- a/types/meson.build
+++ b/types/meson.build
@@ -77,6 +77,7 @@ wlr_files += files(
 	'wlr_presentation_time.c',
 	'wlr_primary_selection_v1.c',
 	'wlr_primary_selection.c',
+	'wlr_fifo_v1.c',
 	'wlr_region.c',
 	'wlr_relative_pointer_v1.c',
 	'wlr_screencopy_v1.c',
diff --git a/types/scene/surface.c b/types/scene/surface.c
index 89c54a9e..bbce19b7 100644
--- a/types/scene/surface.c
+++ b/types/scene/surface.c
@@ -5,6 +5,7 @@
 #include <wlr/types/wlr_color_representation_v1.h>
 #include <wlr/types/wlr_compositor.h>
 #include <wlr/types/wlr_scene.h>
+#include <wlr/types/wlr_fifo_v1.h>
 #include <wlr/types/wlr_fractional_scale_v1.h>
 #include <wlr/types/wlr_linux_drm_syncobj_v1.h>
 #include <wlr/types/wlr_output.h>
@@ -134,6 +135,9 @@ static void handle_scene_buffer_outputs_update(
 
 	// No reason to update the preferred configuration if we aren't sending leave/enter events.
 	if (suspend) {
+		if (surface->fifo) {
+			wlr_fifo_v1_set_output(surface->fifo, NULL);
+		}
 		return;
 	}
 
@@ -153,6 +157,9 @@ static void handle_scene_buffer_outputs_update(
 		wlr_color_manager_v1_set_surface_preferred_image_description(scene->color_manager_v1,
 			surface->surface, &img_desc);
 	}
+	if (surface->fifo) {
+		wlr_fifo_v1_set_output(surface->fifo, surface->buffer->primary_output->output);
+	}
 }
 
 static void handle_scene_buffer_output_sample(
diff --git a/types/scene/wlr_scene.c b/types/scene/wlr_scene.c
index 54c09bbf..62c44330 100644
--- a/types/scene/wlr_scene.c
+++ b/types/scene/wlr_scene.c
@@ -8,6 +8,7 @@
 #include <wlr/types/wlr_color_management_v1.h>
 #include <wlr/types/wlr_compositor.h>
 #include <wlr/types/wlr_damage_ring.h>
+#include <wlr/types/wlr_fifo_v1.h>
 #include <wlr/types/wlr_gamma_control_v1.h>
 #include <wlr/types/wlr_linux_dmabuf_v1.h>
 #include <wlr/types/wlr_presentation_time.h>
@@ -1655,6 +1656,72 @@ void wlr_scene_set_color_manager_v1(struct wlr_scene *scene, struct wlr_color_ma
 	wl_signal_add(&manager->events.destroy, &scene->color_manager_v1_destroy);
 }
 
+static void scene_surface_handle_fifo_v1_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene_surface *surface =
+		wl_container_of(listener, surface, fifo_v1_destroy);
+	wl_list_remove(&surface->fifo_v1_destroy.link);
+	surface->fifo = NULL;
+}
+
+static void scene_fifo_set_output(struct wlr_scene_node *node, struct wlr_fifo_v1 *fifo) {
+	if (node->type == WLR_SCENE_NODE_TREE) {
+		struct wlr_scene_tree *scene_tree = wlr_scene_tree_from_node(node);
+		struct wlr_scene_node *child;
+		wl_list_for_each(child, &scene_tree->children, link) {
+			scene_fifo_set_output(child, fifo);
+		}
+	}
+	if (node->type != WLR_SCENE_NODE_BUFFER) {
+		return;
+	}
+
+	struct wlr_scene_buffer *scene_buffer = wlr_scene_buffer_from_node(node);
+	struct wlr_scene_surface *scene_surface =
+		wlr_scene_surface_try_from_buffer(scene_buffer);
+	if (!scene_surface) {
+		return;
+	}
+
+	if (scene_surface->surface == fifo->surface) {
+		scene_surface->fifo = fifo;
+		scene_surface->fifo_v1_destroy.notify = scene_surface_handle_fifo_v1_destroy;
+		wl_signal_add(&fifo->events.destroy, &scene_surface->fifo_v1_destroy);
+		wlr_fifo_v1_set_output(fifo, scene_buffer->primary_output ?
+			scene_buffer->primary_output->output : NULL);
+	}
+}
+
+static void scene_handle_fifo_manager_v1_new_fifo(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene *scene =
+		wl_container_of(listener, scene, fifo_manager_v1_new_fifo);
+	struct wlr_fifo_manager_v1_new_fifo_event *event = data;
+
+	scene_fifo_set_output(&scene->tree.node, event->fifo);
+}
+
+static void scene_handle_fifo_manager_v1_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene *scene =
+		wl_container_of(listener, scene, fifo_manager_v1_destroy);
+	wl_list_remove(&scene->fifo_manager_v1_destroy.link);
+	wl_list_init(&scene->fifo_manager_v1_destroy.link);
+	wl_list_remove(&scene->fifo_manager_v1_new_fifo.link);
+	wl_list_init(&scene->fifo_manager_v1_new_fifo.link);
+	scene->fifo_manager_v1 = NULL;
+}
+
+void wlr_scene_set_fifo_manager_v1(struct wlr_scene *scene,
+	    struct wlr_fifo_manager_v1 *fifo_manager) {
+	assert(scene->fifo_manager_v1 == NULL);
+	scene->fifo_manager_v1 = fifo_manager;
+	scene->fifo_manager_v1_new_fifo.notify = scene_handle_fifo_manager_v1_new_fifo;
+	wl_signal_add(&fifo_manager->events.new_fifo, &scene->fifo_manager_v1_new_fifo);
+	scene->fifo_manager_v1_destroy.notify = scene_handle_fifo_manager_v1_destroy;
+	wl_signal_add(&fifo_manager->events.destroy, &scene->fifo_manager_v1_destroy);
+}
+
 static void scene_output_handle_destroy(struct wlr_addon *addon) {
 	struct wlr_scene_output *scene_output =
 		wl_container_of(addon, scene_output, addon);
diff --git a/types/wlr_fifo_v1.c b/types/wlr_fifo_v1.c
new file mode 100644
index 00000000..31bb2cad
--- /dev/null
+++ b/types/wlr_fifo_v1.c
@@ -0,0 +1,363 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <wlr/types/wlr_compositor.h>
+#include <wlr/types/wlr_output.h>
+#include <wlr/types/wlr_fifo_v1.h>
+#include <wlr/util/log.h>
+#include "fifo-v1-protocol.h"
+#include "util/time.h"
+
+#define FIFO_MANAGER_VERSION 1
+
+struct fifo_commit {
+	struct wlr_fifo_v1 *fifo;
+	struct wl_list link; // wlr_fifo_v1.fifo_commits
+	bool barrier_pending;
+	uint32_t seq;
+};
+
+static void surface_synced_move_state(void *_dst, void *_src) {
+	struct wlr_fifo_v1_state *dst = _dst, *src = _src;
+	dst->set_barrier = src->set_barrier;
+	dst->wait_barrier = src->wait_barrier;
+	src->wait_barrier = false;
+	src->set_barrier = false;
+}
+
+static const struct wlr_surface_synced_impl surface_synced_impl = {
+	.state_size = sizeof(struct wlr_fifo_v1_state),
+	.move_state = surface_synced_move_state,
+};
+
+static void commit_destroy(struct fifo_commit *commit) {
+	wl_list_remove(&commit->link);
+	wlr_surface_unlock_cached(commit->fifo->surface, commit->seq);
+	free(commit);
+}
+
+static void fifo_signal_barrier(struct wlr_fifo_v1 *fifo) {
+	// dequeue and unlock commits until we find one with a .set_barrier request,
+	// in which case leave the barrier condition set.
+	struct fifo_commit *commit, *tmp;
+	bool barrier_pending = false;
+	wl_list_for_each_safe(commit, tmp, &fifo->commits, link) {
+		barrier_pending = commit->barrier_pending;
+		commit_destroy(commit);
+		if (barrier_pending) {
+			break;
+		}
+	}
+
+	if (!barrier_pending) {
+		fifo->barrier_set = false;
+	}
+}
+
+static void fifo_reset(struct wlr_fifo_v1 *fifo) {
+	struct fifo_commit *commit, *tmp_co;
+	wl_list_for_each_safe(commit, tmp_co, &fifo->commits, link) {
+		commit_destroy(commit);
+	}
+	if (fifo->output) {
+		fifo->output_present.notify = NULL;
+		wl_list_remove(&fifo->output_present.link);
+		fifo->output_destroy.notify = NULL;
+		wl_list_remove(&fifo->output_destroy.link);
+	}
+	fifo->output = NULL;
+	fifo->pending = (struct wlr_fifo_v1_state){0};
+	fifo->current = (struct wlr_fifo_v1_state){0};
+	fifo->barrier_set = false;
+	fifo->surface_occluded_source_armed = false;
+	wl_event_source_timer_update(fifo->surface_occluded_source, 0);
+	fifo->last_output_present_nsec = 0;
+}
+
+static void fifo_handle_output_destroy(struct wl_listener *listener, void *data) {
+	struct wlr_fifo_v1 *fifo =
+		wl_container_of(listener, fifo, output_destroy);
+	fifo_reset(fifo);
+}
+
+static int handle_timer(void *data) {
+	struct wlr_fifo_v1 *fifo = data;
+	if (fifo->barrier_set) {
+		fifo_signal_barrier(fifo);
+	}
+	wl_event_source_timer_update(fifo->surface_occluded_source, 25);
+	return 0;
+}
+
+static void fifo_handle_output_present(struct wl_listener *listener, void *data) {
+	struct wlr_fifo_v1 *fifo =
+		wl_container_of(listener, fifo, output_present);
+	struct wlr_output_event_present *event = data;
+
+	if (fifo->surface_occluded_source_armed) {
+		return;
+	}
+
+	// We use the output.present event to advance the queue.
+	if (fifo->barrier_set) {
+		fifo_signal_barrier(fifo);
+	}
+	fifo->last_output_present_nsec = timespec_to_nsec(&event->when);
+}
+
+static void fifo_handle_commit(struct wl_listener *listener, void *data) {
+	struct wlr_fifo_v1 *fifo =
+		wl_container_of(listener, fifo, surface_commit);
+	if (fifo->current.set_barrier) {
+		fifo->barrier_set = true;
+	}
+}
+
+static bool should_queue_commit(struct wlr_fifo_v1 *fifo) {
+	return fifo->pending.wait_barrier && fifo->barrier_set;
+}
+
+static void fifo_handle_client_commit(struct wl_listener *listener, void *data) {
+	struct wlr_fifo_v1 *fifo =
+		wl_container_of(listener, fifo, surface_client_commit);
+
+	if (!fifo->surface || !should_queue_commit(fifo)) {
+		return;
+	}
+
+	struct fifo_commit *commit = calloc(1, sizeof(*commit));
+	if (!commit) {
+		wl_client_post_no_memory(wl_resource_get_client(fifo->resource));
+		return;
+	}
+	commit->fifo = fifo;
+
+	// If the commit, in addition to a .wait_barrier request, has a .set_barrier one,
+	// mark it so that we can set again the barrier when dequeing the commit.
+	if (fifo->pending.set_barrier) {
+		commit->barrier_pending = true;
+	}
+	commit->seq = wlr_surface_lock_pending(fifo->surface);
+	wl_list_insert(fifo->commits.prev, &commit->link);
+}
+
+static const struct wp_fifo_v1_interface fifo_implementation;
+static struct wlr_fifo_v1 *fifo_v1_from_resource(struct wl_resource *resource) {
+	assert(wl_resource_instance_of(resource, &wp_fifo_v1_interface,
+		&fifo_implementation));
+	return wl_resource_get_user_data(resource);
+}
+
+static void fifo_handle_wait_barrier(struct wl_client *client,
+		struct wl_resource *resource) {
+	struct wlr_fifo_v1 *fifo =
+		fifo_v1_from_resource(resource);
+	if (!fifo->surface) {
+		wl_resource_post_error(resource,
+			WP_FIFO_V1_ERROR_SURFACE_DESTROYED,
+			"the associated surface no longer exists");
+		return;
+	}
+	fifo->pending.wait_barrier = true;
+}
+
+static void fifo_handle_set_barrier(struct wl_client *client,
+		struct wl_resource *resource) {
+	struct wlr_fifo_v1 *fifo =
+		fifo_v1_from_resource(resource);
+	if (!fifo->surface) {
+		wl_resource_post_error(resource,
+			WP_FIFO_V1_ERROR_SURFACE_DESTROYED,
+			"the associated surface no longer exists");
+		return;
+	}
+	fifo->pending.set_barrier = true;
+}
+
+static void fifo_handle_resource_destroy(struct wl_resource *resource) {
+	struct wlr_fifo_v1 *fifo = fifo_v1_from_resource(resource);
+	wlr_surface_synced_finish(&fifo->synced);
+	wl_signal_emit_mutable(&fifo->events.destroy, NULL);
+	fifo_reset(fifo);
+	wl_event_source_remove(fifo->surface_occluded_source);
+	wlr_addon_finish(&fifo->addon);
+	wl_list_remove(&fifo->surface_client_commit.link);
+	wl_list_remove(&fifo->surface_commit.link);
+	free(fifo);
+}
+
+static void fifo_handle_destroy(struct wl_client *client,
+		struct wl_resource *resource) {
+	wl_resource_destroy(resource);
+}
+
+static void fifo_destroy(struct wlr_fifo_v1 *fifo) {
+	if (!fifo) {
+		return;
+	}
+	struct wl_resource *fifo_resource = fifo->resource;
+	fifo_handle_resource_destroy(fifo->resource);
+	wl_resource_set_user_data(fifo_resource, NULL);
+}
+
+static void surface_fifo_addon_handle_destroy(struct wlr_addon *addon) {
+	struct wlr_fifo_v1 *fifo = wl_container_of(addon, fifo, addon);
+	fifo_destroy(fifo);
+}
+
+static const struct wlr_addon_interface surface_fifo_addon_impl = {
+	.name = "wp_fifo_v1",
+	.destroy = surface_fifo_addon_handle_destroy,
+};
+
+static const struct wp_fifo_v1_interface fifo_implementation = {
+	.destroy = fifo_handle_destroy,
+	.set_barrier = fifo_handle_set_barrier,
+	.wait_barrier = fifo_handle_wait_barrier
+};
+
+static const struct wp_fifo_manager_v1_interface fifo_manager_impl;
+static struct wlr_fifo_manager_v1 *fifo_manager_v1_from_resource(struct wl_resource *resource) {
+	assert(wl_resource_instance_of(resource, &wp_fifo_manager_v1_interface,
+		&fifo_manager_impl));
+	return wl_resource_get_user_data(resource);
+}
+
+static void fifo_manager_handle_get_fifo(struct wl_client *wl_client, struct wl_resource *manager_resource,
+		uint32_t id, struct wl_resource *surface_resource) {
+	struct wlr_surface *surface = wlr_surface_from_resource(surface_resource);
+	if (wlr_addon_find(&surface->addons, NULL, &surface_fifo_addon_impl) != NULL) {
+		wl_resource_post_error(manager_resource,
+			WP_FIFO_MANAGER_V1_ERROR_ALREADY_EXISTS,
+			"A wp_fifo_v1 object already exists for this surface");
+		return;
+	}
+
+	struct wlr_fifo_v1 *fifo = calloc(1, sizeof(*fifo));
+	if (!fifo) {
+		wl_client_post_no_memory(wl_client);
+		return;
+	}
+	fifo->surface = surface;
+	struct wlr_fifo_manager_v1 *fifo_manager =
+		fifo_manager_v1_from_resource(manager_resource);
+	fifo->manager = fifo_manager;
+	fifo_manager->display = wl_client_get_display(wl_client);
+
+	if (!wlr_surface_synced_init(&fifo->synced, surface,
+			&surface_synced_impl, &fifo->pending, &fifo->current)) {
+		free(fifo);
+		wl_client_post_no_memory(wl_client);
+		return;
+	}
+
+	fifo->resource = wl_resource_create(wl_client, &wp_fifo_v1_interface,
+		wl_resource_get_version(manager_resource), id);
+	if (fifo->resource == NULL) {
+		wlr_surface_synced_finish(&fifo->synced);
+		free(fifo);
+		wl_client_post_no_memory(wl_client);
+		return;
+	}
+	wl_resource_set_implementation(fifo->resource, &fifo_implementation, fifo,
+		fifo_handle_resource_destroy);
+
+	wl_list_init(&fifo->commits);
+	wl_signal_init(&fifo->events.destroy);
+
+	fifo->surface_client_commit.notify = fifo_handle_client_commit;
+	wl_signal_add(&surface->events.client_commit, &fifo->surface_client_commit);
+	fifo->surface_commit.notify = fifo_handle_commit;
+	wl_signal_add(&surface->events.commit, &fifo->surface_commit);
+
+	wlr_addon_init(&fifo->addon, &surface->addons, NULL, &surface_fifo_addon_impl);
+
+	// If the surface is occluded, and there is no other surface updating the output's contents,
+	// then we won't receive any output events. For this case, we introduce a timer ticking at
+	// a heuristically defined value (40hz) so that we can advance the queue.
+	//
+	// The timer is armed only when the surface is occluded, and re-armed when it expires.
+	fifo->surface_occluded_source =
+		wl_event_loop_add_timer(wl_display_get_event_loop(fifo->manager->display),
+			handle_timer, fifo);
+	if (!fifo->surface_occluded_source) {
+		wl_client_post_no_memory(wl_client);
+		return;
+	}
+
+	wl_signal_emit_mutable(&fifo->manager->events.new_fifo,
+		&(struct wlr_fifo_manager_v1_new_fifo_event){.fifo = fifo});
+}
+
+static void fifo_manager_handle_destroy(struct wl_client *wl_client, struct wl_resource *resource) {
+	wl_resource_destroy(resource);
+}
+
+static const struct wp_fifo_manager_v1_interface fifo_manager_impl = {
+	.get_fifo = fifo_manager_handle_get_fifo,
+	.destroy = fifo_manager_handle_destroy,
+};
+
+static void fifo_manager_bind(struct wl_client *wl_client, void *data, uint32_t version,
+		uint32_t id) {
+	struct wlr_fifo_manager_v1 *fifo_manager = data;
+	struct wl_resource *resource =
+		wl_resource_create(wl_client, &wp_fifo_manager_v1_interface, version, id);
+	if (!resource) {
+		wl_client_post_no_memory(wl_client);
+		return;
+	}
+	wl_resource_set_implementation(resource, &fifo_manager_impl, fifo_manager, NULL);
+}
+
+static void fifo_manager_handle_display_destroy(struct wl_listener *listener, void *data) {
+	struct wlr_fifo_manager_v1 *fifo_manager =
+		wl_container_of(listener, fifo_manager, display_destroy);
+	wl_signal_emit_mutable(&fifo_manager->events.destroy, NULL);
+	wl_list_remove(&fifo_manager->display_destroy.link);
+	wl_global_destroy(fifo_manager->global);
+	free(fifo_manager);
+}
+
+struct wlr_fifo_manager_v1 *wlr_fifo_manager_v1_create(struct wl_display *display, uint32_t version) {
+	assert(version <= FIFO_MANAGER_VERSION);
+
+	struct wlr_fifo_manager_v1 *fifo_manager = calloc(1, sizeof(*fifo_manager));
+	if (!fifo_manager) {
+		return NULL;
+	}
+
+	fifo_manager->global = wl_global_create(display, &wp_fifo_manager_v1_interface,
+		version, fifo_manager, fifo_manager_bind);
+	if (!fifo_manager->global) {
+		free(fifo_manager);
+		return NULL;
+	}
+
+	wl_signal_init(&fifo_manager->events.destroy);
+	wl_signal_init(&fifo_manager->events.new_fifo);
+
+	fifo_manager->display_destroy.notify = fifo_manager_handle_display_destroy;
+	wl_display_add_destroy_listener(display, &fifo_manager->display_destroy);
+
+	return fifo_manager;
+}
+
+void wlr_fifo_v1_set_output(struct wlr_fifo_v1 *fifo, struct wlr_output *output) {
+	fifo_reset(fifo);
+
+	if (!output) {
+		// Here we arm the timer for the first time.
+		// When it expires, it might be re-armed at handle_timer().
+		if (!fifo->surface_occluded_source_armed) {
+			wl_event_source_timer_update(fifo->surface_occluded_source, 25);
+			fifo->surface_occluded_source_armed = true;
+		}
+		return;
+	}
+
+	fifo->output = output;
+	fifo->output_present.notify = fifo_handle_output_present;
+	wl_signal_add(&fifo->output->events.present, &fifo->output_present);
+	fifo->output_destroy.notify = fifo_handle_output_destroy;
+	wl_signal_add(&fifo->output->events.destroy, &fifo->output_destroy);
+}
diff --git a/util/time.c b/util/time.c
index 1a8f3296..7db0893b 100644
--- a/util/time.c
+++ b/util/time.c
@@ -22,6 +22,12 @@ int64_t get_current_time_msec(void) {
 	return timespec_to_msec(&now);
 }
 
+int64_t get_current_time_nsec(void) {
+	struct timespec now;
+	clock_gettime(CLOCK_MONOTONIC, &now);
+	return timespec_to_nsec(&now);
+}
+
 void timespec_sub(struct timespec *r, const struct timespec *a,
 		const struct timespec *b) {
 	r->tv_sec = a->tv_sec - b->tv_sec;