Merge pull request #160 from acrisci/feature/subcompositor

Subcompositor

8 files changed, 709 insertions, 167 deletions

diff --git a/include/rootston/desktop.h b/include/rootston/desktop.h
index 392b0271..91ac87b7 100644
--- a/include/rootston/desktop.h
+++ b/include/rootston/desktop.h
@@ -52,7 +52,8 @@ struct roots_desktop *desktop_create(struct roots_server *server,
 void desktop_destroy(struct roots_desktop *desktop);
 
 void view_destroy(struct roots_view *view);
-struct roots_view *view_at(struct roots_desktop *desktop, int x, int y);
+struct roots_view *view_at(struct roots_desktop *desktop, double lx, double ly,
+		struct wlr_surface **surface, double *sx, double *sy);
 void view_activate(struct roots_view *view, bool activate);
 
 void output_add_notify(struct wl_listener *listener, void *data);
diff --git a/include/wlr/types/wlr_surface.h b/include/wlr/types/wlr_surface.h
index 87d421e3..ae278815 100644
--- a/include/wlr/types/wlr_surface.h
+++ b/include/wlr/types/wlr_surface.h
@@ -18,6 +18,8 @@ struct wlr_frame_callback {
 #define WLR_SURFACE_INVALID_INPUT_REGION 16
 #define WLR_SURFACE_INVALID_TRANSFORM 32
 #define WLR_SURFACE_INVALID_SCALE 64
+#define WLR_SURFACE_INVALID_SUBSURFACE_POSITION 128
+#define WLR_SURFACE_INVALID_FRAME_CALLBACK_LIST 256
 
 struct wlr_surface_state {
 	uint32_t invalid;
@@ -29,13 +31,36 @@ struct wlr_surface_state {
 	int32_t scale;
 	int width, height;
 	int buffer_width, buffer_height;
+
+	struct {
+		int32_t x, y;
+	} subsurface_position;
+
+	struct wl_list frame_callback_list; // wl_surface.frame
+};
+
+struct wlr_subsurface {
+	struct wl_resource *resource;
+	struct wlr_surface *surface;
+	struct wlr_surface *parent;
+
+	struct wlr_surface_state *cached;
+	bool has_cache;
+
+	bool synchronized;
+	bool reordered;
+
+	struct wl_list parent_link;
+	struct wl_list parent_pending_link;
+
+	struct wl_listener parent_destroy_listener;
 };
 
 struct wlr_surface {
 	struct wl_resource *resource;
 	struct wlr_renderer *renderer;
 	struct wlr_texture *texture;
-	struct wlr_surface_state current, pending;
+	struct wlr_surface_state *current, *pending;
 	const char *role; // the lifetime-bound role or null
 
 	float buffer_to_surface_matrix[16];
@@ -47,11 +72,16 @@ struct wlr_surface {
 		struct wl_signal destroy;
 	} signals;
 
-	struct wl_list frame_callback_list; // wl_surface.frame
-
-	struct wl_listener compositor_listener; // destroy listener used by compositor
+	// destroy listener used by compositor
+	struct wl_listener compositor_listener;
 	void *compositor_data;
 
+	// subsurface properties
+	struct wlr_subsurface *subsurface;
+	struct wl_list subsurface_list; // wlr_subsurface::parent_link
+
+	// wlr_subsurface::parent_pending_link
+	struct wl_list subsurface_pending_list;
 	void *data;
 };
 
@@ -80,4 +110,15 @@ void wlr_surface_get_matrix(struct wlr_surface *surface,
 int wlr_surface_set_role(struct wlr_surface *surface, const char *role,
 		struct wl_resource *error_resource, uint32_t error_code);
 
+/**
+ * Create the subsurface implementation for this surface.
+ */
+void wlr_surface_make_subsurface(struct wlr_surface *surface,
+		struct wlr_surface *parent, uint32_t id);
+
+/**
+ * Get the top of the subsurface tree for this surface.
+ */
+struct wlr_surface *wlr_surface_get_main_surface(struct wlr_surface *surface);
+
 #endif
diff --git a/rootston/cursor.c b/rootston/cursor.c
index bd8f91d2..c24e6989 100644
--- a/rootston/cursor.c
+++ b/rootston/cursor.c
@@ -48,15 +48,14 @@ void view_begin_resize(struct roots_input *input, struct wlr_cursor *cursor,
 void cursor_update_position(struct roots_input *input, uint32_t time) {
 	struct roots_desktop *desktop = input->server->desktop;
 	struct roots_view *view;
+	struct wlr_surface *surface;
+	double sx, sy;
 	switch (input->mode) {
 	case ROOTS_CURSOR_PASSTHROUGH:
-		view = view_at(desktop, input->cursor->x, input->cursor->y);
+		view = view_at(desktop, input->cursor->x, input->cursor->y, &surface,
+			&sx, &sy);
 		if (view) {
-			struct wlr_box box;
-			view_get_input_bounds(view, &box);
-			double sx = input->cursor->x - view->x;
-			double sy = input->cursor->y - view->y;
-			wlr_seat_pointer_enter(input->wl_seat, view->wlr_surface, sx, sy);
+			wlr_seat_pointer_enter(input->wl_seat, surface, sx, sy);
 			wlr_seat_pointer_send_motion(input->wl_seat, time, sx, sy);
 		} else {
 			wlr_seat_pointer_clear_focus(input->wl_seat);
@@ -146,8 +145,10 @@ static void do_cursor_button_press(struct roots_input *input,
 		struct wlr_cursor *cursor, struct wlr_input_device *device,
 		uint32_t time, uint32_t button, uint32_t state) {
 	struct roots_desktop *desktop = input->server->desktop;
+	struct wlr_surface *surface;
+	double sx, sy;
 	struct roots_view *view = view_at(desktop,
-			input->cursor->x, input->cursor->y);
+			input->cursor->x, input->cursor->y, &surface, &sx, &sy);
 	uint32_t serial = wlr_seat_pointer_send_button(
 			input->wl_seat, time, button, state);
 	int i;
@@ -165,7 +166,7 @@ static void do_cursor_button_press(struct roots_input *input,
 			% (sizeof(input->input_events) / sizeof(input->input_events[0]));
 		set_view_focus(input, desktop, view);
 		if (view) {
-			wlr_seat_keyboard_enter(input->wl_seat, view->wlr_surface);
+			wlr_seat_keyboard_enter(input->wl_seat, surface);
 		}
 		break;
 	}
diff --git a/rootston/desktop.c b/rootston/desktop.c
index 3d307ee4..fcfc0ccf 100644
--- a/rootston/desktop.c
+++ b/rootston/desktop.c
@@ -31,8 +31,8 @@ void view_get_size(struct roots_view *view, struct wlr_box *box) {
 		return;
 	}
 	box->x = box->y = 0;
-	box->width = view->wlr_surface->current.width;
-	box->height = view->wlr_surface->current.height;
+	box->width = view->wlr_surface->current->width;
+	box->height = view->wlr_surface->current->height;
 }
 
 void view_get_input_bounds(struct roots_view *view, struct wlr_box *box) {
@@ -41,8 +41,8 @@ void view_get_input_bounds(struct roots_view *view, struct wlr_box *box) {
 		return;
 	}
 	box->x = box->y = 0;
-	box->width = view->wlr_surface->current.width;
-	box->height = view->wlr_surface->current.height;
+	box->width = view->wlr_surface->current->width;
+	box->height = view->wlr_surface->current->height;
 }
 
 void view_activate(struct roots_view *view, bool activate) {
@@ -57,14 +57,60 @@ void view_resize(struct roots_view *view, uint32_t width, uint32_t height) {
 	}
 }
 
-struct roots_view *view_at(struct roots_desktop *desktop, int x, int y) {
+static struct wlr_subsurface *subsurface_at(struct wlr_surface *surface,
+		double sx, double sy, double *sub_x, double *sub_y) {
+	struct wlr_subsurface *subsurface;
+	wl_list_for_each(subsurface, &surface->subsurface_list, parent_link) {
+		double _sub_x = subsurface->surface->current->subsurface_position.x;
+		double _sub_y = subsurface->surface->current->subsurface_position.y;
+		struct wlr_subsurface *sub =
+			subsurface_at(subsurface->surface, _sub_x + sx, _sub_y + sy,
+				sub_x, sub_y);
+		if (sub) {
+			// TODO: convert sub_x and sub_y to the parent coordinate system
+			return sub;
+		}
+
+		int sub_width = subsurface->surface->current->buffer_width;
+		int sub_height = subsurface->surface->current->buffer_height;
+		if ((sx > _sub_x && sx < _sub_x + sub_width) &&
+				(sy > _sub_y && sub_y < sub_y + sub_height)) {
+			*sub_x = _sub_x;
+			*sub_y = _sub_y;
+			return subsurface;
+		}
+	}
+
+	return NULL;
+}
+
+struct roots_view *view_at(struct roots_desktop *desktop, double lx, double ly,
+		struct wlr_surface **surface, double *sx, double *sy) {
 	for (size_t i = 0; i < desktop->views->length; ++i) {
 		struct roots_view *view = desktop->views->items[i];
+
+		double view_sx = lx - view->x;
+		double view_sy = ly - view->y;
+
+		double sub_x, sub_y;
+		struct wlr_subsurface *subsurface =
+			subsurface_at(view->wlr_surface, view_sx, view_sy, &sub_x, &sub_y);
+
+		if (subsurface) {
+			*sx = view_sx - sub_x;
+			*sy = view_sy - sub_y;
+			*surface = subsurface->surface;
+			return view;
+		}
+
 		struct wlr_box box;
 		view_get_input_bounds(view, &box);
 		box.x += view->x;
 		box.y += view->y;
-		if (wlr_box_contains_point(&box, x, y)) {
+		if (wlr_box_contains_point(&box, lx, ly)) {
+			*sx = view_sx;
+			*sy = view_sy;
+			*surface = view->wlr_surface;
 			return view;
 		}
 	}
diff --git a/rootston/output.c b/rootston/output.c
index 5aeb71b1..14d1783e 100644
--- a/rootston/output.c
+++ b/rootston/output.c
@@ -16,28 +16,49 @@ static inline int64_t timespec_to_msec(const struct timespec *a) {
 	return (int64_t)a->tv_sec * 1000 + a->tv_nsec / 1000000;
 }
 
-static void render_view(struct roots_desktop *desktop,
-		struct wlr_output *wlr_output, struct timespec *when,
-		struct roots_view *view, double ox, double oy) {
-	struct wlr_surface *surface = view->wlr_surface;
-	float matrix[16];
-	float transform[16];
+static void render_surface(struct wlr_surface *surface,
+		struct roots_desktop *desktop, struct wlr_output *wlr_output,
+		struct timespec *when, double lx, double ly) {
 	wlr_surface_flush_damage(surface);
 	if (surface->texture->valid) {
-		wlr_matrix_translate(&transform, ox, oy, 0);
-		wlr_surface_get_matrix(surface, &matrix,
-			&wlr_output->transform_matrix, &transform);
-		wlr_render_with_matrix(desktop->server->renderer,
-				surface->texture, &matrix);
-
-		struct wlr_frame_callback *cb, *cnext;
-		wl_list_for_each_safe(cb, cnext, &surface->frame_callback_list, link) {
-			wl_callback_send_done(cb->resource, timespec_to_msec(when));
-			wl_resource_destroy(cb->resource);
+		int width = surface->current->buffer_width;
+		int height = surface->current->buffer_height;
+		double ox = lx, oy = ly;
+		wlr_output_layout_output_coords(desktop->layout, wlr_output, &ox, &oy);
+
+		if (wlr_output_layout_intersects(desktop->layout, wlr_output,
+					lx, ly, lx + width, ly + height)) {
+			float matrix[16];
+			float transform[16];
+			wlr_matrix_translate(&transform, ox, oy, 0);
+			wlr_surface_get_matrix(surface, &matrix,
+					&wlr_output->transform_matrix, &transform);
+			wlr_render_with_matrix(desktop->server->renderer,
+					surface->texture, &matrix);
+
+			struct wlr_frame_callback *cb, *cnext;
+			wl_list_for_each_safe(cb, cnext,
+				&surface->current->frame_callback_list, link) {
+				wl_callback_send_done(cb->resource, timespec_to_msec(when));
+				wl_resource_destroy(cb->resource);
+			}
+		}
+
+		struct wlr_subsurface *subsurface;
+		wl_list_for_each(subsurface, &surface->subsurface_list, parent_link) {
+			render_surface(subsurface->surface, desktop, wlr_output, when,
+				lx + subsurface->surface->current->subsurface_position.x,
+				ly + subsurface->surface->current->subsurface_position.y);
 		}
 	}
 }
 
+static void render_view(struct roots_view *view, struct roots_desktop *desktop,
+		struct wlr_output *wlr_output, struct timespec *when) {
+	render_surface(view->wlr_surface, desktop, wlr_output, when,
+		view->x, view->y);
+}
+
 static void output_frame_notify(struct wl_listener *listener, void *data) {
 	struct wlr_output *wlr_output = data;
 	struct roots_output *output = wl_container_of(listener, output, frame);
@@ -52,16 +73,7 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 
 	for (size_t i = 0; i < desktop->views->length; ++i) {
 		struct roots_view *view = desktop->views->items[i];
-		int width = view->wlr_surface->current.buffer_width;
-		int height = view->wlr_surface->current.buffer_height;
-
-		if (wlr_output_layout_intersects(desktop->layout, wlr_output,
-					view->x, view->y, view->x + width, view->y + height)) {
-			double ox = view->x, oy = view->y;
-			wlr_output_layout_output_coords(
-					desktop->layout, wlr_output, &ox, &oy);
-			render_view(desktop, wlr_output, &now, view, ox, oy);
-		}
+		render_view(view, desktop, wlr_output, &now);
 	}
 
 	wlr_renderer_end(server->renderer);
diff --git a/types/wlr_compositor.c b/types/wlr_compositor.c
index 0658f65e..12903cda 100644
--- a/types/wlr_compositor.c
+++ b/types/wlr_compositor.c
@@ -19,9 +19,11 @@ static void wl_compositor_create_surface(struct wl_client *client,
 			compositor->renderer);
 	surface->compositor_data = compositor;
 	surface->compositor_listener.notify = &destroy_surface_listener;
-	wl_resource_add_destroy_listener(surface_resource, &surface->compositor_listener);
+	wl_resource_add_destroy_listener(surface_resource,
+		&surface->compositor_listener);
 
-	wl_list_insert(&compositor->surfaces, wl_resource_get_link(surface_resource));
+	wl_list_insert(&compositor->surfaces,
+		wl_resource_get_link(surface_resource));
 	wl_signal_emit(&compositor->events.create_surface, surface);
 }
 
@@ -52,15 +54,17 @@ static void wl_compositor_bind(struct wl_client *wl_client, void *_compositor,
 	struct wlr_compositor *compositor = _compositor;
 	assert(wl_client && compositor);
 	if (version > 4) {
-		wlr_log(L_ERROR, "Client requested unsupported wl_compositor version, disconnecting");
+		wlr_log(L_ERROR, "Client requested unsupported wl_compositor version, "
+			"disconnecting");
 		wl_client_destroy(wl_client);
 		return;
 	}
-	struct wl_resource *wl_resource = wl_resource_create(
-			wl_client, &wl_compositor_interface, version, id);
+	struct wl_resource *wl_resource =
+		wl_resource_create(wl_client, &wl_compositor_interface, version, id);
 	wl_resource_set_implementation(wl_resource, &wl_compositor_impl,
-			compositor, wl_compositor_destroy);
-	wl_list_insert(&compositor->wl_resources, wl_resource_get_link(wl_resource));
+		compositor, wl_compositor_destroy);
+	wl_list_insert(&compositor->wl_resources,
+		wl_resource_get_link(wl_resource));
 }
 
 void wlr_compositor_destroy(struct wlr_compositor *compositor) {
@@ -68,19 +72,96 @@ void wlr_compositor_destroy(struct wlr_compositor *compositor) {
 	free(compositor);
 }
 
+static void subcompositor_destroy(struct wl_client *client,
+		struct wl_resource *resource) {
+	wl_resource_destroy(resource);
+}
+
+static void subcompositor_get_subsurface(struct wl_client *client,
+		struct wl_resource *resource, uint32_t id,
+		struct wl_resource *surface_resource,
+		struct wl_resource *parent_resource) {
+	struct wlr_surface *surface = wl_resource_get_user_data(surface_resource);
+	struct wlr_surface *parent = wl_resource_get_user_data(parent_resource);
+
+	static const char msg[] = "get_subsurface: wl_subsurface@";
+
+	if (surface == parent) {
+		wl_resource_post_error(resource,
+			WL_SUBCOMPOSITOR_ERROR_BAD_SURFACE,
+			"%s%d: wl_surface@%d cannot be its own parent",
+			msg, id, wl_resource_get_id(surface_resource));
+		return;
+	}
+
+	if (surface->subsurface) {
+		wl_resource_post_error(resource,
+			WL_SUBCOMPOSITOR_ERROR_BAD_SURFACE,
+			"%s%d: wl_surface@%d is already a sub-surface",
+			msg, id, wl_resource_get_id(surface_resource));
+		return;
+	}
+
+	if (wlr_surface_get_main_surface(parent) == surface) {
+		wl_resource_post_error(resource,
+			WL_SUBCOMPOSITOR_ERROR_BAD_SURFACE,
+			"%s%d: wl_surface@%d is an ancestor of parent",
+			msg, id, wl_resource_get_id(surface_resource));
+		return;
+	}
+
+	if (wlr_surface_set_role(surface, "wl_subsurface", resource,
+				WL_SUBCOMPOSITOR_ERROR_BAD_SURFACE) < 0) {
+		return;
+	}
+
+	wlr_surface_make_subsurface(surface, parent, id);
+	if (!surface->subsurface) {
+		wl_resource_post_no_memory(resource);
+		return;
+	}
+}
+
+
+static const struct wl_subcompositor_interface subcompositor_interface = {
+	.destroy = subcompositor_destroy,
+	.get_subsurface = subcompositor_get_subsurface,
+};
+
+static void subcompositor_bind(struct wl_client *client, void *data,
+		uint32_t version, uint32_t id) {
+	struct wlr_compositor *compositor = data;
+	struct wl_resource *resource =
+		wl_resource_create(client, &wl_subcompositor_interface, 1, id);
+	if (resource == NULL) {
+		wl_client_post_no_memory(client);
+		return;
+	}
+	wl_resource_set_implementation(resource, &subcompositor_interface,
+		compositor, NULL);
+}
+
 struct wlr_compositor *wlr_compositor_create(struct wl_display *display,
 		struct wlr_renderer *renderer) {
-	struct wlr_compositor *compositor = calloc(1, sizeof(struct wlr_compositor));
+	struct wlr_compositor *compositor =
+		calloc(1, sizeof(struct wlr_compositor));
 	if (!compositor) {
 		wlr_log_errno(L_ERROR, "Could not allocate wlr compositor");
 		return NULL;
 	}
-	struct wl_global *wl_global = wl_global_create(display,
+
+	struct wl_global *compositor_global = wl_global_create(display,
 		&wl_compositor_interface, 4, compositor, wl_compositor_bind);
-	compositor->wl_global = wl_global;
+
+	compositor->wl_global = compositor_global;
 	compositor->renderer = renderer;
+
+	wl_global_create(display, &wl_subcompositor_interface, 1, compositor,
+		subcompositor_bind);
+
 	wl_list_init(&compositor->wl_resources);
 	wl_list_init(&compositor->surfaces);
 	wl_signal_init(&compositor->events.create_surface);
+
 	return compositor;
 }
diff --git a/types/wlr_surface.c b/types/wlr_surface.c
index a9a54abe..e44ea9fc 100644
--- a/types/wlr_surface.c
+++ b/types/wlr_surface.c
@@ -7,7 +7,8 @@
 #include <wlr/types/wlr_surface.h>
 #include <wlr/render/matrix.h>
 
-static void surface_destroy(struct wl_client *client, struct wl_resource *resource) {
+static void surface_destroy(struct wl_client *client,
+		struct wl_resource *resource) {
 	wl_resource_destroy(resource);
 }
 
@@ -15,8 +16,9 @@ static void surface_attach(struct wl_client *client,
 		struct wl_resource *resource,
 		struct wl_resource *buffer, int32_t sx, int32_t sy) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	surface->pending.invalid |= WLR_SURFACE_INVALID_BUFFER;
-	surface->pending.buffer = buffer;
+
+	surface->pending->invalid |= WLR_SURFACE_INVALID_BUFFER;
+	surface->pending->buffer = buffer;
 }
 
 static void surface_damage(struct wl_client *client,
@@ -26,9 +28,9 @@ static void surface_damage(struct wl_client *client,
 	if (width < 0 || height < 0) {
 		return;
 	}
-	surface->pending.invalid |= WLR_SURFACE_INVALID_SURFACE_DAMAGE;
-	pixman_region32_union_rect(&surface->pending.surface_damage,
-		&surface->pending.surface_damage,
+	surface->pending->invalid |= WLR_SURFACE_INVALID_SURFACE_DAMAGE;
+	pixman_region32_union_rect(&surface->pending->surface_damage,
+		&surface->pending->surface_damage,
 		x, y, width, height);
 }
 
@@ -60,22 +62,24 @@ static void surface_frame(struct wl_client *client,
 	wl_resource_set_implementation(cb->resource,
 		NULL, cb, destroy_frame_callback);
 
-	wl_list_insert(surface->frame_callback_list.prev, &cb->link);
+	wl_list_insert(surface->pending->frame_callback_list.prev, &cb->link);
+
+	surface->pending->invalid |= WLR_SURFACE_INVALID_FRAME_CALLBACK_LIST;
 }
 
 static void surface_set_opaque_region(struct wl_client *client,
 		struct wl_resource *resource,
 		struct wl_resource *region_resource) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_OPAQUE_REGION)) {
-		pixman_region32_clear(&surface->pending.opaque);
+	if ((surface->pending->invalid & WLR_SURFACE_INVALID_OPAQUE_REGION)) {
+		pixman_region32_clear(&surface->pending->opaque);
 	}
-	surface->pending.invalid |= WLR_SURFACE_INVALID_OPAQUE_REGION;
+	surface->pending->invalid |= WLR_SURFACE_INVALID_OPAQUE_REGION;
 	if (region_resource) {
 		pixman_region32_t *region = wl_resource_get_user_data(region_resource);
-		pixman_region32_copy(&surface->pending.opaque, region);
+		pixman_region32_copy(&surface->pending->opaque, region);
 	} else {
-		pixman_region32_clear(&surface->pending.opaque);
+		pixman_region32_clear(&surface->pending->opaque);
 	}
 }
 
@@ -83,28 +87,28 @@ static void surface_set_input_region(struct wl_client *client,
 		struct wl_resource *resource,
 		struct wl_resource *region_resource) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_INPUT_REGION)) {
-		pixman_region32_clear(&surface->pending.input);
+	if ((surface->pending->invalid & WLR_SURFACE_INVALID_INPUT_REGION)) {
+		pixman_region32_clear(&surface->pending->input);
 	}
-	surface->pending.invalid |= WLR_SURFACE_INVALID_INPUT_REGION;
+	surface->pending->invalid |= WLR_SURFACE_INVALID_INPUT_REGION;
 	if (region_resource) {
 		pixman_region32_t *region = wl_resource_get_user_data(region_resource);
-		pixman_region32_copy(&surface->pending.input, region);
+		pixman_region32_copy(&surface->pending->input, region);
 	} else {
-		pixman_region32_init_rect(&surface->pending.input,
+		pixman_region32_init_rect(&surface->pending->input,
 			INT32_MIN, INT32_MIN, UINT32_MAX, UINT32_MAX);
 	}
 }
 
-static void wlr_surface_update_size(struct wlr_surface *surface) {
-	int scale = surface->current.scale;
-	enum wl_output_transform transform = surface->current.transform;
+static void wlr_surface_update_size(struct wlr_surface *surface, struct wlr_surface_state *state) {
+	int scale = state->scale;
+	enum wl_output_transform transform = state->transform;
 
-	wlr_texture_get_buffer_size(surface->texture, surface->current.buffer,
-		&surface->current.buffer_width, &surface->current.buffer_height);
+	wlr_texture_get_buffer_size(surface->texture, state->buffer,
+		&state->buffer_width, &state->buffer_height);
 
-	int _width = surface->current.buffer_width / scale;
-	int _height = surface->current.buffer_height / scale;
+	int _width = state->buffer_width / scale;
+	int _height = state->buffer_height / scale;
 
 	if (transform == WL_OUTPUT_TRANSFORM_90 ||
 		transform == WL_OUTPUT_TRANSFORM_270 ||
@@ -115,17 +119,18 @@ static void wlr_surface_update_size(struct wlr_surface *surface) {
 		_height = tmp;
 	}
 
-	surface->current.width = _width;
-	surface->current.height = _height;
+	wl_list_init(&state->frame_callback_list);
+
+	state->width = _width;
+	state->height = _height;
 }
 
-static void wlr_surface_to_buffer_region(struct wlr_surface *surface,
-		pixman_region32_t *surface_region, pixman_region32_t *buffer_region,
+static void wlr_surface_to_buffer_region(int scale,
+		enum wl_output_transform transform, pixman_region32_t *surface_region,
+		pixman_region32_t *buffer_region,
 		int width, int height) {
 	pixman_box32_t *src_rects, *dest_rects;
 	int nrects, i;
-	int scale = surface->current.scale;
-	enum wl_output_transform transform = surface->current.transform;
 
 	src_rects = pixman_region32_rectangles(surface_region, &nrects);
 	dest_rects = malloc(nrects * sizeof(*dest_rects));
@@ -201,89 +206,227 @@ static void wlr_surface_to_buffer_region(struct wlr_surface *surface,
 	free(dest_rects);
 }
 
-static void surface_commit(struct wl_client *client,
-		struct wl_resource *resource) {
-	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	bool update_size = false;
+/**
+ * Append pending state to current state and clear pending state.
+ */
+static void wlr_surface_move_state(struct wlr_surface *surface, struct wlr_surface_state *next,
+		struct wlr_surface_state *state) {
 	bool update_damage = false;
+	bool update_size = false;
 
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_SCALE)) {
-		surface->current.scale = surface->pending.scale;
+	if ((next->invalid & WLR_SURFACE_INVALID_SCALE)) {
+		state->scale = next->scale;
 		update_size = true;
 	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_TRANSFORM)) {
-		surface->current.transform = surface->pending.transform;
+	if ((next->invalid & WLR_SURFACE_INVALID_TRANSFORM)) {
+		state->transform = next->transform;
 		update_size = true;
 	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_BUFFER)) {
-		surface->current.buffer = surface->pending.buffer;
+	if ((next->invalid & WLR_SURFACE_INVALID_BUFFER)) {
+		if (state->buffer) {
+			wl_resource_post_event(state->buffer, WL_BUFFER_RELEASE);
+		}
+
+		state->buffer = next->buffer;
+		next->buffer = NULL;
 		update_size = true;
 	}
 	if (update_size) {
-		int32_t oldw = surface->current.buffer_width;
-		int32_t oldh = surface->current.buffer_height;
-		wlr_surface_update_size(surface);
-
-		surface->reupload_buffer = oldw != surface->current.buffer_width ||
-			oldh != surface->current.buffer_height;
-	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_SURFACE_DAMAGE)) {
-		pixman_region32_union(&surface->current.surface_damage,
-			&surface->current.surface_damage,
-			&surface->pending.surface_damage);
-		pixman_region32_intersect_rect(&surface->current.surface_damage,
-			&surface->current.surface_damage, 0, 0, surface->current.width,
-			surface->current.height);
-
-		pixman_region32_clear(&surface->pending.surface_damage);
+		wlr_surface_update_size(surface, state);
+	}
+	if ((next->invalid & WLR_SURFACE_INVALID_SURFACE_DAMAGE)) {
+		pixman_region32_union(&state->surface_damage,
+			&state->surface_damage,
+			&next->surface_damage);
+		pixman_region32_intersect_rect(&state->surface_damage,
+			&state->surface_damage, 0, 0, state->width,
+			state->height);
+
+		pixman_region32_clear(&next->surface_damage);
 		update_damage = true;
 	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_BUFFER_DAMAGE)) {
-		pixman_region32_union(&surface->current.buffer_damage,
-			&surface->current.buffer_damage,
-			&surface->pending.buffer_damage);
+	if ((next->invalid & WLR_SURFACE_INVALID_BUFFER_DAMAGE)) {
+		pixman_region32_union(&state->buffer_damage,
+			&state->buffer_damage,
+			&next->buffer_damage);
 
-		pixman_region32_clear(&surface->pending.buffer_damage);
+		pixman_region32_clear(&next->buffer_damage);
 		update_damage = true;
 	}
 	if (update_damage) {
 		pixman_region32_t buffer_damage;
 		pixman_region32_init(&buffer_damage);
-		wlr_surface_to_buffer_region(surface, &surface->current.surface_damage,
-			&buffer_damage, surface->current.width, surface->current.height);
-		pixman_region32_union(&surface->current.buffer_damage,
-			&surface->current.buffer_damage, &buffer_damage);
+		wlr_surface_to_buffer_region(state->scale, state->transform,
+			&state->surface_damage, &buffer_damage, state->width,
+			state->height);
+		pixman_region32_union(&state->buffer_damage,
+			&state->buffer_damage, &buffer_damage);
 		pixman_region32_fini(&buffer_damage);
 
-		pixman_region32_intersect_rect(&surface->current.buffer_damage,
-			&surface->current.buffer_damage, 0, 0,
-			surface->current.buffer_width, surface->current.buffer_height);
+		pixman_region32_intersect_rect(&state->buffer_damage,
+			&state->buffer_damage, 0, 0,
+			state->buffer_width, state->buffer_height);
 	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_OPAQUE_REGION)) {
+	if ((next->invalid & WLR_SURFACE_INVALID_OPAQUE_REGION)) {
 		// TODO: process buffer
-		pixman_region32_clear(&surface->pending.opaque);
+		pixman_region32_clear(&next->opaque);
 	}
-	if ((surface->pending.invalid & WLR_SURFACE_INVALID_INPUT_REGION)) {
+	if ((next->invalid & WLR_SURFACE_INVALID_INPUT_REGION)) {
 		// TODO: process buffer
-		pixman_region32_clear(&surface->pending.input);
+		pixman_region32_clear(&next->input);
+	}
+	if ((next->invalid & WLR_SURFACE_INVALID_SUBSURFACE_POSITION)) {
+		state->subsurface_position.x = next->subsurface_position.x;
+		state->subsurface_position.y = next->subsurface_position.y;
+		next->subsurface_position.x = 0;
+		next->subsurface_position.y = 0;
+	}
+	if ((next->invalid & WLR_SURFACE_INVALID_FRAME_CALLBACK_LIST)) {
+		wl_list_insert_list(&state->frame_callback_list, &next->frame_callback_list);
+		wl_list_init(&next->frame_callback_list);
+	}
+
+	state->invalid |= next->invalid;
+	next->invalid = 0;
+}
+
+static void wlr_surface_damage_subsurfaces(struct wlr_subsurface *subsurface) {
+	// XXX: This is probably the wrong way to do it, because this damage should
+	// come from the client, but weston doesn't do it correctly either and it
+	// seems to work ok. See the comment on weston_surface_damage for more info
+	// about a better approach.
+	struct wlr_surface *surface = subsurface->surface;
+	pixman_region32_union_rect(&surface->current->surface_damage,
+		&surface->current->surface_damage,
+		0, 0, surface->current->width,
+		surface->current->height);
+
+	subsurface->reordered = false;
+
+	struct wlr_subsurface *child;
+	wl_list_for_each(child, &subsurface->surface->subsurface_list, parent_link) {
+		wlr_surface_damage_subsurfaces(child);
+	}
+}
+
+static void wlr_surface_commit_pending(struct wlr_surface *surface) {
+	int32_t oldw = surface->current->buffer_width;
+	int32_t oldh = surface->current->buffer_height;
+
+	wlr_surface_move_state(surface, surface->pending, surface->current);
+
+	// commit subsurface order
+	struct wlr_subsurface *subsurface;
+	wl_list_for_each_reverse(subsurface, &surface->subsurface_pending_list,
+		parent_pending_link) {
+		wl_list_remove(&subsurface->parent_link);
+		wl_list_insert(&surface->subsurface_list, &subsurface->parent_link);
+
+		if (subsurface->reordered) {
+			// TODO: damage all the subsurfaces
+			wlr_surface_damage_subsurfaces(subsurface);
+		}
 	}
 
-	surface->pending.invalid = 0;
+	surface->reupload_buffer = oldw != surface->current->buffer_width ||
+		oldh != surface->current->buffer_height;
+
 	// TODO: add the invalid bitfield to this callback
 	wl_signal_emit(&surface->signals.commit, surface);
 }
 
+static bool wlr_subsurface_is_synchronized(struct wlr_subsurface *subsurface) {
+	while (subsurface) {
+		if (subsurface->synchronized) {
+			return true;
+		}
+
+		if (!subsurface->parent) {
+			return false;
+		}
+
+		subsurface = subsurface->parent->subsurface;
+	}
+
+	return false;
+}
+
+/**
+ * Recursive function to commit the effectively synchronized children.
+ */
+static void wlr_subsurface_parent_commit(struct wlr_subsurface *subsurface,
+		bool synchronized) {
+		struct wlr_surface *surface = subsurface->surface;
+	if (synchronized || subsurface->synchronized) {
+
+		if (subsurface->has_cache) {
+			wlr_surface_move_state(surface, subsurface->cached, surface->pending);
+			wlr_surface_commit_pending(surface);
+			subsurface->has_cache = false;
+			subsurface->cached->invalid = 0;
+		}
+
+		struct wlr_subsurface *tmp;
+		wl_list_for_each(tmp, &surface->subsurface_list, parent_link) {
+			wlr_subsurface_parent_commit(tmp, true);
+		}
+	}
+}
+
+static void wlr_subsurface_commit(struct wlr_subsurface *subsurface) {
+	struct wlr_surface *surface = subsurface->surface;
+
+	if (wlr_subsurface_is_synchronized(subsurface)) {
+		wlr_surface_move_state(surface, surface->pending, subsurface->cached);
+		subsurface->has_cache = true;
+	} else {
+		if (subsurface->has_cache) {
+			wlr_surface_move_state(surface, subsurface->cached, surface->pending);
+			wlr_surface_commit_pending(surface);
+			subsurface->has_cache = false;
+
+		} else {
+			wlr_surface_commit_pending(surface);
+		}
+
+		struct wlr_subsurface *tmp;
+		wl_list_for_each(tmp, &surface->subsurface_list, parent_link) {
+			wlr_subsurface_parent_commit(tmp, false);
+		}
+	}
+
+}
+
+static void surface_commit(struct wl_client *client,
+		struct wl_resource *resource) {
+	struct wlr_surface *surface = wl_resource_get_user_data(resource);
+	struct wlr_subsurface *subsurface = surface->subsurface;
+
+	if (subsurface) {
+		wlr_subsurface_commit(subsurface);
+		return;
+	}
+
+	wlr_surface_commit_pending(surface);
+
+	struct wlr_subsurface *tmp;
+	wl_list_for_each(tmp, &surface->subsurface_list, parent_link) {
+		wlr_subsurface_parent_commit(tmp, false);
+	}
+}
+
 void wlr_surface_flush_damage(struct wlr_surface *surface) {
-	if (!surface->current.buffer) {
+	if (!surface->current->buffer) {
 		if (surface->texture->valid) {
 			// TODO: Detach buffers
 		}
 		return;
 	}
-	struct wl_shm_buffer *buffer = wl_shm_buffer_get(surface->current.buffer);
+	struct wl_shm_buffer *buffer = wl_shm_buffer_get(surface->current->buffer);
 	if (!buffer) {
-		if (wlr_renderer_buffer_is_drm(surface->renderer, surface->pending.buffer)) {
-			wlr_texture_upload_drm(surface->texture, surface->pending.buffer);
+		if (wlr_renderer_buffer_is_drm(surface->renderer,
+					surface->current->buffer)) {
+			wlr_texture_upload_drm(surface->texture, surface->current->buffer);
 			goto release;
 		} else {
 			wlr_log(L_INFO, "Unknown buffer handle attached");
@@ -295,7 +438,7 @@ void wlr_surface_flush_damage(struct wlr_surface *surface) {
 	if (surface->reupload_buffer) {
 		wlr_texture_upload_shm(surface->texture, format, buffer);
 	} else {
-		pixman_region32_t damage = surface->current.buffer_damage;
+		pixman_region32_t damage = surface->current->buffer_damage;
 		if (!pixman_region32_not_empty(&damage)) {
 			goto release;
 		}
@@ -314,26 +457,26 @@ void wlr_surface_flush_damage(struct wlr_surface *surface) {
 	}
 
 release:
-	pixman_region32_clear(&surface->current.surface_damage);
-	pixman_region32_clear(&surface->current.buffer_damage);
+	pixman_region32_clear(&surface->current->surface_damage);
+	pixman_region32_clear(&surface->current->buffer_damage);
 
-	wl_resource_post_event(surface->current.buffer, WL_BUFFER_RELEASE);
-	surface->current.buffer = NULL;
+	wl_resource_post_event(surface->current->buffer, WL_BUFFER_RELEASE);
+	surface->current->buffer = NULL;
 }
 
 static void surface_set_buffer_transform(struct wl_client *client,
 		struct wl_resource *resource, int transform) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	surface->pending.invalid |= WLR_SURFACE_INVALID_TRANSFORM;
-	surface->pending.transform = transform;
+	surface->pending->invalid |= WLR_SURFACE_INVALID_TRANSFORM;
+	surface->pending->transform = transform;
 }
 
 static void surface_set_buffer_scale(struct wl_client *client,
 		struct wl_resource *resource,
 		int32_t scale) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
-	surface->pending.invalid |= WLR_SURFACE_INVALID_SCALE;
-	surface->pending.scale = scale;
+	surface->pending->invalid |= WLR_SURFACE_INVALID_SCALE;
+	surface->pending->scale = scale;
 }
 
 static void surface_damage_buffer(struct wl_client *client,
@@ -344,9 +487,9 @@ static void surface_damage_buffer(struct wl_client *client,
 	if (width < 0 || height < 0) {
 		return;
 	}
-	surface->pending.invalid |= WLR_SURFACE_INVALID_BUFFER_DAMAGE;
-	pixman_region32_union_rect(&surface->pending.buffer_damage,
-		&surface->pending.buffer_damage,
+	surface->pending->invalid |= WLR_SURFACE_INVALID_BUFFER_DAMAGE;
+	pixman_region32_union_rect(&surface->pending->buffer_damage,
+		&surface->pending->buffer_damage,
 		x, y, width, height);
 }
 
@@ -363,19 +506,62 @@ const struct wl_surface_interface surface_interface = {
 	.damage_buffer = surface_damage_buffer
 };
 
+static struct wlr_surface_state *wlr_surface_state_create() {
+	struct wlr_surface_state *state = calloc(1, sizeof(struct wlr_surface_state));
+	state->scale = 1;
+	state->transform = WL_OUTPUT_TRANSFORM_NORMAL;
+
+	wl_list_init(&state->frame_callback_list);
+
+	pixman_region32_init(&state->surface_damage);
+	pixman_region32_init(&state->buffer_damage);
+	pixman_region32_init(&state->opaque);
+	pixman_region32_init(&state->input);
+
+	return state;
+}
+
+static void wlr_surface_state_destroy(struct wlr_surface_state *state) {
+	struct wlr_frame_callback *cb, *tmp;
+	wl_list_for_each_safe(cb, tmp, &state->frame_callback_list, link) {
+		wl_resource_destroy(cb->resource);
+	}
+
+	pixman_region32_fini(&state->surface_damage);
+	pixman_region32_fini(&state->buffer_damage);
+	pixman_region32_fini(&state->opaque);
+	pixman_region32_fini(&state->input);
+
+	free(state);
+}
+
+void wlr_subsurface_destroy(struct wlr_subsurface *subsurface) {
+	wlr_surface_state_destroy(subsurface->cached);
+
+	if (subsurface->parent) {
+		wl_list_remove(&subsurface->parent_link);
+		wl_list_remove(&subsurface->parent_pending_link);
+		wl_list_remove(&subsurface->parent_destroy_listener.link);
+	}
+
+	wl_resource_set_user_data(subsurface->resource, NULL);
+	if (subsurface->surface) {
+		subsurface->surface->subsurface = NULL;
+	}
+	free(subsurface);
+}
+
 static void destroy_surface(struct wl_resource *resource) {
 	struct wlr_surface *surface = wl_resource_get_user_data(resource);
 	wl_signal_emit(&surface->signals.destroy, surface);
 
-	wlr_texture_destroy(surface->texture);
-	struct wlr_frame_callback *cb, *next;
-	wl_list_for_each_safe(cb, next, &surface->frame_callback_list, link) {
-		wl_resource_destroy(cb->resource);
+	if (surface->subsurface) {
+		wlr_subsurface_destroy(surface->subsurface);
 	}
-	pixman_region32_fini(&surface->pending.surface_damage);
-	pixman_region32_fini(&surface->pending.buffer_damage);
-	pixman_region32_fini(&surface->pending.opaque);
-	pixman_region32_fini(&surface->pending.input);
+
+	wlr_texture_destroy(surface->texture);
+	wlr_surface_state_destroy(surface->pending);
+	wlr_surface_state_destroy(surface->current);
 
 	free(surface);
 }
@@ -391,17 +577,14 @@ struct wlr_surface *wlr_surface_create(struct wl_resource *res,
 	surface->renderer = renderer;
 	surface->texture = wlr_render_texture_create(renderer);
 	surface->resource = res;
-	surface->current.scale = 1;
-	surface->pending.scale = 1;
-	surface->current.transform = WL_OUTPUT_TRANSFORM_NORMAL;
-	surface->pending.transform = WL_OUTPUT_TRANSFORM_NORMAL;
-	pixman_region32_init(&surface->pending.surface_damage);
-	pixman_region32_init(&surface->pending.buffer_damage);
-	pixman_region32_init(&surface->pending.opaque);
-	pixman_region32_init(&surface->pending.input);
+
+	surface->current = wlr_surface_state_create();
+	surface->pending = wlr_surface_state_create();
+
 	wl_signal_init(&surface->signals.commit);
 	wl_signal_init(&surface->signals.destroy);
-	wl_list_init(&surface->frame_callback_list);
+	wl_list_init(&surface->subsurface_list);
+	wl_list_init(&surface->subsurface_pending_list);
 	wl_resource_set_implementation(res, &surface_interface,
 		surface, destroy_surface);
 	return surface;
@@ -411,8 +594,8 @@ void wlr_surface_get_matrix(struct wlr_surface *surface,
 		float (*matrix)[16],
 		const float (*projection)[16],
 		const float (*transform)[16]) {
-	int width = surface->texture->width / surface->current.scale;
-	int height = surface->texture->height / surface->current.scale;
+	int width = surface->texture->width / surface->current->scale;
+	int height = surface->texture->height / surface->current->scale;
 	float scale[16];
 	wlr_matrix_identity(matrix);
 	if (transform) {
@@ -443,3 +626,180 @@ int wlr_surface_set_role(struct wlr_surface *surface, const char *role,
 
 	return -1;
 }
+
+static void subsurface_resource_destroy(struct wl_resource *resource) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+
+	if (subsurface) {
+		wlr_subsurface_destroy(subsurface);
+	}
+}
+
+static void subsurface_destroy(struct wl_client *client,
+		struct wl_resource *resource) {
+	wl_resource_destroy(resource);
+}
+
+static void subsurface_set_position(struct wl_client *client,
+		struct wl_resource *resource, int32_t x, int32_t y) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+	struct wlr_surface *surface = subsurface->surface;
+
+	surface->pending->invalid |= WLR_SURFACE_INVALID_SUBSURFACE_POSITION;
+
+	surface->pending->subsurface_position.x = x;
+	surface->pending->subsurface_position.y = y;
+}
+
+static struct wlr_subsurface *subsurface_find_sibling(
+		struct wlr_subsurface *subsurface, struct wlr_surface *surface) {
+	struct wlr_surface *parent = subsurface->parent;
+
+	struct wlr_subsurface *sibling;
+	wl_list_for_each(sibling, &parent->subsurface_list, parent_link) {
+		if (sibling->surface == surface && sibling != subsurface)
+			return sibling;
+	}
+
+	return NULL;
+}
+
+static void subsurface_place_above(struct wl_client *client,
+		struct wl_resource *resource, struct wl_resource *sibling_resource) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+
+	if (!subsurface) {
+		return;
+	}
+
+	struct wlr_surface *sibling_surface =
+		wl_resource_get_user_data(sibling_resource);
+	struct wlr_subsurface *sibling =
+		subsurface_find_sibling(subsurface, sibling_surface);
+
+	if (!sibling) {
+		wl_resource_post_error(subsurface->resource,
+			WL_SUBSURFACE_ERROR_BAD_SURFACE,
+			"%s: wl_surface@%d is not a parent or sibling",
+			"place_above", wl_resource_get_id(sibling_surface->resource));
+		return;
+	}
+
+	wl_list_remove(&subsurface->parent_pending_link);
+	wl_list_insert(sibling->parent_pending_link.prev,
+		&subsurface->parent_pending_link);
+
+	subsurface->reordered = true;
+}
+
+static void subsurface_place_below(struct wl_client *client,
+		struct wl_resource *resource, struct wl_resource *sibling_resource) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+
+	struct wlr_surface *sibling_surface =
+		wl_resource_get_user_data(sibling_resource);
+	struct wlr_subsurface *sibling =
+		subsurface_find_sibling(subsurface, sibling_surface);
+
+	if (!sibling) {
+		wl_resource_post_error(subsurface->resource,
+			WL_SUBSURFACE_ERROR_BAD_SURFACE,
+			"%s: wl_surface@%d is not a parent or sibling",
+			"place_below", wl_resource_get_id(sibling_surface->resource));
+		return;
+	}
+
+	wl_list_remove(&subsurface->parent_pending_link);
+	wl_list_insert(&sibling->parent_pending_link,
+		&subsurface->parent_pending_link);
+
+	subsurface->reordered = true;
+}
+
+static void subsurface_set_sync(struct wl_client *client,
+		struct wl_resource *resource) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+
+	if (subsurface) {
+		subsurface->synchronized = true;
+	}
+}
+
+static void subsurface_set_desync(struct wl_client *client,
+		struct wl_resource *resource) {
+	struct wlr_subsurface *subsurface = wl_resource_get_user_data(resource);
+
+	if (subsurface && subsurface->synchronized) {
+		subsurface->synchronized = false;
+
+		if (!wlr_subsurface_is_synchronized(subsurface)) {
+			// TODO: do a synchronized commit to flush the cache
+			wlr_subsurface_parent_commit(subsurface, true);
+		}
+	}
+}
+
+static const struct wl_subsurface_interface subsurface_implementation = {
+	.destroy = subsurface_destroy,
+	.set_position = subsurface_set_position,
+	.place_above = subsurface_place_above,
+	.place_below = subsurface_place_below,
+	.set_sync = subsurface_set_sync,
+	.set_desync = subsurface_set_desync,
+};
+
+static void subsurface_handle_parent_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_subsurface *subsurface =
+		wl_container_of(listener, subsurface, parent_destroy_listener);
+	wl_list_remove(&subsurface->parent_link);
+	wl_list_remove(&subsurface->parent_pending_link);
+	wl_list_remove(&subsurface->parent_destroy_listener.link);
+	subsurface->parent = NULL;
+}
+
+void wlr_surface_make_subsurface(struct wlr_surface *surface,
+		struct wlr_surface *parent, uint32_t id) {
+	assert(surface->subsurface == NULL);
+
+	struct wlr_subsurface *subsurface =
+		calloc(1, sizeof(struct wlr_subsurface));
+	if (!subsurface) {
+		return;
+	}
+	subsurface->cached = wlr_surface_state_create();
+	subsurface->synchronized = true;
+	subsurface->surface = surface;
+
+	// link parent
+	subsurface->parent = parent;
+	wl_signal_add(&parent->signals.destroy,
+		&subsurface->parent_destroy_listener);
+	subsurface->parent_destroy_listener.notify =
+		subsurface_handle_parent_destroy;
+	wl_list_insert(&parent->subsurface_list, &subsurface->parent_link);
+	wl_list_insert(&parent->subsurface_pending_list,
+		&subsurface->parent_pending_link);
+
+	struct wl_client *client = wl_resource_get_client(surface->resource);
+
+	subsurface->resource =
+		wl_resource_create(client, &wl_subsurface_interface, 1, id);
+
+	wl_resource_set_implementation(subsurface->resource,
+		&subsurface_implementation, subsurface,
+		subsurface_resource_destroy);
+
+	surface->subsurface = subsurface;
+}
+
+
+struct wlr_surface *wlr_surface_get_main_surface(struct wlr_surface *surface) {
+	struct wlr_subsurface *sub;
+
+	while (surface && (sub = surface->subsurface)) {
+		surface = sub->parent;
+	}
+
+	return surface;
+}
diff --git a/types/wlr_xdg_shell_v6.c b/types/wlr_xdg_shell_v6.c
index a7450add..9f623420 100644
--- a/types/wlr_xdg_shell_v6.c
+++ b/types/wlr_xdg_shell_v6.c
@@ -496,7 +496,7 @@ static void wlr_xdg_surface_v6_toplevel_committed(
 		struct wlr_xdg_surface_v6 *surface) {
 	assert(surface->role == WLR_XDG_SURFACE_V6_ROLE_TOPLEVEL);
 
-	if (!surface->surface->current.buffer && !surface->toplevel_state->added) {
+	if (!surface->surface->current->buffer && !surface->toplevel_state->added) {
 		// on the first commit, send a configure request to tell the client it
 		// is added
 		wlr_xdg_surface_v6_schedule_configure(surface, true);
@@ -504,7 +504,7 @@ static void wlr_xdg_surface_v6_toplevel_committed(
 		return;
 	}
 
-	if (!surface->surface->current.buffer) {
+	if (!surface->surface->current->buffer) {
 		return;
 	}
 
@@ -516,7 +516,7 @@ static void handle_wlr_surface_committed(struct wl_listener *listener,
 	struct wlr_xdg_surface_v6 *surface =
 		wl_container_of(listener, surface, surface_commit_listener);
 
-	if (surface->surface->current.buffer && !surface->configured) {
+	if (surface->surface->current->buffer && !surface->configured) {
 		wl_resource_post_error(surface->resource,
 			ZXDG_SURFACE_V6_ERROR_UNCONFIGURED_BUFFER,
 			"xdg_surface has never been configured");
@@ -580,7 +580,7 @@ static void xdg_shell_get_xdg_surface(struct wl_client *wl_client,
 		&zxdg_surface_v6_interface, wl_resource_get_version(client_resource),
 		id);
 
-	if (surface->surface->current.buffer != NULL) {
+	if (surface->surface->current->buffer != NULL) {
 		wl_resource_post_error(surface->resource,
 			ZXDG_SURFACE_V6_ERROR_UNCONFIGURED_BUFFER,
 			"xdg_surface must not have a buffer at creation");