Merge pull request #1517 from emersion/refactor-dnd

Refactor drag-and-drop

11 files changed, 355 insertions, 184 deletions

diff --git a/include/rootston/seat.h b/include/rootston/seat.h
index a91d8481..b91f9578 100644
--- a/include/rootston/seat.h
+++ b/include/rootston/seat.h
@@ -40,7 +40,8 @@ struct roots_seat {
 
 	struct wl_listener request_set_selection;
 	struct wl_listener request_set_primary_selection;
-	struct wl_listener new_drag_icon;
+	struct wl_listener request_start_drag;
+	struct wl_listener start_drag;
 	struct wl_listener destroy;
 };
 
diff --git a/include/types/wlr_data_device.h b/include/types/wlr_data_device.h
index 28073880..5865c999 100644
--- a/include/types/wlr_data_device.h
+++ b/include/types/wlr_data_device.h
@@ -30,9 +30,6 @@ void data_source_notify_finish(struct wlr_data_source *source);
 
 struct wlr_seat_client *seat_client_from_data_device_resource(
 	struct wl_resource *resource);
-bool seat_client_start_drag(struct wlr_seat_client *client,
-	struct wlr_data_source *source, struct wlr_surface *icon_surface,
-	struct wlr_surface *origin, uint32_t serial);
 /**
  * Creates a new wl_data_offer if there is a wl_data_source currently set as
  * the seat selection and sends it to the seat client, followed by the
diff --git a/include/wlr/types/wlr_data_device.h b/include/wlr/types/wlr_data_device.h
index 59aa718f..256654e5 100644
--- a/include/wlr/types/wlr_data_device.h
+++ b/include/wlr/types/wlr_data_device.h
@@ -89,15 +89,13 @@ struct wlr_data_source {
 	} events;
 };
 
+struct wlr_drag;
+
 struct wlr_drag_icon {
+	struct wlr_drag *drag;
 	struct wlr_surface *surface;
-	struct wlr_seat_client *client;
-	struct wl_list link; // wlr_seat::drag_icons
 	bool mapped;
 
-	bool is_pointer;
-	int32_t touch_id;
-
 	struct {
 		struct wl_signal map;
 		struct wl_signal unmap;
@@ -105,40 +103,46 @@ struct wlr_drag_icon {
 	} events;
 
 	struct wl_listener surface_destroy;
-	struct wl_listener seat_client_destroy;
 
 	void *data;
 };
 
+enum wlr_drag_grab_type {
+	WLR_DRAG_GRAB_KEYBOARD,
+	WLR_DRAG_GRAB_KEYBOARD_POINTER,
+	WLR_DRAG_GRAB_KEYBOARD_TOUCH,
+};
+
 struct wlr_drag {
-	struct wlr_seat_pointer_grab pointer_grab;
+	enum wlr_drag_grab_type grab_type;
 	struct wlr_seat_keyboard_grab keyboard_grab;
+	struct wlr_seat_pointer_grab pointer_grab;
 	struct wlr_seat_touch_grab touch_grab;
 
 	struct wlr_seat *seat;
 	struct wlr_seat_client *seat_client;
 	struct wlr_seat_client *focus_client;
 
-	bool is_pointer_grab;
+	struct wlr_drag_icon *icon; // can be NULL
+	struct wlr_surface *focus; // can be NULL
+	struct wlr_data_source *source; // can be NULL
 
-	struct wlr_drag_icon *icon;
-	struct wlr_surface *focus;
-	struct wlr_data_source *source;
+	bool started, dropped, cancelling;
+	int32_t grab_touch_id, touch_id; // if WLR_DRAG_GRAB_TOUCH
 
-	bool cancelling;
-	int32_t grab_touch_id;
+	struct {
+		struct wl_signal focus;
+		struct wl_signal motion; // wlr_drag_motion_event
+		struct wl_signal drop; // wlr_drag_drop_event
+		struct wl_signal destroy;
+	} events;
 
 	struct wl_listener point_destroy;
 	struct wl_listener source_destroy;
 	struct wl_listener seat_client_destroy;
 	struct wl_listener icon_destroy;
 
-	struct {
-		struct wl_signal focus;
-		struct wl_signal motion;
-		struct wl_signal drop;
-		struct wl_signal destroy;
-	} events;
+	void *data;
 };
 
 struct wlr_drag_motion_event {
@@ -179,6 +183,40 @@ void wlr_seat_set_selection(struct wlr_seat *seat,
 	struct wlr_data_source *source, uint32_t serial);
 
 /**
+ * Creates a new drag. To request to start the drag, call
+ * `wlr_seat_request_start_drag`.
+ */
+struct wlr_drag *wlr_drag_create(struct wlr_seat_client *seat_client,
+	struct wlr_data_source *source, struct wlr_surface *icon_surface);
+
+/**
+ * Requests a drag to be started on the seat.
+ */
+void wlr_seat_request_start_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+	struct wlr_surface *origin, uint32_t serial);
+
+/**
+ * Starts a drag on the seat. This starts an implicit keyboard grab, but doesn't
+ * start a pointer or a touch grab.
+ */
+void wlr_seat_start_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+	uint32_t serial);
+
+/**
+ * Starts a pointer drag on the seat. This starts implicit keyboard and pointer
+ * grabs.
+ */
+void wlr_seat_start_pointer_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+	uint32_t serial);
+
+/**
+ * Starts a touch drag on the seat. This starts implicit keyboard and touch
+ * grabs.
+ */
+void wlr_seat_start_touch_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+	uint32_t serial, struct wlr_touch_point *point);
+
+/**
  * Initializes the data source with the provided implementation.
  */
 void wlr_data_source_init(struct wlr_data_source *source,
diff --git a/include/wlr/types/wlr_seat.h b/include/wlr/types/wlr_seat.h
index c81c2cec..c020dbdb 100644
--- a/include/wlr/types/wlr_seat.h
+++ b/include/wlr/types/wlr_seat.h
@@ -191,7 +191,6 @@ struct wlr_seat {
 	struct wl_global *global;
 	struct wl_display *display;
 	struct wl_list clients;
-	struct wl_list drag_icons; // wlr_drag_icon::link
 
 	char *name;
 	uint32_t capabilities;
@@ -239,8 +238,9 @@ struct wlr_seat {
 		struct wl_signal request_set_primary_selection;
 		struct wl_signal set_primary_selection;
 
+		// wlr_seat_request_start_drag_event
+		struct wl_signal request_start_drag;
 		struct wl_signal start_drag; // wlr_drag
-		struct wl_signal new_drag_icon; // wlr_drag_icon
 
 		struct wl_signal destroy;
 	} events;
@@ -265,6 +265,12 @@ struct wlr_seat_request_set_primary_selection_event {
 	uint32_t serial;
 };
 
+struct wlr_seat_request_start_drag_event {
+	struct wlr_drag *drag;
+	struct wlr_surface *origin;
+	uint32_t serial;
+};
+
 struct wlr_seat_pointer_focus_change_event {
 	struct wlr_seat *seat;
 	struct wlr_surface *old_surface, *new_surface;
@@ -597,9 +603,30 @@ bool wlr_seat_touch_has_grab(struct wlr_seat *seat);
  */
 bool wlr_seat_validate_grab_serial(struct wlr_seat *seat, uint32_t serial);
 
+/**
+ * Check whether this serial is valid to start a pointer grab action.
+ */
+bool wlr_seat_validate_pointer_grab_serial(struct wlr_seat *seat,
+	struct wlr_surface *origin, uint32_t serial);
+
+/**
+ * Check whether this serial is valid to start a touch grab action. If it's the
+ * case and point_ptr is non-NULL, *point_ptr is set to the touch point matching
+ * the serial.
+ */
+bool wlr_seat_validate_touch_grab_serial(struct wlr_seat *seat,
+	struct wlr_surface *origin, uint32_t serial,
+	struct wlr_touch_point **point_ptr);
+
+/**
+ * Get a seat client from a seat resource. Returns NULL if inert.
+ */
 struct wlr_seat_client *wlr_seat_client_from_resource(
 	struct wl_resource *resource);
 
+/**
+ * Get a seat client from a pointer resource. Returns NULL if inert.
+ */
 struct wlr_seat_client *wlr_seat_client_from_pointer_resource(
 	struct wl_resource *resource);
 
diff --git a/rootston/seat.c b/rootston/seat.c
index 385cf401..b9392ac4 100644
--- a/rootston/seat.c
+++ b/rootston/seat.c
@@ -603,10 +603,38 @@ static void roots_drag_icon_handle_destroy(struct wl_listener *listener,
 	free(icon);
 }
 
-static void roots_seat_handle_new_drag_icon(struct wl_listener *listener,
+static void roots_seat_handle_request_start_drag(struct wl_listener *listener,
 		void *data) {
-	struct roots_seat *seat = wl_container_of(listener, seat, new_drag_icon);
-	struct wlr_drag_icon *wlr_drag_icon = data;
+	struct roots_seat *seat =
+		wl_container_of(listener, seat, request_start_drag);
+	struct wlr_seat_request_start_drag_event *event = data;
+
+	if (wlr_seat_validate_pointer_grab_serial(seat->seat,
+			event->origin, event->serial)) {
+		wlr_seat_start_pointer_drag(seat->seat, event->drag, event->serial);
+		return;
+	}
+
+	struct wlr_touch_point *point;
+	if (wlr_seat_validate_touch_grab_serial(seat->seat,
+			event->origin, event->serial, &point)) {
+		wlr_seat_start_touch_drag(seat->seat, event->drag, event->serial, point);
+		return;
+	}
+
+	wlr_log(WLR_DEBUG, "Ignoring start_drag request: "
+		"could not validate pointer or touch serial %" PRIu32, event->serial);
+	wlr_data_source_destroy(event->drag->source);
+}
+
+static void roots_seat_handle_start_drag(struct wl_listener *listener,
+		void *data) {
+	struct roots_seat *seat = wl_container_of(listener, seat, start_drag);
+	struct wlr_drag *wlr_drag = data;
+	struct wlr_drag_icon *wlr_drag_icon = wlr_drag->icon;
+	if (wlr_drag_icon == NULL) {
+		return;
+	}
 
 	struct roots_drag_icon *icon = calloc(1, sizeof(struct roots_drag_icon));
 	if (icon == NULL) {
@@ -649,20 +677,27 @@ static void roots_seat_handle_request_set_primary_selection(
 void roots_drag_icon_update_position(struct roots_drag_icon *icon) {
 	roots_drag_icon_damage_whole(icon);
 
-	struct wlr_drag_icon *wlr_icon = icon->wlr_drag_icon;
 	struct roots_seat *seat = icon->seat;
-	struct wlr_cursor *cursor = seat->cursor->cursor;
-	if (wlr_icon->is_pointer) {
+	struct wlr_drag *wlr_drag = icon->wlr_drag_icon->drag;
+	assert(wlr_drag != NULL);
+
+	switch (seat->seat->drag->grab_type) {
+	case WLR_DRAG_GRAB_KEYBOARD:
+		assert(false);
+	case WLR_DRAG_GRAB_KEYBOARD_POINTER:;
+		struct wlr_cursor *cursor = seat->cursor->cursor;
 		icon->x = cursor->x;
 		icon->y = cursor->y;
-	} else {
+		break;
+	case WLR_DRAG_GRAB_KEYBOARD_TOUCH:;
 		struct wlr_touch_point *point =
-			wlr_seat_touch_get_point(seat->seat, wlr_icon->touch_id);
+			wlr_seat_touch_get_point(seat->seat, wlr_drag->touch_id);
 		if (point == NULL) {
 			return;
 		}
 		icon->x = seat->touch_x;
 		icon->y = seat->touch_y;
+		break;
 	}
 
 	roots_drag_icon_damage_whole(icon);
@@ -738,8 +773,11 @@ struct roots_seat *roots_seat_create(struct roots_input *input, char *name) {
 		roots_seat_handle_request_set_primary_selection;
 	wl_signal_add(&seat->seat->events.request_set_primary_selection,
 		&seat->request_set_primary_selection);
-	seat->new_drag_icon.notify = roots_seat_handle_new_drag_icon;
-	wl_signal_add(&seat->seat->events.new_drag_icon, &seat->new_drag_icon);
+	seat->request_start_drag.notify = roots_seat_handle_request_start_drag;
+	wl_signal_add(&seat->seat->events.request_start_drag,
+		&seat->request_start_drag);
+	seat->start_drag.notify = roots_seat_handle_start_drag;
+	wl_signal_add(&seat->seat->events.start_drag, &seat->start_drag);
 	seat->destroy.notify = roots_seat_handle_destroy;
 	wl_signal_add(&seat->seat->events.destroy, &seat->destroy);
 
diff --git a/types/data_device/wlr_data_device.c b/types/data_device/wlr_data_device.c
index 36a9d1b8..d494cf75 100644
--- a/types/data_device/wlr_data_device.c
+++ b/types/data_device/wlr_data_device.c
@@ -73,8 +73,8 @@ static void data_device_start_drag(struct wl_client *client,
 
 	struct wlr_data_source *wlr_source =
 		source != NULL ? &source->source : NULL;
-	if (!seat_client_start_drag(seat_client, wlr_source, icon,
-			origin, serial)) {
+	struct wlr_drag *drag = wlr_drag_create(seat_client, wlr_source, icon);
+	if (drag == NULL) {
 		wl_resource_post_no_memory(device_resource);
 		return;
 	}
@@ -82,6 +82,8 @@ static void data_device_start_drag(struct wl_client *client,
 	if (source != NULL) {
 		source->finalized = true;
 	}
+
+	wlr_seat_request_start_drag(seat_client->seat, drag, origin, serial);
 }
 
 static void data_device_release(struct wl_client *client,
diff --git a/types/data_device/wlr_data_offer.c b/types/data_device/wlr_data_offer.c
index 0b0332b1..086feb11 100644
--- a/types/data_device/wlr_data_offer.c
+++ b/types/data_device/wlr_data_offer.c
@@ -111,20 +111,6 @@ static void data_offer_dnd_finish(struct wlr_data_offer *offer) {
 
 static void data_offer_handle_destroy(struct wl_client *client,
 		struct wl_resource *resource) {
-	struct wlr_data_offer *offer = data_offer_from_resource(resource);
-	if (offer == NULL) {
-		goto out;
-	}
-
-	// If the drag destination has version < 3, wl_data_offer.finish
-	// won't be called, so do this here as a safety net, because
-	// we still want the version >= 3 drag source to be happy.
-	if (wl_resource_get_version(offer->resource) <
-			WL_DATA_OFFER_ACTION_SINCE_VERSION) {
-		data_offer_dnd_finish(offer);
-	}
-
-out:
 	wl_resource_destroy(resource);
 }
 
@@ -135,6 +121,27 @@ static void data_offer_handle_finish(struct wl_client *client,
 		return;
 	}
 
+	// TODO: also fail while we have a drag-and-drop grab
+	if (offer->type != WLR_DATA_OFFER_DRAG) {
+		wl_resource_post_error(offer->resource,
+			WL_DATA_OFFER_ERROR_INVALID_FINISH, "Offer is not drag-and-drop");
+		return;
+	}
+	if (!offer->source->accepted) {
+		wl_resource_post_error(offer->resource,
+			WL_DATA_OFFER_ERROR_INVALID_FINISH, "Premature finish request");
+		return;
+	}
+	enum wl_data_device_manager_dnd_action action =
+		offer->source->current_dnd_action;
+	if (action == WL_DATA_DEVICE_MANAGER_DND_ACTION_NONE ||
+			action == WL_DATA_DEVICE_MANAGER_DND_ACTION_ASK) {
+		wl_resource_post_error(offer->resource,
+			WL_DATA_OFFER_ERROR_INVALID_FINISH,
+			"Offer finished with an invalid action");
+		return;
+	}
+
 	data_offer_dnd_finish(offer);
 	data_offer_destroy(offer);
 }
@@ -183,6 +190,18 @@ void data_offer_destroy(struct wlr_data_offer *offer) {
 	wl_list_remove(&offer->source_destroy.link);
 	wl_list_remove(&offer->link);
 
+	if (offer->type == WLR_DATA_OFFER_DRAG) {
+		// If the drag destination has version < 3, wl_data_offer.finish
+		// won't be called, so do this here as a safety net, because
+		// we still want the version >= 3 drag source to be happy.
+		if (wl_resource_get_version(offer->resource) <
+				WL_DATA_OFFER_ACTION_SINCE_VERSION) {
+			data_offer_dnd_finish(offer);
+		} else if (offer->source && offer->source->impl->dnd_finish) {
+			wlr_data_source_destroy(offer->source);
+		}
+	}
+
 	// Make the resource inert
 	wl_resource_set_user_data(offer->resource, NULL);
 
@@ -206,6 +225,8 @@ static void data_offer_handle_source_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_data_offer *offer =
 		wl_container_of(listener, offer, source_destroy);
+	// Prevent data_offer_destroy from destroying the source again
+	offer->source = NULL;
 	data_offer_destroy(offer);
 }
 
diff --git a/types/data_device/wlr_drag.c b/types/data_device/wlr_drag.c
index fdfabdcf..ab0005d3 100644
--- a/types/data_device/wlr_drag.c
+++ b/types/data_device/wlr_drag.c
@@ -28,6 +28,20 @@ static void drag_set_focus(struct wlr_drag *drag,
 	if (drag->focus_client) {
 		wl_list_remove(&drag->seat_client_destroy.link);
 
+		// If we're switching focus to another client, we want to destroy all
+		// offers without destroying the source. If the drag operation ends, we
+		// want to keep the offer around for the data transfer.
+		struct wlr_data_offer *offer, *tmp;
+		wl_list_for_each_safe(offer, tmp,
+				&drag->focus_client->seat->drag_offers, link) {
+			struct wl_client *client = wl_resource_get_client(offer->resource);
+			if (!drag->dropped && offer->source == drag->source &&
+					client == drag->focus_client->client) {
+				offer->source = NULL;
+				data_offer_destroy(offer);
+			}
+		}
+
 		struct wl_resource *resource;
 		wl_resource_for_each(resource, &drag->focus_client->data_devices) {
 			wl_data_device_send_leave(resource);
@@ -37,20 +51,20 @@ static void drag_set_focus(struct wlr_drag *drag,
 		drag->focus = NULL;
 	}
 
-	if (!surface || !surface->resource) {
-		return;
+	if (!surface) {
+		goto out;
 	}
 
 	if (!drag->source &&
 			wl_resource_get_client(surface->resource) !=
 			drag->seat_client->client) {
-		return;
+		goto out;
 	}
 
 	struct wlr_seat_client *focus_client = wlr_seat_client_for_wl_client(
 		drag->seat_client->seat, wl_resource_get_client(surface->resource));
 	if (!focus_client) {
-		return;
+		goto out;
 	}
 
 	if (drag->source != NULL) {
@@ -88,6 +102,7 @@ static void drag_set_focus(struct wlr_drag *drag,
 	drag->seat_client_destroy.notify = drag_handle_seat_client_destroy;
 	wl_signal_add(&focus_client->events.destroy, &drag->seat_client_destroy);
 
+out:
 	wlr_signal_emit_safe(&drag->events.focus, drag);
 }
 
@@ -101,33 +116,41 @@ static void drag_icon_set_mapped(struct wlr_drag_icon *icon, bool mapped) {
 	}
 }
 
-static void drag_end(struct wlr_drag *drag) {
-	if (!drag->cancelling) {
-		drag->cancelling = true;
-		if (drag->is_pointer_grab) {
+static void drag_icon_destroy(struct wlr_drag_icon *icon);
+
+static void drag_destroy(struct wlr_drag *drag) {
+	if (drag->cancelling) {
+		return;
+	}
+	drag->cancelling = true;
+
+	wlr_signal_emit_safe(&drag->events.destroy, drag);
+
+	if (drag->started) {
+		wlr_seat_keyboard_end_grab(drag->seat);
+		switch (drag->grab_type) {
+		case WLR_DRAG_GRAB_KEYBOARD:
+			break;
+		case WLR_DRAG_GRAB_KEYBOARD_POINTER:
 			wlr_seat_pointer_end_grab(drag->seat);
-		} else {
+			break;
+		case WLR_DRAG_GRAB_KEYBOARD_TOUCH:
 			wlr_seat_touch_end_grab(drag->seat);
-		}
-		wlr_seat_keyboard_end_grab(drag->seat);
-
-		if (drag->source) {
-			wl_list_remove(&drag->source_destroy.link);
+			break;
 		}
 
 		drag_set_focus(drag, NULL, 0, 0);
 
-		if (drag->icon) {
-			wl_list_remove(&drag->icon_destroy.link);
-			drag_icon_set_mapped(drag->icon, false);
-		}
-
 		assert(drag->seat->drag == drag);
 		drag->seat->drag = NULL;
+	}
 
-		wlr_signal_emit_safe(&drag->events.destroy, drag);
-		free(drag);
+	if (drag->source) {
+		wl_list_remove(&drag->source_destroy.link);
 	}
+
+	drag_icon_destroy(drag->icon);
+	free(drag);
 }
 
 static void drag_handle_pointer_enter(struct wlr_seat_pointer_grab *grab,
@@ -156,6 +179,26 @@ static void drag_handle_pointer_motion(struct wlr_seat_pointer_grab *grab,
 	}
 }
 
+static void drag_drop(struct wlr_drag *drag, uint32_t time) {
+	assert(drag->focus_client);
+
+	drag->dropped = true;
+
+	struct wl_resource *resource;
+	wl_resource_for_each(resource, &drag->focus_client->data_devices) {
+		wl_data_device_send_drop(resource);
+	}
+	if (drag->source) {
+		wlr_data_source_dnd_drop(drag->source);
+	}
+
+	struct wlr_drag_drop_event event = {
+		.drag = drag,
+		.time = time,
+	};
+	wlr_signal_emit_safe(&drag->events.drop, &event);
+}
+
 static uint32_t drag_handle_pointer_button(struct wlr_seat_pointer_grab *grab,
 		uint32_t time, uint32_t button, uint32_t state) {
 	struct wlr_drag *drag = grab->data;
@@ -165,17 +208,7 @@ static uint32_t drag_handle_pointer_button(struct wlr_seat_pointer_grab *grab,
 			state == WL_POINTER_BUTTON_STATE_RELEASED) {
 		if (drag->focus_client && drag->source->current_dnd_action &&
 				drag->source->accepted) {
-			struct wl_resource *resource;
-			wl_resource_for_each(resource, &drag->focus_client->data_devices) {
-				wl_data_device_send_drop(resource);
-			}
-			wlr_data_source_dnd_drop(drag->source);
-
-			struct wlr_drag_drop_event event = {
-				.drag = drag,
-				.time = time,
-			};
-			wlr_signal_emit_safe(&drag->events.drop, &event);
+			drag_drop(drag, time);
 		} else if (drag->source->impl->dnd_finish) {
 			// This will end the grab and free `drag`
 			wlr_data_source_destroy(drag->source);
@@ -185,7 +218,7 @@ static uint32_t drag_handle_pointer_button(struct wlr_seat_pointer_grab *grab,
 
 	if (grab->seat->pointer_state.button_count == 0 &&
 			state == WL_POINTER_BUTTON_STATE_RELEASED) {
-		drag_end(drag);
+		drag_destroy(drag);
 	}
 
 	return 0;
@@ -199,7 +232,7 @@ static void drag_handle_pointer_axis(struct wlr_seat_pointer_grab *grab,
 
 static void drag_handle_pointer_cancel(struct wlr_seat_pointer_grab *grab) {
 	struct wlr_drag *drag = grab->data;
-	drag_end(drag);
+	drag_destroy(drag);
 }
 
 static const struct wlr_pointer_grab_interface
@@ -225,13 +258,10 @@ static void drag_handle_touch_up(struct wlr_seat_touch_grab *grab,
 	}
 
 	if (drag->focus_client) {
-		struct wl_resource *resource;
-		wl_resource_for_each(resource, &drag->focus_client->data_devices) {
-			wl_data_device_send_drop(resource);
-		}
+		drag_drop(drag, time);
 	}
 
-	drag_end(drag);
+	drag_destroy(drag);
 }
 
 static void drag_handle_touch_motion(struct wlr_seat_touch_grab *grab,
@@ -255,7 +285,7 @@ static void drag_handle_touch_enter(struct wlr_seat_touch_grab *grab,
 
 static void drag_handle_touch_cancel(struct wlr_seat_touch_grab *grab) {
 	struct wlr_drag *drag = grab->data;
-	drag_end(drag);
+	drag_destroy(drag);
 }
 
 static const struct wlr_touch_grab_interface
@@ -287,7 +317,7 @@ static void drag_handle_keyboard_modifiers(struct wlr_seat_keyboard_grab *grab,
 
 static void drag_handle_keyboard_cancel(struct wlr_seat_keyboard_grab *grab) {
 	struct wlr_drag *drag = grab->data;
-	drag_end(drag);
+	drag_destroy(drag);
 }
 
 static const struct wlr_keyboard_grab_interface
@@ -306,7 +336,7 @@ static void drag_handle_icon_destroy(struct wl_listener *listener, void *data) {
 static void drag_handle_drag_source_destroy(struct wl_listener *listener,
 		void *data) {
 	struct wlr_drag *drag = wl_container_of(listener, drag, source_destroy);
-	drag_end(drag);
+	drag_destroy(drag);
 }
 
 
@@ -318,8 +348,6 @@ static void drag_icon_destroy(struct wlr_drag_icon *icon) {
 	wlr_signal_emit_safe(&icon->events.destroy, icon);
 	icon->surface->role_data = NULL;
 	wl_list_remove(&icon->surface_destroy.link);
-	wl_list_remove(&icon->seat_client_destroy.link);
-	wl_list_remove(&icon->link);
 	free(icon);
 }
 
@@ -345,26 +373,15 @@ const struct wlr_surface_role drag_icon_surface_role = {
 	.commit = drag_icon_surface_role_commit,
 };
 
-static void drag_icon_handle_seat_client_destroy(struct wl_listener *listener,
-		void *data) {
-	struct wlr_drag_icon *icon =
-		wl_container_of(listener, icon, seat_client_destroy);
-
-	drag_icon_destroy(icon);
-}
-
-static struct wlr_drag_icon *drag_icon_create(
-		struct wlr_surface *icon_surface, struct wlr_seat_client *client,
-		bool is_pointer, int32_t touch_id) {
+static struct wlr_drag_icon *drag_icon_create(struct wlr_drag *drag,
+		struct wlr_surface *surface) {
 	struct wlr_drag_icon *icon = calloc(1, sizeof(struct wlr_drag_icon));
 	if (!icon) {
 		return NULL;
 	}
 
-	icon->surface = icon_surface;
-	icon->client = client;
-	icon->is_pointer = is_pointer;
-	icon->touch_id = touch_id;
+	icon->drag = drag;
+	icon->surface = surface;
 
 	wl_signal_init(&icon->events.map);
 	wl_signal_init(&icon->events.unmap);
@@ -373,15 +390,9 @@ static struct wlr_drag_icon *drag_icon_create(
 	wl_signal_add(&icon->surface->events.destroy, &icon->surface_destroy);
 	icon->surface_destroy.notify = drag_icon_handle_surface_destroy;
 
-	wl_signal_add(&client->events.destroy, &icon->seat_client_destroy);
-	icon->seat_client_destroy.notify = drag_icon_handle_seat_client_destroy;
-
 	icon->surface->role_data = icon;
 
-	wl_list_insert(&client->seat->drag_icons, &icon->link);
-	wlr_signal_emit_safe(&client->seat->events.new_drag_icon, icon);
-
-	if (wlr_surface_has_buffer(icon_surface)) {
+	if (wlr_surface_has_buffer(surface)) {
 		drag_icon_set_mapped(icon, true);
 	}
 
@@ -389,20 +400,11 @@ static struct wlr_drag_icon *drag_icon_create(
 }
 
 
-static void seat_handle_drag_source_destroy(struct wl_listener *listener,
-		void *data) {
-	struct wlr_seat *seat =
-		wl_container_of(listener, seat, drag_source_destroy);
-	wl_list_remove(&seat->drag_source_destroy.link);
-	seat->drag_source = NULL;
-}
-
-bool seat_client_start_drag(struct wlr_seat_client *client,
-		struct wlr_data_source *source, struct wlr_surface *icon_surface,
-		struct wlr_surface *origin, uint32_t serial) {
+struct wlr_drag *wlr_drag_create(struct wlr_seat_client *seat_client,
+		struct wlr_data_source *source, struct wlr_surface *icon_surface) {
 	struct wlr_drag *drag = calloc(1, sizeof(struct wlr_drag));
 	if (drag == NULL) {
-		return false;
+		return NULL;
 	}
 
 	wl_signal_init(&drag->events.focus);
@@ -410,51 +412,18 @@ bool seat_client_start_drag(struct wlr_seat_client *client,
 	wl_signal_init(&drag->events.drop);
 	wl_signal_init(&drag->events.destroy);
 
-	struct wlr_seat *seat = client->seat;
-	drag->seat = seat;
-
-	drag->is_pointer_grab = !wl_list_empty(&client->pointers) &&
-		seat->pointer_state.button_count == 1 &&
-		seat->pointer_state.grab_serial == serial &&
-		seat->pointer_state.focused_surface &&
-		seat->pointer_state.focused_surface == origin;
-
-	bool is_touch_grab = !wl_list_empty(&client->touches) &&
-		wlr_seat_touch_num_points(seat) == 1 &&
-		seat->touch_state.grab_serial == serial;
-
-	// set in the iteration
-	struct wlr_touch_point *point = NULL;
-	if (is_touch_grab) {
-		wl_list_for_each(point, &seat->touch_state.touch_points, link) {
-			is_touch_grab = point->surface && point->surface == origin;
-			break;
-		}
-	}
-
-	if (!drag->is_pointer_grab && !is_touch_grab) {
-		free(drag);
-		return true;
-	}
-
-	if (seat->drag != NULL) {
-		wlr_log(WLR_DEBUG, "Refusing to start drag, "
-			"another drag is already in progress");
-		free(drag);
-		return true;
-	}
+	drag->seat = seat_client->seat;
+	drag->seat_client = seat_client;
 
 	if (icon_surface) {
-		int32_t touch_id = (point ? point->touch_id : 0);
-		struct wlr_drag_icon *icon =
-			drag_icon_create(icon_surface, client, drag->is_pointer_grab,
-				touch_id);
-		if (!icon) {
+		struct wlr_drag_icon *icon = drag_icon_create(drag, icon_surface);
+		if (icon == NULL) {
 			free(drag);
-			return false;
+			return NULL;
 		}
 
 		drag->icon = icon;
+
 		drag->icon_destroy.notify = drag_handle_icon_destroy;
 		wl_signal_add(&icon->events.destroy, &drag->icon_destroy);
 	}
@@ -465,41 +434,85 @@ bool seat_client_start_drag(struct wlr_seat_client *client,
 		wl_signal_add(&source->events.destroy, &drag->source_destroy);
 	}
 
-	drag->seat_client = client;
 	drag->pointer_grab.data = drag;
 	drag->pointer_grab.interface = &data_device_pointer_drag_interface;
 
 	drag->touch_grab.data = drag;
 	drag->touch_grab.interface = &data_device_touch_drag_interface;
-	drag->grab_touch_id = seat->touch_state.grab_id;
 
 	drag->keyboard_grab.data = drag;
 	drag->keyboard_grab.interface = &data_device_keyboard_drag_interface;
 
-	wlr_seat_keyboard_start_grab(seat, &drag->keyboard_grab);
+	return drag;
+}
+
+void wlr_seat_request_start_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+		struct wlr_surface *origin, uint32_t serial) {
+	assert(drag->seat == seat);
 
-	if (drag->is_pointer_grab) {
-		wlr_seat_pointer_clear_focus(seat);
-		wlr_seat_pointer_start_grab(seat, &drag->pointer_grab);
-	} else {
-		assert(point);
-		wlr_seat_touch_start_grab(seat, &drag->touch_grab);
-		drag_set_focus(drag, point->surface, point->sx, point->sy);
+	if (seat->drag != NULL) {
+		wlr_log(WLR_DEBUG, "Rejecting start_drag request, "
+			"another drag-and-drop operation is already in progress");
+		return;
 	}
 
+	struct wlr_seat_request_start_drag_event event = {
+		.drag = drag,
+		.origin = origin,
+		.serial = serial,
+	};
+	wlr_signal_emit_safe(&seat->events.request_start_drag, &event);
+}
+
+static void seat_handle_drag_source_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_seat *seat =
+		wl_container_of(listener, seat, drag_source_destroy);
+	wl_list_remove(&seat->drag_source_destroy.link);
+	seat->drag_source = NULL;
+}
+
+void wlr_seat_start_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+		uint32_t serial) {
+	assert(drag->seat == seat);
+	assert(!drag->started);
+	drag->started = true;
+
+	wlr_seat_keyboard_start_grab(seat, &drag->keyboard_grab);
+
 	seat->drag = drag;
 	seat->drag_serial = serial;
 
 	// We need to destroy the previous source, because listeners only expect one
 	// active drag source at a time.
 	wlr_data_source_destroy(seat->drag_source);
-	seat->drag_source = source;
-	if (source != NULL) {
+	seat->drag_source = drag->source;
+	if (drag->source != NULL) {
 		seat->drag_source_destroy.notify = seat_handle_drag_source_destroy;
-		wl_signal_add(&source->events.destroy, &seat->drag_source_destroy);
+		wl_signal_add(&drag->source->events.destroy, &seat->drag_source_destroy);
 	}
 
 	wlr_signal_emit_safe(&seat->events.start_drag, drag);
+}
+
+void wlr_seat_start_pointer_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+		uint32_t serial) {
+	drag->grab_type = WLR_DRAG_GRAB_KEYBOARD_POINTER;
+
+	wlr_seat_pointer_clear_focus(seat);
+	wlr_seat_pointer_start_grab(seat, &drag->pointer_grab);
+
+	wlr_seat_start_drag(seat, drag, serial);
+}
+
+void wlr_seat_start_touch_drag(struct wlr_seat *seat, struct wlr_drag *drag,
+		uint32_t serial, struct wlr_touch_point *point) {
+	drag->grab_type = WLR_DRAG_GRAB_KEYBOARD_TOUCH;
+	drag->grab_touch_id = seat->touch_state.grab_id;
+	drag->touch_id = point->touch_id;
+
+	wlr_seat_touch_start_grab(seat, &drag->touch_grab);
+	drag_set_focus(drag, point->surface, point->sx, point->sy);
 
-	return true;
+	wlr_seat_start_drag(seat, drag, serial);
 }
diff --git a/types/seat/wlr_seat.c b/types/seat/wlr_seat.c
index 3595be15..b5f1d540 100644
--- a/types/seat/wlr_seat.c
+++ b/types/seat/wlr_seat.c
@@ -266,12 +266,11 @@ struct wlr_seat *wlr_seat_create(struct wl_display *display, const char *name) {
 	seat->display = display;
 	seat->name = strdup(name);
 	wl_list_init(&seat->clients);
-	wl_list_init(&seat->drag_icons);
 	wl_list_init(&seat->selection_offers);
 	wl_list_init(&seat->drag_offers);
 
+	wl_signal_init(&seat->events.request_start_drag);
 	wl_signal_init(&seat->events.start_drag);
-	wl_signal_init(&seat->events.new_drag_icon);
 
 	wl_signal_init(&seat->events.request_set_cursor);
 
diff --git a/types/seat/wlr_seat_pointer.c b/types/seat/wlr_seat_pointer.c
index 31901716..d03385cf 100644
--- a/types/seat/wlr_seat_pointer.c
+++ b/types/seat/wlr_seat_pointer.c
@@ -402,3 +402,17 @@ void seat_client_destroy_pointer(struct wl_resource *resource) {
 	}
 	wl_resource_set_user_data(resource, NULL);
 }
+
+bool wlr_seat_validate_pointer_grab_serial(struct wlr_seat *seat,
+		struct wlr_surface *origin, uint32_t serial) {
+	if (seat->pointer_state.button_count != 1 ||
+			seat->pointer_state.grab_serial != serial) {
+		return false;
+	}
+
+	if (origin != NULL && seat->pointer_state.focused_surface != origin) {
+		return false;
+	}
+
+	return true;
+}
diff --git a/types/seat/wlr_seat_touch.c b/types/seat/wlr_seat_touch.c
index d4fa6f0b..486fa55d 100644
--- a/types/seat/wlr_seat_touch.c
+++ b/types/seat/wlr_seat_touch.c
@@ -359,3 +359,24 @@ void seat_client_destroy_touch(struct wl_resource *resource) {
 	}
 	wl_resource_set_user_data(resource, NULL);
 }
+
+bool wlr_seat_validate_touch_grab_serial(struct wlr_seat *seat,
+		struct wlr_surface *origin, uint32_t serial,
+		struct wlr_touch_point **point_ptr) {
+	if (wlr_seat_touch_num_points(seat) != 1 ||
+			seat->touch_state.grab_serial != serial) {
+		return false;
+	}
+
+	struct wlr_touch_point *point;
+	wl_list_for_each(point, &seat->touch_state.touch_points, link) {
+		if (origin == NULL || point->surface == origin) {
+			if (point_ptr != NULL) {
+				*point_ptr = point;
+			}
+			return true;
+		}
+	}
+
+	return false;
+}