WIP: Atomic layout updates ground work

include/sway/desktop/transaction.h

@@ -0,0 +1,56 @@
+#ifndef _SWAY_TRANSACTION_H
+#define _SWAY_TRANSACTION_H
+#include "sway/tree/container.h"
+
+/**
+ * Transactions enable us to perform atomic layout updates.
+ *
+ * When we want to make adjustments to the layout, we create a transaction.
+ * A transaction contains a list of affected containers and their new state.
+ * A state might contain a new size, or new border settings, or new parent/child
+ * relationships.
+ *
+ * Calling transaction_commit() makes sway notify of all the affected clients
+ * with their new sizes. We then wait for all the views to respond with their
+ * new surface sizes. When all are ready, or when a timeout has passed, we apply
+ * the updates all at the same time.
+ */
+
+struct sway_transaction {
+	struct wl_event_source *timer;
+	list_t *instructions;   // struct sway_transaction_instruction *
+	list_t *damage;         // struct wlr_box *
+	size_t num_waiting;
+};
+
+/**
+ * Create a new transaction.
+ */
+struct sway_transaction *transaction_create(void);
+
+/**
+ * Add a container's pending state to the transaction.
+ */
+void transaction_add_container(struct sway_transaction *transaction,
+		struct sway_container *container);
+
+/**
+ * Add a box to be damaged when the transaction is applied.
+ * The box should be in layout coordinates.
+ */
+void transaction_add_damage(struct sway_transaction *transaction,
+		struct wlr_box *box);
+
+/**
+ * Submit a transaction to the client views for configuration.
+ */
+void transaction_commit(struct sway_transaction *transaction);
+
+/**
+ * Notify the transaction system that a view is ready for the new layout.
+ *
+ * When all views in the transaction are ready, the layout will be applied.
+ */
+void transaction_notify_view_ready(struct sway_view *view, uint32_t serial);
+
+#endif