os: introduce C API for generating Genode events

This patch introduces a C API to be used by input drivers to generate
Genode events. The initial version is limited to multitouch events only.

Fixes #4273

repos/os/include/genode_c_api/event.h

@@ -0,0 +1,96 @@
+/*
+ * \brief  C interface to Genode's event session
+ * \author Norman Feske
+ * \date   2021-09-29
+ */
+
+/*
+ * Copyright (C) 2021 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__GENODE_C_API__EVENT_H_
+#define _INCLUDE__GENODE_C_API__EVENT_H_
+
+#include <genode_c_api/base.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Initialize event-session handling
+ */
+void genode_event_init(struct genode_env *,
+                       struct genode_allocator *);
+
+
+struct genode_event;  /* definition is private to the implementation */
+
+
+/****************************
+ ** Event-session lifetime **
+ ****************************/
+
+struct genode_event_args
+{
+	char const *label;
+};
+
+struct genode_event *genode_event_create(struct genode_event_args const *);
+
+void genode_event_destroy(struct genode_event *);
+
+
+/**********************
+ ** Event submission **
+ **********************/
+
+struct genode_event_touch_args
+{
+	unsigned finger;
+	unsigned xpos;
+	unsigned ypos;
+	unsigned width;
+};
+
+
+struct genode_event_submit;
+
+
+/**
+ * Interface called by 'genode_event_generator_t' to submit events
+ */
+struct genode_event_submit
+{
+	void (*touch) (struct genode_event_submit *,
+	               struct genode_event_touch_args const *);
+
+	void (*touch_release) (struct genode_event_submit *, unsigned finger);
+};
+
+
+/**
+ * Context private to 'genode_event_generator_t'
+ */
+struct genode_event_generator_ctx;
+
+
+typedef void (*genode_event_generator_t)
+	(struct genode_event_generator_ctx *, struct genode_event_submit *);
+
+
+/**
+ * Generate batch of events
+ */
+void genode_event_generate(struct genode_event *,
+                           genode_event_generator_t,
+                           struct genode_event_generator_ctx *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _INCLUDE__GENODE_C_API__EVENT_H_ */