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/src/lib/genode_c_api/event.cc

@@ -0,0 +1,134 @@
+/*
+ * \brief  C interface to Genode's event session
+ * \author Norman Feske
+ * \date   2021-09-29
+ */
+
+/*
+ * Copyright (C) 2021 Genode Labs GmbH
+ *
+ * This file is distributed under the terms of the GNU General Public License
+ * version 2.
+ */
+
+#include <base/registry.h>
+#include <base/log.h>
+#include <base/session_label.h>
+#include <event_session/connection.h>
+#include <genode_c_api/event.h>
+
+using namespace Genode;
+
+static Env                               *_env_ptr;
+static Allocator                         *_alloc_ptr;
+static Registry<Registered<genode_event>> _event_sessions { };
+
+
+struct genode_event : private Noncopyable, private Interface
+{
+	private:
+
+		Env       &_env;
+		Allocator &_alloc;
+
+		Session_label const _session_label;
+
+		Event::Connection _connection { _env, _session_label.string() };
+
+	public:
+
+		genode_event(Env &env, Allocator &alloc,
+		             Session_label const &session_label)
+		:
+			_env(env), _alloc(alloc), _session_label(session_label)
+		{ }
+
+		template <typename FN>
+		void with_batch(FN const &fn)
+		{
+			_connection.with_batch(fn);
+		}
+
+};
+
+
+void genode_event_init(genode_env       *env_ptr,
+                       genode_allocator *alloc_ptr)
+{
+	_env_ptr   = env_ptr;
+	_alloc_ptr = alloc_ptr;
+}
+
+
+namespace {
+
+	struct Submit : genode_event_submit
+	{
+		Event::Session_client::Batch &batch;
+
+		template <typename FN>
+		static void _with_batch(struct genode_event_submit *myself, FN const &fn)
+		{
+			fn(static_cast<Submit *>(myself)->batch);
+		}
+
+		static void _touch(struct genode_event_submit *myself,
+		                   struct genode_event_touch_args const *args)
+		{
+			Input::Touch_id id { (int)args->finger };
+
+			_with_batch(myself, [&] (Event::Session_client::Batch &batch) {
+				batch.submit(Input::Touch { id, (float)args->xpos, (float)args->ypos }); });
+		}
+
+		static void _touch_release(struct genode_event_submit *myself,
+		                           unsigned finger)
+		{
+			Input::Touch_id id { (int)finger };
+
+			_with_batch(myself, [&] (Event::Session_client::Batch &batch) {
+				batch.submit(Input::Touch_release { id }); });
+		}
+
+		Submit(Event::Session_client::Batch &batch)
+		:
+			batch(batch)
+		{
+			touch         = _touch;
+			touch_release = _touch_release;
+		};
+
+	};
+}
+
+
+void genode_event_generate(struct genode_event               *event_session,
+                           genode_event_generator_t           generator_fn,
+                           struct genode_event_generator_ctx *ctx)
+{
+	event_session->with_batch([&] (Event::Session_client::Batch &batch) {
+
+		Submit submit { batch };
+
+		(*generator_fn)(ctx, &submit);
+	});
+}
+
+
+struct genode_event *genode_event_create(struct genode_event_args const *args)
+{
+	if (!_env_ptr || !_alloc_ptr) {
+		error("genode_event_create: missing call of genode_event_init");
+		return nullptr;
+	}
+
+	return new (*_alloc_ptr)
+		Registered<genode_event>(_event_sessions, *_env_ptr, *_alloc_ptr,
+		                         Session_label(args->label));
+}
+
+
+void genode_event_destroy(struct genode_event *event_ptr)
+{
+	destroy(*_alloc_ptr, event_ptr);
+}