Qt-based media player

This patch implements a simple Qt-based media player which is actually a
graphical user interface for the SDL-based 'avplay' media player from
'libav'. It starts 'avplay' as a child and shows its graphical output in a
'QNitpickerViewWidget'. The widgets for controlling the player state send
the according keyboard and mouse input events to 'avplay'.

The 'qt_avplay' player supports the following configuration options:

<mediafile name="..."/>
-> name of the media file to play

<framebuffer_filter name="..." ram_quota="..."/> (may appear multiple times)
-> name of a framebuffer filter service to filter the video output

Fixes #222.

os/include/input/event_queue.h

@@ -0,0 +1,70 @@
+/*
+ * \brief  Input event queue
+ * \author Norman Feske
+ * \date   2007-10-08
+ */
+
+/*
+ * Copyright (C) 2007-2012 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _EVENT_QUEUE_H_
+#define _EVENT_QUEUE_H_
+
+#include <base/printf.h>
+#include <input/event.h>
+#include <os/ring_buffer.h>
+
+/**
+ * Input event queue
+ *
+ * We expect the client to fetch events circa each 10ms. The PS/2 driver queues
+ * up to 255 events, which should be enough. Normally, PS/2 generates not more
+ * than 16Kbit/s, which would correspond to ca. 66 mouse events per 10ms.
+ */
+class Event_queue
+{
+	private:
+
+		bool                           _enabled;
+		Ring_buffer<Input::Event, 512> _ev_queue;
+
+	public:
+
+		Event_queue() : _enabled(false), _ev_queue() { }
+
+		void enable()  { _enabled = true; }
+		void disable() { _enabled = false; }
+
+		void add(Input::Event e)
+		{
+			if (!_enabled) return;
+
+			try {
+				_ev_queue.add(e);
+			} catch (Ring_buffer<Input::Event, 512>::Overflow) {
+				PWRN("event buffer overflow");
+			}
+		}
+
+		Input::Event get()
+		{
+			if (_enabled)
+				return _ev_queue.get();
+			else
+				return Input::Event();
+		}
+
+		bool empty()
+		{
+			if (_enabled)
+				return _ev_queue.empty();
+			else
+				return true;
+		}
+};
+
+#endif /* _EVENT_QUEUE_H_ */