example: Add volume element

https://bugzilla.gnome.org/show_bug.cgi?id=736882

samples/ExampleVolume.cs

@@ -0,0 +1,115 @@
+using GLib;
+using Gst;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace GstreamerSharp
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Application.Init(ref args);
+
+            Element src = ElementFactory.Make("audiotestsrc");
+            Element convert = ElementFactory.Make("audioconvert");
+            Element volume = new ExampleVolume();
+            Element sink = ElementFactory.Make("autoaudiosink");
+
+            Pipeline pipeline = new Pipeline();
+            pipeline.Add(src, convert, volume, sink);
+            Element.Link(src, convert, volume, sink);
+
+            pipeline.SetState(State.Playing);
+
+            MainLoop loop = new MainLoop();
+            loop.Run();
+
+            pipeline.SetState(State.Null);
+
+            Console.ReadLine();
+        }
+    }
+    class ExampleVolume : Element
+    {
+        public ExampleVolume()
+        {
+            Volume = 0.5;
+
+            _sink = new Pad(__sinkTemplate, "sink");
+            _sink.ChainFunctionFull = Chain;
+            _sink.Flags |= PadFlags.ProxyCaps;
+            AddPad(_sink);
+
+            _src = new Pad(__srcTemplate, "src");
+            _src.Flags |= PadFlags.ProxyCaps;
+            AddPad(_src);
+        }
+        
+        public double Volume { get; set; }
+
+        FlowReturn Chain(Pad pad, Gst.Object parent, Gst.Buffer buffer)
+        {
+            if (Volume == 1.0)
+            {
+                return _src.Push(buffer);
+            }
+
+            buffer.MakeWritable();
+
+            MapInfo mapInfo;
+            buffer.Map(out mapInfo, MapFlags.Read | MapFlags.Write);
+
+            ScaleInt16(mapInfo.DataPtr, mapInfo.Size / 2, Volume);
+
+            buffer.Unmap(mapInfo);
+            
+            return _src.Push(buffer);
+        }
+
+        private unsafe void ScaleInt16(IntPtr data, ulong size, double volume)
+        {
+            Int16* sample = (Int16*)data;
+            for (ulong i = 0; i < size; i++)
+            {
+                *sample = ClampInt16(*sample * volume);
+                sample++;
+            }
+        }
+
+        private Int16 ClampInt16(double d)
+        {
+            int i = (int)Math.Round(d);
+
+            if (i > Int16.MaxValue)
+            {
+                return Int16.MaxValue;
+            }
+            else if (i < Int16.MinValue)
+            {
+                return Int16.MinValue;
+            }
+            else
+            {
+                return (Int16)i;
+            }
+        }
+
+        Pad _src;
+        Pad _sink;
+
+        static ExampleVolume()
+        {
+            Caps audioCaps = Caps.FromString("audio/x-raw, format=(string) S16LE, rate=(int) [1, MAX], channels=(int) 2, layout=(string) interleaved");
+            __srcTemplate = new PadTemplate("src", PadDirection.Src, PadPresence.Always, audioCaps);
+            __sinkTemplate = new PadTemplate("sink", PadDirection.Sink, PadPresence.Always, audioCaps);
+        }
+
+        static PadTemplate __srcTemplate;
+        static PadTemplate __sinkTemplate;
+    }
+}