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Nifty time savers for WPF development

I just published an article on Code Project, that explains how to use my latest FM USB library for building real world software radio receiver with WPF. There I referenced to some nifty WPF time savers, I’m using for everyday development. So, today I want to share those code pieces with you.

Software radio reciever screenshot

Binding time savers

Want to use following syntax for set binding in code?

Presets.SetBinding(ListBox.ItemsSourceProperty, _device, "Presets");

This piece of code sets binding to Preset DependencyObject, which is Listbox and connects ListBox.ItemsSource dependency property with “Presets” property of CLR object _device. How it done? Simple, as usual

public static BindingExpressionBase SetBinding(this DependencyObject target, DependencyProperty dp, object source, string path) {
   Binding b = new Binding(path);
   b.Source = source;
   return BindingOperations.SetBinding(target, dp, b);

But what to do when we need a converter? Simple:

public static BindingExpressionBase SetBinding(this DependencyObject target, DependencyProperty dp, object source, string path, IValueConverter converter) {
   Binding b = new Binding(path);
   b.Source = source;
   b.Converter = converter;
   return BindingOperations.SetBinding(target, dp, b);

However to use this method, we need to create special object, which implements IValueConverter. Whey not to do it generically? Like this:

SignalTransform.SetBinding(ScaleTransform.ScaleYProperty, _device.RDS,"SignalStrength", new ValueConverter<byte, double>(b => { return 1-(b / 36d); }));

But we need this special handy ValueConverter class. What’s the problem? Here come the king:

public class ValueConverter<TIN, TOUT> : IValueConverter {

   public ValueConverter(Func<TIN, TOUT> forwardConversion) {
      ForwardConversion = forwardConversion;

   public ValueConverter(Func<TIN, TOUT> forwardConversion, Func<TOUT, TIN> reverseConversion) {
      ForwardConversion = forwardConversion;
      ReverseConversion = reverseConversion;

   public Func<TIN, TOUT> ForwardConversion { get; set; }

   public Func<TOUT, TIN> ReverseConversion { get; set; }
   public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
      try {
         var in1 = Object.ReferenceEquals(value, DependencyProperty.UnsetValue) ? default(TIN) : (TIN)value;
         return ForwardConversion(in1);
      } catch {
         return Binding.DoNothing;

   public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
      try {
         var out1 = Object.ReferenceEquals(value, DependencyProperty.UnsetValue) ? default(TOUT) : (TOUT)value;
         return ReverseConversion(out1);
      } catch {
         return Binding.DoNothing;


Isn’t it really simple? But what to do with ugly App.Current.Dispatcher.BeginInvoke((SendOrPostCallback)delegate(object o)…? Use dispatcher time savers.

Dispatcher time savers

Don’t you ever want to do this in order to make context switching between UI thread and other application thread in WPF?

this.Dispatch(() => {… DO SOMETHING IN UI THREAD …};

Now you can (with default and preset DispatcherPriority:

public static DispatcherOperation Dispatch(this DispatcherObject sender, Action callback) { return sender.Dispatch(DispatcherPriority.Normal, callback); }

public static DispatcherOperation Dispatch(this DispatcherObject sender,  DispatcherPriority priority, Action callback) {
   if (sender.Dispatcher == null) return null;
   if (sender.Dispatcher.CheckAccess()) {
      return null;
   } else {
      return sender.Dispatcher.BeginInvoke(priority, callback);

Nice, isn’t it? But what to do if we do not want to set binding, but we do want to be notified about property change of dependency objects?

Bindingless handlers time saver

Let’s assume, that we have “Tune” UIelement, which has Angle property, but not exposes PropertyChanged event (like it done with Rotary custom control by Expression Blend team… Designers, you know… :)

However I want to be able to add handler for Angle dependency property changed event and do something when it changed. Like this:

Tune.AddValueChanged(RotaryControl.RotaryControl.AngleProperty, (s, ex) => {
   _device.Tune(Tune.Angle > _prevTune);
   _prevTune = Tune.Angle;

Here comes our time saver for this purpose:

public static void AddValueChanged(this DependencyObject sender, DependencyProperty property, EventHandler handler) {
   DependencyPropertyDescriptor.FromProperty(property, sender.GetType()).AddValueChanged(sender, handler);

But if we add handler we should be able to remove it too.

public static void RemoveValueChanged(this DependencyObject sender, DependencyProperty property, EventHandler handler) {
   DependencyPropertyDescriptor.FromProperty(property, sender.GetType()).RemoveValueChanged(sender, handler);

Now we done with some of my nifty helpers. And last, but not the least:

All times question: how to scale ranges

Here is how :)

public static double ToRange(this double value, double minSource, double maxSource, double minTarget, double maxTarget) {
   var sr = maxSource – minSource;
   var tr = maxTarget – minTarget;
   var ratio = sr / tr;
   return minTarget+(value / ratio);

Now we can connect them and get something like this:

Volume.AddValueChanged(RotaryControl.RotaryControl.AngleProperty, (s, ex) => {
   DirectSoundMethods.Volume = (int)Volume.Angle.ToRange(Volume.CounterClockwiseMostAngle, Volume.ClockwiseMostAngle, -4000, 0);

Isn’t it brilliant?

Have a good day and be sure to read and rate my last article on Code Project :) Be good people.

Audio CD operation including CD-Text reading in pure C#

Recently we spoke about reading radio data in C#, however as in any vehicle we have also CD players. So what can be better, than to have an ability to play CDs while being notified about track name, gathered from CD-Text?


So, let’s start. First of all, I want to express my pain with MSDN documentation about CD-ROM structure. Documentation team, please, please, please update it. First of all it is no accurate, then there are a ton of things missing. However, “À la guerre comme à la guerre”, thus I invested three days in deep DDK research.

Before we can do anything with CD-ROM, we have to find it. I took the same approach as I used for HID devices. Let’s create a device

[SecurityPermission(SecurityAction.InheritanceDemand, UnmanagedCode = true)]
[SecurityPermission(SecurityAction.Demand, UnmanagedCode = true)]
public class CDDADevice : SafeHandleZeroOrMinusOneIsInvalid, IDisposable, INotifyPropertyChanged {

Internal constructor for security reasons

[SecurityPermission(SecurityAction.Demand, UnmanagedCode = true)]
internal CDDADevice(char drive) : base(true) {

And a find method itself

[SecurityPermission(SecurityAction.Demand, UnmanagedCode = true)]
private void findDevice(char drive) {
   if (Drive == drive) return;
   if (Native.GetDriveType(string.Concat(drive, ":\")) == Native.DRIVE.CDROM) {
      this.handle = Native.CreateFile(string.Concat("\\.\", drive, ‘:’), Native.GENERIC_READ, Native.FILE_SHARE_READ, IntPtr.Zero, Native.OPEN_EXISTING, Native.FILE_ATTRIBUTE_READONLY | Native.FILE_FLAG_SEQUENTIAL_SCAN, IntPtr.Zero);
      if (this.handle.ToInt32() != -1 && this.handle.ToInt32() != 0) this.Drive = drive;

Where GetDriveType and CreateFile are win32 methods with following signatures

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
[DllImport("kernel32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall, SetLastError = true)]
internal static extern DRIVE GetDriveType(string drive);
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
[DllImport("kernel32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall, SetLastError = true)]
internal static extern IntPtr CreateFile(
      string lpFileName,
      uint dwDesiredAccess,
      uint dwShareMode,
      IntPtr SecurityAttributes,
      uint dwCreationDisposition,
      uint dwFlagsAndAttributes,
      IntPtr hTemplateFile);
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
[DllImport("kernel32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall, SetLastError = true)]
internal static extern bool CloseHandle(IntPtr hHandle);

Also, we need some constants

internal enum DRIVE : byte {
   UNKNOWN = 0,

internal const uint GENERIC_READ = 0×80000000;
internal const uint FILE_SHARE_READ = 0×00000001;
internal const uint OPEN_EXISTING = 3;
internal const uint FILE_ATTRIBUTE_READONLY = 0×00000001;
internal const uint FILE_FLAG_SEQUENTIAL_SCAN = 0×08000000;

Now, when we have our cdrom handle in hands, we can read it’s Table Of Content. Now, thing become harder because of the fact, that we have to use very complicated platform method:

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
[DllImport("kernel32.dll", EntryPoint = "DeviceIoControl", SetLastError=true)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool DeviceIoControl(
   [In] IntPtr hDevice,
   IOCTL dwIoControl,
   [In] IntPtr lpInBuffer,
   uint nInBufferSize,
   IntPtr lpOutBuffer,
   uint nOutBufferSize,
   out uint lpBytesReturned,
   IntPtr lpOverlapped);

When thing are generic it’s good, however this one is, probably, most generic method in Win32 API. You can do anything with this method and you never know what to expect in lpOutBuffer :)

However, as I told earlier, I invested three days in investigations and researches (tnx to DDK documentation team) and now things become to be clearer. We need to get CDROM_TOC. It done by invoking IOCTL_CDROM_READ_TOC call

uint bytesRead = 0;
TOC = new Native.CDROM_TOC();
TOC.Length = (ushort)Marshal.SizeOf(TOC);
var hTOC = Marshal.AllocHGlobal(TOC.Length);
Marshal.StructureToPtr(TOC, hTOC, true);
if (Native.DeviceIoControl(this.handle, Native.IOCTL.CDROM_READ_TOC, IntPtr.Zero, 0, hTOC, TOC.Length, out bytesRead, IntPtr.Zero)) Marshal.PtrToStructure(hTOC, TOC);

But, not too fast. CDROM_TOC contains array of TRACK_DATA with unknown size.

typedef struct _CDROM_TOC {
  UCHAR  Length[2];
  UCHAR  FirstTrack;
  UCHAR  LastTrack;
typedef struct _TRACK_DATA {
  UCHAR  Reserved;
  UCHAR  Control : 4;
  UCHAR  Adr : 4;
  UCHAR  TrackNumber;
  UCHAR  Reserved1;
  UCHAR  Address[4];

P/Invoke it! But how to marshal unknown array? We should create wrapper object. Also there is very fun BitVector, used in this structure! What’s the problem? Pin it with some Math!

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

public class CDROM_TOC {

   public ushort Length;

   public byte FirstTrack;

   public byte LastTrack;

   public TRACK_DATA_ARRAY TrackData;


[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

public struct TRACK_DATA {

   public byte Reserved;

   public byte bitVector;

   public byte Control {

      get { return ((byte)((this.bitVector & 15u))); }

      set { this.bitVector = ((byte)((value | this.bitVector))); }


   public byte Adr {

      get { return ((byte)(((this.bitVector & 240u) / 16))); }

      set { this.bitVector = ((byte)(((value * 16) | this.bitVector))); }


   public byte TrackNumber;

   public byte Reserved1;

   public uint Address;


[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

internal sealed class TRACK_DATA_ARRAY {

   internal TRACK_DATA_ARRAY() { data = new byte[MAXIMUM_NUMBER_TRACKS * Marshal.SizeOf(typeof(TRACK_DATA))]; }

   [MarshalAs(UnmanagedType.ByValArray, SizeConst = MAXIMUM_NUMBER_TRACKS * 8)]

   private byte[] data;

   public TRACK_DATA this[int idx] {

      get {

         if ((idx < 0) | (idx >= MAXIMUM_NUMBER_TRACKS)) throw new IndexOutOfRangeException();

         TRACK_DATA res;

         var hData = GCHandle.Alloc(data, GCHandleType.Pinned);

         try {

            var buffer = hData.AddrOfPinnedObject();

            buffer = (IntPtr)(buffer.ToInt32() + (idx * Marshal.SizeOf(typeof(TRACK_DATA))));

            res = (TRACK_DATA)Marshal.PtrToStructure(buffer, typeof(TRACK_DATA));

         } finally {



         return res;




Fuf, done. The code is rather self explaining, we just “tell” marshaler, that we have byte array, while calculating pointers to pinned object to get actual value and marshal it back. So, now we have TOC. So, we know how many tracks we have and addresses to data chunks inside the CD.

But it now enough to understand where our tracks. CD-ROM structure is very tricky. There we have blocks or sectors (which is the smallest chunks of data), so we have to convert bytes into sector addresses. Each block is 2352 bytes in RAW mode, while address value inside TRACK_DATA points us to layout address with is sync, sector id, error detection etc… So, in order to convert TRACK object into actual track number on disk, we have to stick to following method

public static int SectorAddress(this TRACK_DATA data) {

   var addr = BitConverter.GetBytes(data.Address);

   return (addr[1] * 60 * 75 + addr[2] * 75 + addr[3]) – 150;


Now, when we know numbers of tracks, we also know start and end sector, disk type and other useful information we are ready to twist it a bit and read CD-Text (if there are and your CD reader supports it).

So, coming back to our favorite method DeviceIoControl, but this time with IOCTL_CDROM_READ_TOC_EX control.

bytesRead = 0;           
TOCex = new Native.CDROM_READ_TOC_EX {



var sTOCex = Marshal.SizeOf(TOCex);

var hTOCex = Marshal.AllocHGlobal(sTOCex);

Marshal.StructureToPtr(TOCex, hTOCex, true);

var Data = new Native.CDROM_TOC_CD_TEXT_DATA();

Data.Length = (ushort)Marshal.SizeOf(Data);

var hData = Marshal.AllocHGlobal(Data.Length);

Marshal.StructureToPtr(Data, hData, true);

if (Native.DeviceIoControl(this.handle, Native.IOCTL.CDROM_READ_TOC_EX, hTOCex, (ushort)sTOCex, hData, Data.Length, out bytesRead, IntPtr.Zero)) Marshal.PtrToStructure(hData, Data);



Looks too simple? Let’s see inside CDROM_READ_TOC_EX structure. It is very similar to _CDROM_TOC.

typedef struct _CDROM_READ_TOC_EX {
  UCHAR Format : 4;
  UCHAR Reserved1 : 3;
  UCHAR Msf : 1;
  UCHAR SessionTrack;
  UCHAR Reserved2;
  UCHAR Reserved3;

Simple. Isn’t it?

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

public struct CDROM_READ_TOC_EX {

   public uint bitVector;

   public CDROM_READ_TOC_EX_FORMAT Format {

      get { return ((CDROM_READ_TOC_EX_FORMAT)((this.bitVector & 15u))); }

      set { this.bitVector = (uint)((byte)value | this.bitVector); }


   public uint Reserved1 {

      get { return ((uint)(((this.bitVector & 112u) / 16))); }

      set { this.bitVector = ((uint)(((value * 16) | this.bitVector))); }


   public uint Msf {

      get { return ((uint)(((this.bitVector & 128u) / 128))); }

      set { this.bitVector = ((uint)(((value * 128) | this.bitVector))); }


   public byte SessionTrack;

   public byte Reserved2;

   public byte Reserved3;


But what will come inside lpOutBuffer? Fellow structure, named CDROM_TOC_CD_TEXT_DATA with unknown size array of CDROM_TOC_CD_TEXT_DATA_BLOCK

typedef struct _CDROM_TOC_CD_TEXT_DATA {
  UCHAR  Length[2];
  UCHAR  Reserved1;
  UCHAR  Reserved2;
typedef struct _CDROM_TOC_CD_TEXT_DATA_BLOCK {
  UCHAR  PackType;
  UCHAR  TrackNumber:7;
  UCHAR  ExtensionFlag:1;
  UCHAR  SequenceNumber;
  UCHAR  CharacterPosition:4;
  UCHAR  BlockNumber:3;
  UCHAR  Unicode:1;
  union {
    UCHAR  Text[12];
    WCHAR  WText[6];
  UCHAR  CRC[2];

Too bad to be true. Isn’t it? Let’s try to marshal it my hands (with the trick used for TRACK_DATA

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

public class CDROM_TOC_CD_TEXT_DATA {

   public ushort Length;

   public byte Reserved1;

   public byte Reserved2;



[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

internal sealed class CDROM_TOC_CD_TEXT_DATA_BLOCK_ARRAY {


   [MarshalAs(UnmanagedType.ByValArray, SizeConst = MINIMUM_CDROM_READ_TOC_EX_SIZE * MAXIMUM_NUMBER_TRACKS * 18)]

   private byte[] data;

   public CDROM_TOC_CD_TEXT_DATA_BLOCK this[int idx] {

      get {

         if ((idx < 0) | (idx >= MINIMUM_CDROM_READ_TOC_EX_SIZE * MAXIMUM_NUMBER_TRACKS)) throw new IndexOutOfRangeException();


         var hData = GCHandle.Alloc(data, GCHandleType.Pinned);

         try {

            var buffer = hData.AddrOfPinnedObject();

            buffer = (IntPtr)(buffer.ToInt32() + (idx * Marshal.SizeOf(typeof(CDROM_TOC_CD_TEXT_DATA_BLOCK))));

            res = (CDROM_TOC_CD_TEXT_DATA_BLOCK)Marshal.PtrToStructure(buffer, typeof(CDROM_TOC_CD_TEXT_DATA_BLOCK));

         } finally {



         return res;




[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]


   public CDROM_CD_TEXT_PACK PackType;

   public byte bitVector1;

   public byte TrackNumber {

      get { return ((byte)((this.bitVector1 & 127u))); }

      set { this.bitVector1 = ((byte)((value | this.bitVector1))); }


   public byte ExtensionFlag {

      get { return ((byte)(((this.bitVector1 & 128u) / 128))); }

      set { this.bitVector1 = ((byte)(((value * 128) | this.bitVector1))); }


   public byte SequenceNumber;

   public byte bitVector2;        

   public byte CharacterPosition {

      get { return ((byte)((this.bitVector2 & 15u))); }

      set { this.bitVector2 = ((byte)((value | this.bitVector2))); }


   public byte BlockNumber {

      get { return ((byte)(((this.bitVector2 & 112u) / 16))); }

      set { this.bitVector2 = ((byte)(((value * 16) | this.bitVector2))); }


   public byte Unicode {

      get { return ((byte)(((this.bitVector2 & 128u) / 128))); }

      set { this.bitVector2 = ((byte)(((value * 128) | this.bitVector2))); }


   [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12, ArraySubType = UnmanagedType.I1)]

   public byte[] TextBuffer;

   public string Text {

      get { return (Unicode == 1) ? ASCIIEncoding.ASCII.GetString(TextBuffer) : UTF32Encoding.UTF8.GetString(TextBuffer); }


   public ushort CRC;


Can’t you see a small problem here? Yes, we do not know the actual/maximum size of CDROM_TOC_CD_TEXT_DATA_BLOCK array. Until, I’ll find a nice way to marshal smart pointers, we’ll stick to MAX_TRACKS (100) * MIN_DATA_BLOCK (2).

We almost finished and the worst things are behind us. Now you should enumerate thru CDROM_TOC_CD_TEXT_DATA_BLOCK and look for Text, TrackNumber and SequenceNumber (which is continuation of text reported). For example, slot for ALBUM_NAME “Satisfaction” will looks as following

BlockNumber 0×00
CharacterPosition 0×00
SequenceNumber 0×00
BlockNumber 0×00
CharacterPosition 0x0B
CRC 0×0564
SequenceNumber 0×01
Text N


And so on… What to do with all other data and how to use it to enhance listening (ripping/crunching/seeking) experience we’ll speak next time. Have a good day and be good people.

Capturing and streaming sound by using DirectSound with C#

I already wrote a little about managed way to use DirectX DirectSound. Today we’ll speak about how to get sound from your microphone or any other DirectSound capturing device (such as FM receiver) and stream it out to your PC speakers and any other DirectSound Output device. So, let’s start creating our first echo service by using managed DirectX.


First of all we should decide what Wave format we want to use for capturing and recording. So, let’s choose anything reasonable :)

var format = new WaveFormat {
            SamplesPerSecond = 96000,
            BitsPerSample = 16,
            Channels = 2,
            FormatTag = WaveFormatTag.Pcm

Now, we should calculate block align and average byte per second value for this format. I’m wondering why it cannot be done automatically…

format.BlockAlign = (short)(format.Channels * (format.BitsPerSample / 8));
format.AverageBytesPerSecond = format.SamplesPerSecond * format.BlockAlign;

Next step is to set the size of two buffers – one for input and other for output. Generally those buffers are circular, and capturing one should be twice bigger, then output. Why? Because we choose two channels to use. Also, we should decide about chunk size of the buffer, we want to signal when filled.

_dwNotifySize = Math.Max(4096, format.AverageBytesPerSecond / 8);
_dwNotifySize -= _dwNotifySize % format.BlockAlign;
_dwCaptureBufferSize = NUM_BUFFERS * _dwNotifySize;
_dwOutputBufferSize = NUM_BUFFERS * _dwNotifySize / 2;

Next step is to create CaptureBufferDescriptor and actual capturing buffer. We’ll enumerate all devices and choose one, satisfies given string (captureDescriptor) – for example “Mic” :)

var cap = default(Capture);
var cdc = new CaptureDevicesCollection();
for (int i = 0; i < cdc.Count; i++) {
   if (cdc[i].Description.ToLower().Contains(captureDescriptor.ToLower())) {
      cap = new Capture(cdc[i].DriverGuid);
var capDesc = new CaptureBufferDescription {
   Format = format,
   BufferBytes = _dwCaptureBufferSize
_dwCapBuffer = new CaptureBuffer(capDesc, cap);

Then we’ll create output device and buffer. To simplify program, we will use default speakers to output, however, you can choose output device the same way we did for capturing. Also, because DirectSound uses any window as it’s message pump, we have to use SetCooperativeLevel method. In my case (windowless application), I’ll use desktop window as message broker. This why you will have to add Windows.Forms as reference for your project, even if it console application. Also, do not forget to set GlobalFocus value to True, if you want to play echo, even if desktop window is not focused.

var dev = new Device();
dev.SetCooperativeLevel(Native.GetDesktopWindow(), CooperativeLevel.Priority);

var devDesc = new BufferDescription {
   BufferBytes = _dwOutputBufferSize,
   Format = format,
   DeferLocation = true,
   GlobalFocus = true
_dwDevBuffer = new SecondaryBuffer(devDesc, dev);

Now, we will subscribe to buffer notifications and set autoResetEvent to be fired when it filled up.

var _resetEvent = new AutoResetEvent(false);
var _notify = new Notify(_dwCapBuffer);
var bpn1 = new BufferPositionNotify();
bpn1.Offset = _dwCapBuffer.Caps.BufferBytes / 2 – 1;
bpn1.EventNotifyHandle = _resetEvent.SafeWaitHandle.DangerousGetHandle();
var bpn2 = new BufferPositionNotify();
bpn2.Offset = _dwCapBuffer.Caps.BufferBytes – 1;
bpn2.EventNotifyHandle = _resetEvent.SafeWaitHandle.DangerousGetHandle();

_notify.SetNotificationPositions(new BufferPositionNotify[] { bpn1, bpn2 });

Almost done, the only thing we should do is to fire worker thread to take care on messages

int offset = 0;
_dwCaptureThread = new Thread((ThreadStart)delegate {

   while (IsReady) {
      var read = _dwCapBuffer.Read(offset, typeof(byte), LockFlag.None, _dwOutputBufferSize);
      _dwDevBuffer.Write(0, read, LockFlag.EntireBuffer);
      offset = (offset + _dwOutputBufferSize) % _dwCaptureBufferSize;
      _dwDevBuffer.Play(0, BufferPlayFlags.Default);

That’s it. Compile and run. Now if you’ll speak, you can hear your echo from PC speakers.

Merry Christmas for whom concerns and be good people – do not scare your co-workers with strange sounds – be polite and make the volume lower :)

Creating transparent buttons, panels and other control with Compact Framework and putting one into other

In WPF/Silverlight world it’s very simple to make transparent controls and put anything inside anything. However, that’s not the situation in WinForms, and even worth in the world of compact devices with CF. Within this worlds, there is only one way to make controls transparent – to use color masks. Today, we’ll create transparent controls with Compact Framework and put it into panel, which has image background.


So let’s start. First of all, we need create our own control. For this purpose, we have to inherit from Control and override couple of things. More precise: OnPaint and OnPaintBackground. We do not want to paint background for transparent control, so let’s prevent it.

public class TransparentImageButton : Control

protected override void OnPaintBackground(PaintEventArgs e) {

       protected override void OnPaint(PaintEventArgs e) {

Next, we have to get graphics, delivered by OnPain event argument and draw our image over it. However, BitBlt (which is used by core graphics system) is not very fast method, so it’s better for us to draw everything first and then copy final image to the device.

Graphics gxOff;
Rectangle imgRect;
var image = (_isPressed && PressedImage != null) ? PressedImage : Image;

if (_imgOffscreen == null) {
_imgOffscreen = new Bitmap(ClientSize.Width, ClientSize.Height);

gxOff = Graphics.FromImage(_imgOffscreen);


if (image != null) {
var imageLeft = (this.Width – image.Width) / 2;
var imageTop = (this.Height – image.Height) / 2;

if (!_isPressed) imgRect = new Rectangle(imageLeft, imageTop, image.Width, image.Height);
else imgRect = new Rectangle(imageLeft + 1, imageTop + 1, image.Width, image.Height);
var imageAttr = new ImageAttributes();

To make images transparent, we have to use (as mentioned earlier) transparency color key (to tell windows what color it should not draw. We can code or provide this value to detect it by hitting any pixel on the image. Just like this:

public static Color BackgroundImageColor(this Bitmap bmp) {
           return bmp.GetPixel(0, 0);

Now we can keep working.

imageAttr.SetColorKey(image.BackgroundImageColor(), image.BackgroundImageColor());
gxOff.DrawImage(image, imgRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, imageAttr);
} if (_isPressed) {
var rc = this.ClientRectangle;
  gxOff.DrawRectangle(new Pen(Color.Black), rc);
e.Graphics.DrawImage(_imgOffscreen, 0, 0);

Also, we have to provide others with possibility to handle this even too, thus we will not forget to add base.OnPaint(e); at  the end.

Next step is to detect whether our button is clicked or not. We’ll override keyboard and mouse events to detect this.

protected override void OnKeyDown(KeyEventArgs e) {
            _isPressed = this.Focused; this.Invalidate();

        protected override void OnKeyUp(KeyEventArgs e) {
            _isPressed = false; this.Invalidate();

        protected override void OnMouseDown(MouseEventArgs e) {
            _isPressed = this.Focused; this.Invalidate();

        protected override void OnMouseUp(MouseEventArgs e) {
            _isPressed = false; this.Invalidate();

Compile and run to see no problem, when our transparent button lies on solid color control, however, we want to put it into panel with background – just like this one. In this case, you can use real transparent PNG and GIF images, also you can replace transparent color with well known Magenta (or any other color).

public class ImagePanel : Panel {

        public Bitmap Image { get; set; }

        protected override void OnPaintBackground(PaintEventArgs e) {
            e.Graphics.DrawImage(Image, 0, 0);

When we’ll put it onto anything, that has no background color, we’ll see that our “fake transparency” disappears. Why this happen? To provide transparency Windows uses color masks, also while confederating facts, clipping algorithm within GDI is not very trustful, thus the only thing can be taken into account is color. But what to do if we have an image? We should clip it manually. We cannot just get the handle to parent device surface (see above about trustful GDI), so the only way to do it is by providing something, that we know for sure. For example interface, telling us, that parent has image, which drawn on the screen.

internal interface IHaveImage {
        Bitmap Image { get; set; }

When we know it, all we have to do is to clip the region of this image (not device context) and draw it as part of our really transparent control.

if (this.Parent is IHaveImage) {
                var par = this.Parent as IHaveImage;
                gxOff.DrawImage(par.Image.Clip(this.Bounds), 0, 0);

The implementation of Image.Clip is very straight forward.

public static Bitmap GetSS(this Graphics grx, Rectangle bounds) {
    var res = new Bitmap(bounds.Width, bounds.Height);
    var gxc = Graphics.FromImage(res);
    IntPtr hdc = grx.GetHdc();
    PlatformAPI.BitBlt(gxc.GetHdc(), 0, 0, bounds.Width, bounds.Height, hdc, bounds.Left, bounds.Top, PlatformAPI.SRCCOPY);
    return res;

public static Bitmap Clip(this Bitmap source, Rectangle bounds) {
    var grx = Graphics.FromImage(source);
    return grx.GetSS(bounds);

We done. Compiling all together will fake transparency for controls, even when it’s parents background is not pained with  solid color brush.

Source code for this article

P.S. Do not even try to inherit your custom Button control from framework Button class, dev team “forgot” to expose it’s event for override. So, OnPaint, OnPaintBackground, OnKeyUp, OnKeydown, OnMouseUp and OnMouseDown aside with most of other base events will not work for you, also BaseButton class has no default constructor, so the only class you can inherit from is Control.

Have a nice day and be good people.





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