Webcam Web Service

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Contents

• Introduction
• Web Service
• Client
• Conclusion
• Faced Problems

Introduction

C# Webcam is a port to ASP.NET and C# of the C++ ATL Web Service. It demonstrates the ease of use of C# and ASP.NET to build Web Services compared to ATL Server Web Service.

The project is still based on the Webcam COM component developed in the C++ ATL Web Service. .NET COM Interop is used to import it in the C# project.

Web Service

With Visual Studio, create a new C# ASP.NET Web Service project. Add a reference to 'CamServer 1.0 Type Library' on the COM tab. If 'CamServer 1.0 Type Library' is not in the list, you need to register the Dll CamServer.dll in the 'COM Components' directory. Add this Web Method to the source code obtained by the wizard:

[WebMethod]
public byte[] GrabFrame( short nQuality )
{
    //Shoot a picture from my webcam

    CAMSERVERLib.Camera cam = new CAMSERVERLib.CameraClass();

    return (byte[])cam.GrabFrame( nQuality );
}

Compared to the C++ ATL Web Service we need only three lines of code to get the picture from the COM component and return it to the client.

To have a little more fun coding I decided to add some features. Now it writes to the Windows EventLog the IP and the name of the machine calling it, after a DNS resolution. I have also added the date and hour of the local computer directly in the picture. And at last it increments a system performance counter to keep an eye on the number of people calling it.

[WebMethod]
public byte[] GrabFrame( short nQuality )
{
    //Write to the EventLog the IP and Host name

    string addr = HttpContext.Current.Request.UserHostAddress.Trim();

    string name;

    IPHostEntry host = null;

    try
    {
        host = System.Net.Dns.GetHostByAddress( addr );

        if ( host != null )
        {
            name = host.HostName;
            for( int i = 0; i < host.Aliases.Length; i++ )
                name += "*" + host.Aliases[i];

            eventLog.WriteEntry( addr + " : " + name );
        }
        else
        {
            name = "ERROR";

            eventLog.WriteEntry( name );
        }
    }
    catch( System.Exception error )
    {
        // process the error error.Message

    }

    //Shoot a picture from my webcam

    CAMSERVERLib.Camera cam = new CAMSERVERLib.CameraClass();

    byte[] picture = (byte[])cam.GrabFrame( nQuality );

    //Increments Performance Counter

    performanceCounterShoot.Increment();

    //Add the hour

    MemoryStream ms = new MemoryStream( picture );
    Bitmap bmp = new Bitmap( ms );

    Graphics g = Graphics.FromImage( bmp );

    string strDate = DateTime.Now.ToLongDateString() + 
                     " - " + 
                     DateTime.Now.ToLongTimeString(); 

    g.DrawString(   strDate,
                    new Font( FontFamily.GenericSansSerif, 10 ),
                    new SolidBrush( Color.Black ), 
                    new RectangleF( 1,1,320,240 ) 
                );

    g.DrawString(   strDate,
                    new Font( FontFamily.GenericSansSerif, 10 ),
                    new SolidBrush( Color.White ), 
                    new RectangleF( 0,0,320,240 ) 
                );

    MemoryStream ms2 = new MemoryStream();

    //Get codecs

    ImageCodecInfo[] icf = ImageCodecInfo.GetImageEncoders();

    EncoderParameters encps = new EncoderParameters( 1 );
    EncoderParameter encp = new EncoderParameter( Encoder.Quality, (long) nQuality );

    //Set quality

    encps.Param[0] = encp;

    bmp.Save( ms2, icf[1], encps );
    ms2.Close();

    return ms2.ToArray();
}

Client

The client ActiveX has no need to be modified. It is just needed to change the url of the Web Service, that is now:
http://YOUR_IP/webcamcsharp/service1.asmx?WSDL

Don't forget to register with regsvr32.exe the AxCamClient.dll in the 'COM Components' directory.

Conclusion

With few lines of source code you may obtain the same result then with little more C++ work.

The solution may be better because the COM component pack the picture, we unpack it to add date and hour then we pack again the new picture to send back to the client.

Problems Faced 

• None.

History

Version 1.00

April 10, 2002 First release.