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Raúl

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Posts: 591

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Simulated WebCam exception in QueryFrame - 2007/09/18 12:31 I found a bug in the Robotics Studio SimulatedWebcam service.

The problem is that after a few seconds (some times it takes longer) I get an InvalidOperationException in the QueryFrameHandler method in file SimulatedWebcam.cs (The lines causing the exception are these:

Code:


 // size not specified
if(size.Width == 0)
  size = _state.Image.Size;

see the rest of the code below)

The runtime is complaining because Object (_state.Image) is currently in use elsewhere.

I think the size assignment should be moved within the next try-catch. Also the method QueryFrameHandler should declared as Exclusive, because the image is being locked in the method.

Microsoft are making these changes for the next release.

Code:


 [ServiceHandler(ServiceHandlerBehavior.Concurrent)]

public IEnumerator<ITask> QueryFrameHandler(webcam.QueryFrame query)

{

if (_state.Image == null)
{
query.ResponsePort.Post(new webcam.QueryFrameResponse());
yield break;
}

Size size = new Size((int)query.Body.Size.X, (int)query.Body.Size.Y);

if (query.Body.Format == Guid.Empty)
{

// raw image requested;
BitmapData raw = null;

 // size not specified
if(size.Width == 0)
  size = _state.Image.Size;

try
{
raw = _state.Image.LockBits(new Rectangle(Point.Empty, size),
ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
int byteSize = raw.Height * raw.Stride;
webcam.QueryFrameResponse response = new webcam.QueryFrameResponse();

response.TimeStamp = _state.LastFrameUpdate;
response.Frame = new byte[byteSize];
response.Size = new Size(raw.Width, raw.Height);
response.Format = Guid.Empty;
System.Runtime.InteropServices.Marshal.Copy(raw.Scan0, response.Frame, 0, byteSize);
query.ResponsePort.Post(response);
}

catch (Exception ex)
{
query.ResponsePort.Post(Fault.FromException(ex));
}

finally
{
if (raw != null)
{

_state.Image.UnlockBits(raw);

}
}
}

else
{

ImageFormat format = new ImageFormat(query.Body.Format);
using (MemoryStream stream = new MemoryStream())
{ 
if (size == _state.Image.Size ||
size.Width == 0 ||
size.Height == 0 ||
size.Width >= _state.Image.Width ||
size.Height >= _state.Image.Height)
{
size = _state.Image.Size;
_state.Image.Save(stream, format);
}
else
{
using (Bitmap temp = new Bitmap(
_state.Image, size))
{
temp.Save(stream, format);
}
}

webcam.QueryFrameResponse response = new webcam.QueryFrameResponse();
response.TimeStamp = _state.LastFrameUpdate;
response.Frame = new byte[(int)stream.Length];
response.Size = size;
response.Format = format.Guid;
stream.Position = 0;
stream.Read(response.Frame, 0, response.Frame.Length);
query.ResponsePort.Post(response);
}
}

yield break;
}

Post edited by: Raúl, at: 2007/09/18 12:45 Raúl Arrabales Moreno. conscious-robots.com/raul

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Raúl

Moderator

Posts: 591

Karma: 10

Re:Simulated WebCam exception in QueryFrame - 2007/09/18 13:25 The code after making the mentioned changes is as follows (this code seems to work ok. I am unsure whether or not some frames are loss when the method is called when the simulator engine has blocked the image).

Code:


         // Raul - Service handler changed from Concurrent to Exclusive.
        [ServiceHandler(ServiceHandlerBehavior.Exclusive)]
        public IEnumerator<ITask> QueryFrameHandler(webcam.QueryFrame query)
        {
            if (_state.Image == null)
            {
                query.ResponsePort.Post(new webcam.QueryFrameResponse());
                yield break;
            }

            Size size = new Size((int)query.Body.Size.X, (int)query.Body.Size.Y);

            if (query.Body.Format == Guid.Empty)
            {
                // raw image requested;
                BitmapData raw = null;


                try
                {
                    // Raul - This check moved into the try-catch block.
                    // size not specified
                    if (size.Width == 0)
                        size = _state.Image.Size;

                    raw = _state.Image.LockBits(new Rectangle(Point.Empty, size),
                        ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

                    int byteSize = raw.Height * raw.Stride;

                    webcam.QueryFrameResponse response = new webcam.QueryFrameResponse();

                    response.TimeStamp = _state.LastFrameUpdate;
                    response.Frame = new byte[byteSize];
                    response.Size = new Size(raw.Width, raw.Height);
                    response.Format = Guid.Empty;

                    System.Runtime.InteropServices.Marshal.Copy(raw.Scan0, response.Frame, 0, byteSize);

                    query.ResponsePort.Post(response);
                }
                catch (Exception ex)
                {
                    query.ResponsePort.Post(Fault.FromException(ex));
                }
                finally
                {
                    if (raw != null)
                    {
                        _state.Image.UnlockBits(raw);
                    }
                }
            }
            else
            {
                ImageFormat format = new ImageFormat(query.Body.Format);

                using (MemoryStream stream = new MemoryStream())
                {                    
                    if (size == _state.Image.Size ||
                        size.Width == 0 ||
                        size.Height == 0 ||
                        size.Width >= _state.Image.Width ||
                        size.Height >= _state.Image.Height)
                    {
                        size = _state.Image.Size;
                        _state.Image.Save(stream, format);
                    }
                    else
                    {
                        using (Bitmap temp = new Bitmap(
                            _state.Image, size))
                        {
                            temp.Save(stream, format);
                        }
                    }


                    webcam.QueryFrameResponse response = new webcam.QueryFrameResponse();
                    response.TimeStamp = _state.LastFrameUpdate;
                    response.Frame = new byte[(int)stream.Length];
                    response.Size = size;
                    response.Format = format.Guid;

                    stream.Position = 0;
                    stream.Read(response.Frame, 0, response.Frame.Length);

                    query.ResponsePort.Post(response);
                }
            }
            yield break;
        }

Raúl Arrabales Moreno. conscious-robots.com/raul

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