Can not pass winform control size into unmanaged code

Question

I use unmanaged libraries to obtain video stream from IP Camera. There is function:

[DllImport("client.dll", EntryPoint = "Network_ClientStartLive", SetLastError = true)]
protected static extern int Network_ClientStartLive(
        ref IntPtr pStream,
        IntPtr hDev,
        IntPtr pClientInfo,
        [MarshalAs(UnmanagedType.FunctionPtr)] ReadDatacbf lpfnCallbackFunc = null,
        UInt32 dwUserData = 0
    );

The pClientInfo is a pointer to structure type of:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
protected struct LiveConnect
{
    public UInt32 dwChannel;
    public IntPtr hPlayWnd;
    public UInt32 dwConnectMode;
}

where hPlayWnd is a handle of window in which video stream must be output. The library detects the video resolution by size of this window (during the call to Network_ClientStartLive). I checked it on C++ MFC program, where output window is Picture control and by setting size with method MoveWindow was defined output video resolution.

In the C# version of this program I'm using a PictureBox-control to draw the video stream. The video is displayed but the size of the PictureBox does not affect to video stream resolution. I tried several methods to change PictureBox size:

setting pictureBox.Size
using WinAPI SetWindowPos:

[DllImport("user32.dll")]
private static extern bool SetWindowPos(
    IntPtr hWnd, 
    IntPtr hWndInsertAfter,
    int x, 
    int y, 
    int width, 
    int height, 
    uint uFlags);

In both methods the size of the control was changed but the camera library continued to output video stream in maximum resolution.

How can I solve this problem?

Thanks!

I can't think of a failure mode, there is nothing fundamentally different between a .NET PictureBox and an unmanaged picture control as far as unmanaged code would ever care about or see. Consider the possibility that you are passing the wrong window handle. Like the form's or the desktop's (null). Contact the camera library vendor or author for support, they can easily debug this. — Hans Passant
I also suspect the handle is wrong. Write the handle you're passing to a log and while your app is running, use the Spy++ utility to select the picturebox. If the handle Spy++ doesn't match the handle you logged, you'll know something is up. — dazedandconfused

Caleb Everett Caleb Everett · Accepted Answer · 2013-12-27T14:38:56

Every control in Windows Forms has a SizeChanged (http://msdn.microsoft.com/en-us/library/system.windows.forms.control.sizechanged(v=vs.110).aspx) event. Maybe its possible to add code to change the video resolution manually in this event handler? If not, the PictureBox handle you provide may not be sending WM_SIZE messages which would be what the unmanaged library would be looking for. As mentioned in one of the comments, Spy++ (included with Visual Studio) would be a useful program to monitor the messages and make sure that the handle values and the events are what you expect them to be.

Can not pass winform control size into unmanaged code

1 Answers