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:

1. setting pictureBox.Size
2. 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!

Answer 1

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.