Take screenshot in process window

Question

I am trying to make a screenshot to the window of a process in Windows 7 64 bit, the problem is that I always get error in the following line:

var bmp = new Bitmap (width, height, PixelFormat.Format32bppArgb);

Saying "invalid parameters", I made a throw to see the errors and width and height are always 0.

Before in 32 bits it worked well, but now in 64 bits it does not work anymore.

The code :

public void CaptureApplication()
{
    string procName = "firefox";

    var proc = Process.GetProcessesByName(procName)[0];
    var rect = new User32.Rect();
    User32.GetWindowRect(proc.MainWindowHandle, ref rect);

    int width = rect.right - rect.left;
    int height = rect.bottom - rect.top;

    var bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb);
    Graphics graphics = Graphics.FromImage(bmp);
    graphics.CopyFromScreen(rect.left, rect.top, 0, 0, new Size(width, height), CopyPixelOperation.SourceCopy);

    bmp.Save("c:\\tmp\\test.png", ImageFormat.Png);
}

private class User32
{
    [StructLayout(LayoutKind.Sequential)]
    public struct Rect
    {
        public int left;
        public int top;
        public int right;
        public int bottom;
    }

    [DllImport("user32.dll")]
    public static extern IntPtr GetWindowRect(IntPtr hWnd, ref Rect rect);
}

How do I fix this error?

Answer 1

Getting the process of firefox returns an array of processes and you are looking for the one with an rectangle with realistic sizes which is the main process.

Process[] procs = Process.GetProcessesByName(procName);
var rect = new User32.Rect();
int width = 0;
int height = 0:
foreach (Process proc in procs)
{
    User32.GetWindowRect(proc.MainWindowHandle, ref rect);
    width = rect.right - rect.left;
    height = rect.bottom - rect.top;
    // break foreach if an realistic rectangle found => main process found
    if (width != 0 && height != 0)
    {
        break;
    }
}