Question

I know I can get the screenshot of the entire screen using Graphics.CopyFromScreen(). However, what if I just want the screenshot of a specific application?

Answer 1

Here’s some code to get you started:

public void CaptureApplication(string procName)
{
    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);
    using (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);
}

It works, but needs improvement:

• You may want to use a different mechanism to get the process handle (or at least do some defensive coding)
• If your target window isn’t in the foreground, you’ll end up with a screenshot that’s the right size/position, but will just be filled with whatever is in the foreground (you probably want to pull the given window into the foreground first)
• You probably want to do something other than just save the bmp to a temp directory