Saving a screenshot of a window using C#, WPF, and DWM

Question

This is a follow up question to this question

The solution to the above uses DWM to display a thumbnail of an active window. If I understand correctly, it works by letting you specify the window handle of the application you want to view and then having you provide a window handle and a location on that window where windows should draw the contents of the target Window.

Is there a way to render the window screen shot directly to BitmapImage or Image instead of directly drawing it somewhere in your window? (Basically to just grab a screen shot of the window - even if it's covered by another window - with out using an updating thumbnail.)

Thanks for you help!

Cory Charlton · Answer 1 · 2010-03-12T17:15:05.547

The Control.DrawToBitmap doesn't always work so I resorted to the following native API calls that provide more consistent results:

The Utilities class. Call Utilities.CaptureWindow(Control.Handle) to capture a specific control:

public static class Utilities
{
    public static Image CaptureScreen()
    {
        return CaptureWindow(User32.GetDesktopWindow());
    }

    public static Image CaptureWindow(IntPtr handle)
    {

        IntPtr hdcSrc = User32.GetWindowDC(handle);

        RECT windowRect = new RECT();
        User32.GetWindowRect(handle, ref windowRect);

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

        IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc);
        IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height);

        IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap);
        Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, ApiConstants.SRCCOPY);
        Gdi32.SelectObject(hdcDest, hOld);
        Gdi32.DeleteDC(hdcDest);
        User32.ReleaseDC(handle, hdcSrc);

        Image image = Image.FromHbitmap(hBitmap);
        Gdi32.DeleteObject(hBitmap);

        return image;
    }
}

The Gdi32 class:

public class Gdi32
{
    [DllImport("gdi32.dll")]
    public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hObjectSource, int nXSrc, int nYSrc, int dwRop);
    [DllImport("gdi32.dll")]
    public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth, int nHeight);
    [DllImport("gdi32.dll")]
    public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
    [DllImport("gdi32.dll")]
    public static extern bool DeleteDC(IntPtr hDC);
    [DllImport("gdi32.dll")]
    public static extern bool DeleteObject(IntPtr hObject);
    [DllImport("gdi32.dll")]
    public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
}

The User32 class:

public static class User32
{
    [DllImport("user32.dll")]
    public static extern IntPtr GetDesktopWindow();
    [DllImport("user32.dll")]
    public static extern IntPtr GetWindowDC(IntPtr hWnd);
    [DllImport("user32.dll")]
    public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);
    [DllImport("user32.dll")]
    public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
}

The constants used:

    public const int SRCCOPY = 13369376;

The structs used:

[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
    public int left;
    public int top;
    public int right;
    public int bottom;
}

A friendly Control extension method:

public static class ControlExtensions
{
    public static Image DrawToImage(this Control control)
    {
        return Utilities.CaptureWindow(control.Handle);
    }
}

This was useful, but I've posted a followup question here: http://stackoverflow.com/questions/2322217/getting-window-screenshots-but-text-portions-are-transparent — Josh Santangelo, Feb 23 '10 at 22:33
great, this is a super fast code. But wpf controls does not have a handle :( — Andreas, Nov 16 '11 at 09:28

score 2 · Answer 2 · answered Dec 07 '09 at 09:46

2

Use Control.DrawToBitmap Method

Image img = myForm.DrawToBitmap();
Image img = myPanel.DrawToBitmap();

answered Dec 07 '09 at 09:46

serhio

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Thanks for your reply. Wouldn't this would require the screen shot to be drawn on the screen first and then saved? Is there a way to capture the screen shot of a window directly to an object (like Image) without having to draw it on the screen first? – Evan Dec 07 '09 at 18:23
DrawToBitmap obtains an Bitmap like you do when pressing the PrintScreen Button (on the form or for panel only). I am not sure if the form or panel should or not be really displayed on the screen, with visible panels is surely works, I believe with the hidden should work too. Bitmap bm = new Bitmap(wid, hgt); ' draw the current form to the bitmap this.DrawToBitmap(bm, new Rectangle(0, 0, wid, hgt)) – serhio Dec 08 '09 at 16:40

Saving a screenshot of a window using C#, WPF, and DWM

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