Library code snippets
Capture a Screen Shot
By James Crowley, published on 13 Apr 2004
This code demonstrates how to get a screen shot of the entire desktop, or a particular window, using .NET (and a few API functions). The C# version is shown here, but the download includes a VB.NET version too.
Using the class is simple - there are four methods
-
public Image CaptureScreen()Creates an Image object containing a screen shot of the entire desktop -
public Image CaptureWindow(IntPtr handle)Creates an Image object containing a screen shot of a specific window -
public void CaptureWindowToFile(IntPtr handle, string filename, ImageFormat format)Captures a screen shot of a specific window, and saves it to a file -
public void CaptureScreenToFile(string filename, ImageFormat format)Captures a screen shot of the entire desktop, and saves it to a file
A quick demonstration of how to use it...
ScreenCapture sc = new ScreenCapture();
// capture entire screen, and save it to a file
Image img = sc.CaptureScreen();
// display image in a Picture control named imageDisplay
this.imageDisplay.Image = img;
// capture this window, and save it
sc.CaptureWindowToFile(this.Handle,"C:\\temp2.gif",ImageFormat.Gif);
And here's the code to the class we're using
using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;
namespace ScreenShotDemo
{
/// <summary>
/// Provides functions to capture the entire screen, or a particular window, and save it to a file.
/// </summary>
public class ScreenCapture
{
/// <summary>
/// Creates an Image object containing a screen shot of the entire desktop
/// </summary>
/// <returns></returns>
public Image CaptureScreen()
{
return CaptureWindow( User32.GetDesktopWindow() );
}
/// <summary>
/// Creates an Image object containing a screen shot of a specific window
/// </summary>
/// <param name="handle">The handle to the window. (In windows forms, this is obtained by the Handle property)</param>
/// <returns></returns>
public Image CaptureWindow(IntPtr handle)
{
// get te hDC of the target window
IntPtr hdcSrc = User32.GetWindowDC(handle);
// get the size
User32.RECT windowRect = new User32.RECT();
User32.GetWindowRect(handle,ref windowRect);
int width = windowRect.right - windowRect.left;
int height = windowRect.bottom - windowRect.top;
// create a device context we can copy to
IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
// create a bitmap we can copy it to,
// using GetDeviceCaps to get the width/height
IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc,width,height);
// select the bitmap object
IntPtr hOld = GDI32.SelectObject(hdcDest,hBitmap);
// bitblt over
GDI32.BitBlt(hdcDest,0,0,width,height,hdcSrc,0,0,GDI32.SRCCOPY);
// restore selection
GDI32.SelectObject(hdcDest,hOld);
// clean up
GDI32.DeleteDC(hdcDest);
User32.ReleaseDC(handle,hdcSrc);
// get a .NET image object for it
Image img = Image.FromHbitmap(hBitmap);
// free up the Bitmap object
GDI32.DeleteObject(hBitmap);
return img;
}
/// <summary>
/// Captures a screen shot of a specific window, and saves it to a file
/// </summary>
/// <param name="handle"></param>
/// <param name="filename"></param>
/// <param name="format"></param>
public void CaptureWindowToFile(IntPtr handle, string filename, ImageFormat format)
{
Image img = CaptureWindow(handle);
img.Save(filename,format);
}
/// <summary>
/// Captures a screen shot of the entire desktop, and saves it to a file
/// </summary>
/// <param name="filename"></param>
/// <param name="format"></param>
public void CaptureScreenToFile(string filename, ImageFormat format)
{
Image img = CaptureScreen();
img.Save(filename,format);
}
/// <summary>
/// Helper class containing Gdi32 API functions
/// </summary>
private class GDI32
{
public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter
[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);
}
/// <summary>
/// Helper class containing User32 API functions
/// </summary>
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 GetDesktopWindow();
[DllImport("user32.dll")]
public static extern IntPtr GetWindowDC(IntPtr hWnd);
[DllImport("user32.dll")]
public static extern IntPtr ReleaseDC(IntPtr hWnd,IntPtr hDC);
[DllImport("user32.dll")]
public static extern IntPtr GetWindowRect(IntPtr hWnd,ref RECT rect);
}
}
}
James first started this website when learning Visual Basic back in 1999 whilst studying his GCSEs. The site grew steadily over the years while being run as a hobby - to a regular monthly audience ...
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I'd like to congratulate you for the clean code you provided.
I am curious about whether you have seen / can solve an interesting problem I've run into: using the class you provided in a windows forms applicatin, I have implemented a test routine using a timer. This routine saved the screenshot of the screen every 10 seconds and saving it with a randomized / time oriented name. After testing locally and making sure the code worked fine, I have uploaded it to a remote computer and ran it. Worked fine at first, but leaving the application running and closing the remote connection lead into black screenshots.
Actually I have been developing another application that spiders some urls and gathers their screenshots and sends them to some people. It all worked well until deployment. After deployment I realized the problem I tried to explain above.
Is there a way any stand alone .net application can take non-black / non-blank screenshots without the need for an active/logged on user?
Thanks.