Screenshots of non-top windows

How to intercept non-front-end Forms

First, let's talk about the use of the printwindow API.

Public static bitmap getwindowcapture (intptr hwnd)
{
Intptr hscrdc = getwindowdc (hwnd );
Rect windowrect = new rect ();
Getwindowrect (hwnd, ref windowrect );
Int width = windowrect. Right-windowrect. Left;
Int Height = windowrect. Bottom-windowrect. Top;

Intptr hbitmap = createcompatiblebitmap (hscrdc, width, height );
Intptr hmemdc = createcompatibledc (hscrdc );
SelectObject (hmemdc, hbitmap );
Printwindow (hwnd, hmemdc, 0 );
Bitmap BMP = bitmap. fromhbitmap (hbitmap );
Deletedc (hscrdc); // deletes a used object.
Deletedc (hmemdc); // delete an object that has been used
Return BMP;
}

[Dllimport ("user32.dll")]
Public static extern intptr getwindowrect (intptr hwnd, ref rect );

[Dllimport ("gdi32.dll")]
Public static extern intptr createdc (
String lpszdriver, // driver name
String lpszdevice, // device name
String lpszoutput, // not used; shocould be null
Intptr lpinitdata // optional printer data
);
[Dllimport ("gdi32.dll")]
Public static extern int bitblt (
Intptr hdcdest, // handle of the target device to destination DC
Int nxdest, // X-coord of destination upper-left corner X coordinate in the upper left corner of the target object
Int nydest, // y-coord of destination upper-left corner y coordinate in the upper left corner of the target object
Int nwidth, // width of destination rectangle the width of the rectangle of the target object
Int nheight, // height of destination rectangle specifies the length of the rectangle of the target object.
Intptr hdcsrc, // handle to source DC Source Device
Int nxsrc, // X-coordinate of source upper-left corner X coordinate in the upper left corner of the source object
Int nysrc, // y-coordinate of source upper-left corner y coordinate in the upper left corner of the source object
Uint32 dwrop // operation value of raster operation code Grating
);

[Dllimport ("gdi32.dll")]
Public static extern intptr createcompatibledc (
Intptr HDC // handle to DC
);

[Dllimport ("gdi32.dll")]
Public static extern intptr createcompatiblebitmap (
Intptr HDC, // handle to DC
Int nwidth, // width of bitmap, in pixels
Int nheight // height of bitmap, in pixels
);

[Dllimport ("gdi32.dll")]
Public static extern intptr SelectObject (
Intptr HDC, // handle to DC
Intptr hgdiobj // handle to object
);

[Dllimport ("gdi32.dll")]
Public static extern int deletedc (
Intptr HDC // handle to DC
);

[Dllimport ("user32.dll")]
Public static extern bool printwindow (
Intptr hwnd, // window to copy, handle to the window that will be copied.
Intptr hdcblt, // HDC to print into, handle to the device context.
Uint32 nflags // optional flags, specifies the drawing options. It can be one of the following values.
);

[Dllimport ("user32.dll")]
Public static extern intptr getwindowdc (
Intptr hwnd
);

 

 

Unfortunately, the above can indeed intercept non-front-end forms, but non-GDI programs cannot, such as DirectX

The following describes the use of bitblt APIs.

 

/// <Summary>
/// Provides full screen and specified Windows and classes for saving as files
/// </Summary>
Public class screencapture
{
/// <Summary>
/// Full screen
/// </Summary>
/// <Returns> </returns>
Public Image capturescreen ()
{
Return capturewindow (user32.getdesktopwindow ());
}
/// <Summary>
/// Specify the window
/// </Summary>
/// <Param name = "handle"> window handle. (obtained from the handle attribute in a Windows Application) </param>
/// <Returns> </returns>
Public Image capturewindow (intptr handle)
{
Intptr hdcsrc = user32.getwindowdc (handle );
User32.rect windowrect = new user32.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, gdi32.srccopy );
Gdi32.selectobject (hdcdest, hold );
Gdi32.deletedc (hdcdest );
User32.releasedc (handle, hdcsrc );
Image IMG = image. fromhbitmap (hbitmap );
Gdi32.deleteobject (hbitmap );
Return IMG;
}
/// <Summary>
/// Specify the window to save as an image 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>
/// Save as a file in full screen
/// </Summary>
/// <Param name = "FILENAME"> </param>
/// <Param name = "format"> </param>
Public void capturescreentofile (string filename, imageformat format)
{
Image IMG = capturescreen ();
IMG. Save (filename, format );
}

/// <Summary>
/// The helper class defines the GDI32 API Function
/// </Summary>
Private class GDI32
{

Public const int srccopy = 0x00cc0020;
[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>
/// The auxiliary class defines the USER32 API Function
/// </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 getasktopwindow ();
[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 );
}
}

 

 

The above class uses the bitblt API to intercept GDI or non-GDI graphics, but non-front-end form graphics cannot intercept...

The following describes the simplest full screen solution without using APIs.

 

Public static bitmap copyprimaryscreen ()
{
Screen S = screen. primaryscreen;
Rectangle r = S. bounds;
Int W = R. width;
Int H = R. height;
Bitmap BMP = new Bitmap (W, H );
Graphics G = graphics. fromimage (BMP );
G. copyfromscreen
(
New Point (0, 0 ),
New Point (0, 0 ),
New size (W, H)
);
Return BMP;
}

 

Finally, try the following method:

 

As long as the visable of the form is true, a graph can be captured even outside the screen. If it is false, it is a black image, hehe.
 
Public static bitmap getwindow (intptr hwnd)
{
Intptr hscrdc = getwindowdc (hwnd );
Control control = control. fromhandle (hwnd );
Intptr hbitmap = createcompatiblebitmap (hscrdc, Control. Width, Control. Height );
Intptr hmemdc = createcompatibledc (hscrdc );
SelectObject (hmemdc, hbitmap );
Printwindow (hwnd, hmemdc, 0 );
Bitmap BMP = bitmap. fromhbitmap (hbitmap );
Deletedc (hscrdc); // deletes a used object.
Deletedc (hmemdc); // delete an object that has been used
Return BMP;
}

API Declaration

[Dllimport ("gdi32.dll")]
Public static extern intptr createdc (
String lpszdriver, // driver name
String lpszdevice, // device name
String lpszoutput, // not used; shocould be null
Intptr lpinitdata // optional printer data
);
[Dllimport ("gdi32.dll")]
Public static extern int bitblt (
Intptr hdcdest, // handle of the target device to destination DC
Int nxdest, // X-coord of destination upper-left corner X coordinate in the upper left corner of the target object
Int nydest, // y-coord of destination upper-left corner y coordinate in the upper left corner of the target object
Int nwidth, // width of destination rectangle the width of the rectangle of the target object
Int nheight, // height of destination rectangle specifies the length of the rectangle of the target object.
Intptr hdcsrc, // handle to source DC Source Device
Int nxsrc, // X-coordinate of source upper-left corner X coordinate in the upper left corner of the source object
Int nysrc, // y-coordinate of source upper-left corner y coordinate in the upper left corner of the source object
Uint32 dwrop // operation value of raster operation code Grating
);

[Dllimport ("gdi32.dll")]
Public static extern intptr createcompatibledc (
Intptr HDC // handle to DC
);

[Dllimport ("gdi32.dll")]
Public static extern intptr createcompatiblebitmap (
Intptr HDC, // handle to DC
Int nwidth, // width of bitmap, in pixels
Int nheight // height of bitmap, in pixels
);

[Dllimport ("gdi32.dll")]
Public static extern intptr SelectObject (
Intptr HDC, // handle to DC
Intptr hgdiobj // handle to object
);

[Dllimport ("gdi32.dll")]
Public static extern int deletedc (
Intptr HDC // handle to DC
);

[Dllimport ("user32.dll")]
Public static extern bool printwindow (
Intptr hwnd, // window to copy, handle to the window that will be copied.
Intptr hdcblt, // HDC to print into, handle to the device context.
Uint32 nflags // optional flags, specifies the drawing options. It can be one of the following values.
);

[Dllimport ("user32.dll")]
Public static extern intptr getwindowdc (
Intptr hwnd
);