Capture Windows Desktop Image

WinSnap_delphi_snapshot_screen_capture

Or, commonly called screen capture. In Delphi, in order not to degrade the quality of image capture/snapshot, TBitmap typed data usually used to hold the result. It can be converted later to other image formats as desired.

Starting from the Win32 API, each window in Windows has its own handle, an integer of type DWORD (4 bytes). Desktop also is a window. If we know the handle of a window, we can obtain its device context (DC) in the form of a  another handle of type HDC (Handle of Device Context). From the DC handle, we can copy the content of the DC to the Bitmap.

function TFMain.SnapDesktop: TBitmap;
var
DC: TCanvas;
HDesk: THandle;
HCanvas: HDC;
w, h: integer;
begin
HDesk := GetDesktopWindow;
RefreshDesktop;
DC:= TCanvas.Create;
Result := TBitmap.Create;
try
dc.Handle := GetWindowDC(hdesk);
w := Screen.Width;
h := Screen.Height;
Result.Width := w;
Result.Height := h;
BitBlt(Result.Canvas.Handle, 0,0,w, h, dc.Handle, 0, 0, SRCCOPY);
finally
DC.Free;
end;
end;

• GetDesktopWindow () to retrieve the Windows desktop handle.
• GetWindowDC (handleWindow) to retrieve the device context handle, in this case the Windows desktop.
• BitBlt () to copy the content of a device context (DC) to another device context. In the above example, copying from desktop DC to Bitmap DC.

SnapDesktop function above returns an instance of the TBitmap which can then be displayed to the TImage, or saved as an image file, or converted to other image formats. In this example, the Bitmap image will be converted to JPG (TJPEGImage) with the following code:

jpg :=  TJPEGImage.Create;
try
jpg.Assign(VariabelBitmap);
jpg.SaveToFile(NamaFile);
finally
jpg.Free;
end;

In the example code available for download, also available afunction to crop the image so only certain parts are taken into the snapshot.

The following pictures are screenshots of the sample application:

Download

Downloa WinSnap:

WinSnap Binary – 730KB
WinSnap Binary (7Zipped) – 280KB
WinSnap Source (7Zipped) – 20KB

UPDATE:

WinSnap Binary + Source (7Zipped) – 300KB. Added new functionality, to snap selected window only.

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