Taking a screen shot of a window using Delphi code is rather easy.
A screen shot (screen capture) is a copy of the screen's contents that can be saved as a graphics file or displayed in a graphics "aware" control, for example TImage.
In most cases you will want to take a screen shot of the active window or the Windows Desktop.
What if you need to do a screen capture of all the running applications - most of them will be inactive and not visible to the user?
WindowSnap - Inactive Window Screen CaptureWindows XP also introduces the new printing API, PrintWindow. This API enables the caller to snapshot a visual copy of a window into a device context.
Drop a TImage (named "Image1") on a form and use the following code:
The actual WindowSnap function is defined as:
WindowSnap(Self.Handle, Image1.Picture.Bitmap) ; Image1.Refresh;
Note that the first parameter to the WindowSnap procedure is a HWND value (THandle) - the handle of the window you want to capture.
uses Windows; //if not already used function WindowSnap(windowHandle: HWND; bmp: TBitmap): boolean; var r: TRect; user32DLLHandle: THandle; printWindowAPI: function(sourceHandle: HWND; destinationHandle: HDC; nFlags: UINT): BOOL; stdcall; begin result := False; user32DLLHandle := GetModuleHandle(user32) ; if user32DLLHandle <> 0 then begin @printWindowAPI := GetProcAddress(user32DLLHandle, 'PrintWindow') ; if @printWindowAPI <> nil then begin GetWindowRect(windowHandle, r) ; bmp.Width := r.Right - r.Left; bmp.Height := r.Bottom - r.Top; bmp.Canvas.Lock; try result := printWindowAPI(windowHandle, bmp.Canvas.Handle, 0) ; finally bmp.Canvas.Unlock; end; end; end; end; (*WindowSnap*)
WinDowse is an extremely convenient and easy to use tool for obtaining necessary technical information about any window (handle, child windows, etc.)
Here's an idea: enumerate top-level windows (to grab their handles) and create your own task-switcher :)