How can I capture screen under my own window excluding my own window

Question

Assuming I would like to program a magnifier, how could I capture the content of the screen excluding my very own window ? I know how to capture the screen with my own windo

Answer 1

During the capture process set the forms AlphaBlend property to true and the AlphaBlendValue to 0. Be aware that this will make your form completely invisible.

Answer 2

You need to capture the screenshot from the DC of the desktop, into a bitmap in memory.

procedure CaptureScreenShot(acapture: TBitMap);
 var c: TCanvas;
     r: TRect;
 begin
  c:= TCanvas.Create;
  c.Handle:= GetWindowDC (GetDesktopWindow);
  try
    r:= Rect(0,0,screen.width,screen.height);
    acapture.Width:=screen.Width;
    acapture.Height:=screen.Height;
    acapture.Canvas.CopyRect(r, c, r);
  finally
    ReleaseDC(0, c.handle);
    c.Free;
  end;
end;

Add to this Uwe's answer to make your form invisible and you have....

FCapturedScreenShot:TBitmap;
....
FCapturedScreenShot:=TBitmap.Create;
....
AlphaBlend:=true;
AlphaBlendValue:=0; 
CaptureScreenshot(FCapturedScreenShot);
AlphaBlendValue:=False; 

use the captured screenshot for whatever you need, you might assign it over a bitmap in another form, or save it in an array of captured screens...

Answer 3

Try to minimize or hide you form before capture the screen and restore or show the form after capture screen

Answer 4

You use PrintWindow() for that, but it is not fast and does not work for all applications.