Author: Jonas Bilinkevicius 

I'd like to draw on the screen, and not necessarily in the application form. 
Example: When the application is running but the form is minimized, I'd like to be 
able to draw a circle on the desktop.

Answer:

1   procedure THovedForm.Tegn1ButtonClick(Sender: TObject);
2   var
3     DesktopDC: HDC;
4     Rectangle: TRect;
5     pcTekst: PChar;
6   begin
7     DesktopDC := GetWindowDC(GetDesktopWindow);
8     MoveToEx(DesktopDC, 0, 0, nil);
9     LineTo(DesktopDC, Screen.Width, Screen.Height);
10    MoveToEx(DesktopDC, 0, Screen.Height, nil);
11    LineTo(DesktopDC, Screen.Width, 0);
12    pcTekst := 'Finn Tolderlund';
13    SetTextColor(DesktopDC, clBlue);
14    Rectangle.Left := 150;
15    Rectangle.Top := 250;
16    Rectangle.Right := 150 + 100;
17    Rectangle.Bottom := 250 + 100;
18    SetBkMode(DesktopDC, Transparent);
19    DrawTextEx(DesktopDC, pcTekst, -1, Rectangle, DT_CENTER or DT_NOCLIP, nil);
20    ReleaseDC(GetDesktopWindow, DesktopDC);
21  end;