FormShadow:= NewShadowForm(Form1.Form);
Form1.Form.AttachProc(WndProcFormShadow);

unit FmShadow;
interface

uses Windows, Messages, KOL {$IFNDEF VER120}, Variants{$ENDIF};

function WndProcFormShadow(Self_: PControl; var Msg: TMsg; var Rslt: Integer): Boolean;
function NewShadowForm(pForm: PControl): PControl;

var
FormShadow: PControl;

implementation

var
ShadowSize: Integer = 20;
ShadowColor: TColor = clBlack;
ShadowAlphaBlend: Byte = 120;

function WndProcFormShadow(Self_: PControl; var Msg: TMsg; var Rslt: Integer): Boolean;
var Bounds: TRect;
begin
 if (Msg.Message = WM_WINDOWPOSCHANGED) or
 (Msg.Message = WM_KILLFOCUS) then begin
  GetWindowRect(Self_.Handle, Bounds);
  SetWindowPos(FormShadow.Handle, Self_.Handle, Bounds.Left + ShadowSize,
   Bounds.Top + ShadowSize, Bounds.Right - Bounds.Left,
    Bounds.Bottom - Bounds.Top, SWP_NOACTIVATE + SWP_SHOWWINDOW);
 end;
Result:= False;
end;

function NewShadowForm(pForm: PControl): PControl;
var r: TRect; aWidth, aHeight: Integer;
Src, Dst: HRGN;
begin
 Result:= NewForm(Applet, '');
 pForm.CanResize:= False;
 pForm.StayOnTop:= True;
 pForm.Style := pForm.Style and not WS_MAXIMIZEBOX;
 with Result^ do begin
  HasBorder:= False;
  HasCaption:= False;
  Color:= ShadowColor;
  GetWindowRect(pForm.Handle, r);
  aWidth:= r.Right - r.Left;
  aHeight:= r.Bottom - r.Top;
  Src:= CreateRectRgn(0, 0, aWidth, aHeight);
  Dst:= CreateRectRgn(0, 0, aWidth - ShadowSize, aHeight - ShadowSize);
  CombineRgn(Src, Src, Dst, RGN_DIFF);
  SetWindowRgn(Handle, Src, True);
  AlphaBlend:= ShadowAlphaBlend;
  SetWindowPos(Handle, HWND_TOP, r.Left + ShadowSize, r.Top + ShadowSize,
   aWidth, aHeight, SWP_NOACTIVATE + SWP_SHOWWINDOW);
  DeleteObject(Src);
  DeleteObject(Dst);
 end;
end;
end.

msgok(Form.Caption);
msgok(Form1.Form.Caption);

msgok(Form.Caption);
msgok(Form1.Form.Caption);