unit AppMain;

interface
uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, StdCtrls, ExtCtrls;

type
 TForm1 = class(TForm)
   ListBox1: TListBox;
   PaintBox1: TPaintBox;
   Button1: TButton;
   procedure FormCreate(Sender: TObject);
   procedure Button1Click(Sender: TObject);
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

function EnumWindowProc (Wnd: HWND; param: LPARAM): Integer; stdcall;
var
 AClassName: array[0..255] of char;
begin
 with TForm1(param) do
 begin
   GetClassName(Wnd, AClassName, SizeOf(AClassName));
   ListBox1.Items.AddObject(AClassName, TObject(Wnd));
 end;
 Result := 1;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
 Wnd: HWND;
 ADC: HDC;
begin
 if ListBox1.ItemIndex > -1 then
 begin
   Wnd := HWND(ListBox1.Items.Objects[ListBox1.ItemIndex]);
   if IsWindow(Wnd) then
   begin
     ADC := GetWindowDC(Wnd);
     try
       with PaintBox1.ClientRect do
         StretchBlt(PaintBox1.Canvas.Handle, Left, Top, Right - Left,
           Bottom - Top,
           ADC, 0, 0, Right - Left, Bottom - Top, SRCCOPY);
     finally
       ReleaseDC(Wnd, ADC);
     end;
   end;
 end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 EnumWindows(@EnumWindowProc, LPARAM(Self));
end;

end.

function EnumWindowProc (Wnd: HWND; param: LPARAM): Integer; stdcall;
var
 AClassName: array[0..255] of char;
 CS: DWORD;
begin
 with TForm1(param) do
 begin
   GetClassName(Wnd, AClassName, SizeOf(AClassName));
   CS := GetClassLong(Wnd, GCL_STYLE);
   if (CS and (CS_OWNDC)) <> 0 then
     ListBox1.Items.AddObject(AClassName, TObject(Wnd));
 end;
 Result := 1;
end;

unit main;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs;

type
 TForm1 = class(TForm)
 protected
   procedure CreateParams (var Params: TCreateparams); override;
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

{ TForm1 }

procedure TForm1.CreateParams(var Params: TCreateparams);
begin
 inherited;
 Params.WindowClass.style := Params.WindowClass.style or CS_OWNDC;
end;

end.