In Canvas eines externen Fensters zeichnen

[Popov]

Code funktioniert, dein Problem muss also irgendwo anders liegen.

Delphi-Quellcode:

uses
  ShellApi;

procedure TForm1.Button1Click(Sender: TObject);
var
  destWnd, destHdc: hdc;
  destCanvas: TCanvas;
begin
  ShellExecute(0, 'open', 'notepad.exe', nil, nil, SW_NORMAL);
  Edit1.Text := 'Unbenannt - Editor';
  Sleep(500);

  destWnd:= FindWindow(nil, pchar(Edit1.Text));
  if destWnd = 0 then
  begin
    ShowMessage('Did not find window handle of ' + Edit1.Text);
    exit;
  end;
  destHdc:= GetDc(destWnd);
  if destHdc = 0 then
  begin
    ShowMessage('Did not get DC of window');
    exit;
  end;

  destCanvas:= TCanvas.Create;
  destCanvas.Handle:= destHdc;

  destCanvas.Brush.Color := clRed;
  destCanvas.Rectangle(10, 10, 100, 100);
  destCanvas.Refresh;

  destCanvas.Free;
  ReleaseDc(destWnd, destHdc);
end;