procedure TDirectDrawCanvas.CreateHandle;
begin
  if FDeviceContext = 0 then begin
    FEnabled := FSurface.GetDC(FDeviceContext) = DD_OK;
    if FEnabled then
      Handle := FDeviceContext
    else begin
      Handle := 0;
      FDeviceContext := 0;
    end;
  end;
end;

使い方は
 Canvas := TCanvas.Create(BackBufferSurface);
しておいて
 with Canvas do
  if Enabled then try
   Pen.Style := psSolid;
   :
  finally
   Release;
  end;