PowerPoint.SlideShowSettings oSettings;
  oSettings=Globals.ThisAddIn.Application.ActivePresentation.SlideShowSettings;                         
  oSettings.Run();
  PowerPoint.SlideShowView ssv = Globals.ThisAddIn.Application.SlideShowWindows[1].View;
  if (ssv.PointerType == PowerPoint.PpSlideShowPointerType.ppSlideShowPointerPen)
  {
     ssv.PointerType = PowerPoint.PpSlideShowPointerType.ppSlideShowPointerArrow;
  }
  else
  {
     ssv.PointerType = PowerPoint.PpSlideShowPointerType.ppSlideShowPointerPen;
     ssv.PointerColor.RGB = 123;
  }
  ssv.DrawLine((float)0.0, (float)0.0, (float)150.0, (float)150.0);  画出来的直线屏幕一闪,又没有了