Intentionally blur the screen on OS X? Hey is there a tool that blurs my screen output in real time? It'd be perfect if it only blurred my external display but everything's fine. 

I am on El Capitan now
The Xscope app has a presbyopia filter that does a light blur.


http://xscopeapp.com


I see several large screen sizes, but you might not get your whole screen blurred. It works very well on the latest release of OS X and you can try it out for free I believe. If you're a programmer and not just looking for a ready-made tool, you would do worse to try something other than Brad Larson's tutorial on GPU accelerated video processing at http://www.sunsetlakesoftware.com/2010/10/22/gpu-accelerated-video-processing-mac-and-ios