Game Screen Glitching

Hey guys.

So, I was just playing a game and my screen went all glitchy. There were 'fluttering' bars all over my screen. Anyone else have this issue? It occured on my Alpha client and my normal one. My computer is just fine and it works like a boss, but once it gets into the PvP client with the loading screen, it toast. Also, it occurs the WHOLE game too. Its espically bad when you pull up the Shop or Stats.

Operating System: macOS Sierra (v 10.12)