Article author here. Check the emacs-devel thread: some people were able to repro the flickering and some couldn't. It appears to depend heavily on details of your machine.
I have two X1 Carbon 4th Gen machines, one running Goobuntu (basically Ubuntu 14.04 with a new kernel) and one running Ubuntu 16.10. They both flicker, but differently.
Black and white horizontal lines or misrendered text for a split second until a white blink rerenders the whole page. Happens somewhat frequently when I have heavy CPU load on a Linux laptop.
It definitely flickers a bit when running in XQuartz.
(I hope this change doesn't make it run crappily in XQuartz! X-Windows programs that do double buffering draw to an offscreen buffer often perform really poorly, poorly enough that I'd definitely rather have the flicker, not least because I don't mind the flicker too much anyway.
(I assume a lot of them have a client-side pixmap that's written to manually, and then has to be sent over the network link. )
One of the advantages of using the X double buffer extension or XRender or something like that is you don't need to send raster image data over the network. You're still sending ordinary drawing commands, and it's the server that accumulates the results into a pixmap somewhere.
If it is slow for you, you can turn off the new stuff:
Same question I was about to ask. I use emacs on Ubuntu every day and I don't remember it flickering. I wouldn't use it if it were. Well, maybe I'll look for another OS.
Ditto, stock 14.04 Trusty running Unity, and this was also true for Debian releases lenny through wheezy, and at least two very different hardware systems.
I do experience flickering, on both a desktop Fedora 22 system and a X1 carbon 4th gen system running OpenBSD 6.0. It is usually mostly noticeable in the fringe area as well as along the divider when splitting windows. Kuddos for OP, the patch does not seem trivial and it is a most welcome change.
