Support of indirect GLX (iGLX) in XQuartz.
An update from X11.org
On Thu, 2016-05-26 at 16:34 +0000, Cook, Rich wrote:
Hello, I recently heard on the Apple x11-users mailing list that remote OpenGL rendering (IGLX) is being phased out of XOrg and not being replaced. Is this really the case or am I misunderstanding?
You have heard incorrectly. It is disabled by default for security reasons, as it's been a repeated source of exploitable bugs, but the feature itself isn't going away.
One caveat is there's no easy way to enable it other than the command line, and not all display managers give you a mechanism to pass arbitrary options in (which is reasonable enough). I've added an xorg.conf option to enable IGLX in master, and I'll be backporting that to the various stable branches as well.