Just thought I would share my experience in using Zwift with a Mackbook Pro (2017 - 15") with an external GPU (eGPU) box with an AMD Vega 64 GPU. I’m using the Sonnet Breakaway 650w box with the Vega 64 (technically the ASUS ROG Strix Vega 64 flavor) installed in it and connected to the MBP via Thunderbolt 3. The Vega 64 is then connected to a 49" 4K tv via HDMI.
The good is that it works pretty darn well, without a ton of effort. There’s a couple of hiccups that I’ll explain below. The external GPU box has allowed me to keep my setup very simple, and not have to maintain/update/troubleshoot/support an entirely separate PC just to run Zwift. I like simple.
With the release of High Sierra 10.13.4 recently, Apple has officially enabled eGPU support for Macs. The first thing I figured out is that because Zwift locks into the GPU (and subsequent quality and resolution settings) upon initial startup, I have to start Zwift with the MBP closed in clamshell mode. This forces Zwift to start on only the TV, which is being powered by the Vega 64. If I start Zwift with the MacBook Pro open, it starts running on the Mac’s internal screen, which is powered by it’s own discrete GPU, and will not setup properly for the Vega 64 if I drag it to the second monitor (the tv in this case).
Unfortunately, Zwift does not recognize the Vega 64 as a high-end card and locks me in on the ‘High’ quality setting and will not go above 1440p in game.
I have manually edited my ‘High’ config file, and the ‘prefs.xml’ to enable Ultra settings at 3840x2160 resolution. This seems to work well, as I’m getting 35-75fps with everything maxed at 4K (more on this in a minute). Hopefully Zwift will update to properly recognize the Vega 64 to enable Ultra and 4K resolution by default; I have opened a support ticket for this.
The Ultra settings in 4K is pretty amazing. I have read in other posts that Zwift deprecated most of the settings from the quality files (Ultra.txt, High.txt, etc.), so I’m not sure if I’ve even reached the visual pinnacle. Some things from this file do still stick (e.g., FPS readout on screen and shadow resolution) that you can see in the log file after. I really wish Zwift made this kind of advanced configuration easier and documented (or at least possible).
The frames-per-second is adequate as far as I’m concerned, with me hitting 35-75 fps on Ultra at 3840x2160. I hit higher frame rates in the rural areas, and lower frame rates in the urban areas where there are more riders (like London). I just did a 90 minute London ride today where frame rates were around 35-45 for most of the urban sections, but when I was done, I noticed that the none of the 3 fans on the GPU board, nor the fan for the eGPU enclosure itself were kicked on. The thing was not even warm. So this tells me that there is still a TON of potential to be had from the Vega 64. A lot of this probably has to do with optimizing the built-in Apple drivers for AMD GPUs, but I bet Zwift has their own work to do that would improve visuals while keeping FPS up… because running 35 FPS on a card that’s still cold is kinda weird.
The only other bug I noticed was a 3-way median on the London course was missing it’s texture. It just appeared as white. Otherwise it was good to go.