In an age when video-game demos are on the verge of extinction, Firaxis and 2K Games decided to stand up and show to the public how gamers should be treated. So, strategy fans, get ready for a treat as a demo for Sid Meier’s Civilization: Beyond Earth can be downloaded right now from Steam.
In addition, Firaxis has published a post explaining how the team approached multi-GPUs via Mantle in order to eliminate micro-stuttering and offer an experience similar to Single GPUs.
As Firaxis’ John Kloetzli claimed, while AFR offers – most of the time – an amazing increase of the average framerate, it does come with some shortcomings.
“Current multi-GPU solutions are implemented in the driver, without knowledge of, or help from, the game rendering engine. With the limited information available drivers are almost forced to implement AFR, or Alternate Frame Rendering, which is an approach where individual frames are rendered entirely on a single GPU. By alternating the GPU used each frame, rendering for a given frame can be overlapped with rendering of previous frames, resulting in higher overall frame rates. The cost, however, is an extra frame of latency for each GPU past the first one. This means that AFR multi-GPU solutions have worse response time than a single GPU capable of similar frame rates.”
Therefore, Firaxis decided to use SFR (split frame rendering) in Sid Meier’s Civilization: Beyond Earth via Mantle.
“Rather than trying to maximize frame rates while lowering quality, we asked ourselves a question: How fast can we get a dual-GPU solution without lowering quality at all? In order to answer this question, we implemented a split-screen (SFR) multi-GPU solution for the Mantle version of the game.”
According to Kloetzli, SFR breaks ‘a single frame into multiple parts, one per GPU, and processes the parts in parallel, gathering them into the final image at the end of the frame. Firaxis chose this mode due to the design of the Civilization rendering engine, and because this method does not bring micro-stuttering to the table. However, the drawback here is that SFR is slower than AFR.
Kloetzli concluded that multi-GPUs should start offering an experience similar to the one provided by Single GPUs, despite all the shortcomings that SFR introduces.
“We do not claim to have the perfect multi-GPU solution with Civilization: Beyond Earth, and our current implementation has does have some limitations. Our split-screen rendering probably won’t get the same frame rates as AFR techniques, and we are currently limited to 2 GPUs. Some machines (especially those with slower CPUs) may not see high performance gains, and the highest gains will be seen at higher resolutions. However, we believe the time is ripe for multi-GPU machines to provide a user experience just as good as single-GPU systems, and with the explicit multi-GPU control provided by AMD Mantle we have started working to make this a reality.”
It remains to be see whether SFR is the way to go or not, especially when NVIDIA has done an incredible job at almost eliminating micro-stuttering on SLI systems (that run in AFR mode)!