Compromise. It’s something many VR developers today deal with in their ongoing quest to nail the right mix of technical features and computational power for the best balance of performance and visual fidelity. Many of today’s big game engines use a technique called deferred rendering. Deferred rendering does all of the geometry work first and then shades pixels.That worked well on the last generation of consoles, but it’s not a great fit for VR.
With the forward rendering path in Unreal Engine 4, developed by the amazingly talented engineers at Epic, developers have more choice in how they render for VR, helping to achieve a stunning-looking game while delivering the high frame rates necessary for a good experience.
Discussed on stage at AMD’s “Capsaicin” webcast and press event at the 2017 Game Developers Conference, the forward rendering path provides a strong alternative to the popular deferred rendering method, allowing developers to hit the demanding frame rates necessary for smooth VR experiences with improved image quality. Forward rendering has been showcased in games such as Epic Games’ Robo Recall, and is planned in upcoming VR titles from awesome developers like First Contact Entertainment, Limitless Studios, and Survios.
Technically Speaking: Deferred vs Forward Rendering
Let’s dig in and talk about this a bit. Deferred rendering has a performance cost for each frame, in addition to higher GPU memory and bandwidth requirements compared to forward rendering . While deferred rendering does support some nice features like screen-space reflections, those features are generally too costly to use given VR’s ~90FPS requirement.
Current head mounted display (HMD) resolutions being what they are, VR also really benefits from high-quality edge smoothing. Deferred rendering unfortunately doesn’t mix well with multi-sampled anti-aliasing (MSAA) because there are performance and image quality issues. But MSAA is arguably the best AA technique for VR. Post-process AA methods like FXAA don’t work terribly well with stereo views in VR. If you’ve tried a game that uses it, you know it doesn’t look good.
All told, AMD feels that deferred rendering exacts a toll in terms of time, memory, and image quality in VR, and the payoff just isn’t there.
The alternative here is to adopt a form of forward rendering. Interestingly, it’s not a new technique; in fact it’s how GPU rendering started. It’s lighter weight, simpler, and faster. Also, forward rendering works nicely with MSAA, letting us improve edge quality very efficiently. So we think forward rendering is often a better fit for VR applications.
We’ve worked diligently to test and optimize the forward rendering path in Unreal Engine 4.15 for the best performance on AMD hardware. A number of VR development partners are using Unreal Engine, and we showed the performance benefits during our Capsaicin event at GDC.
“AMD has been on a continuous mission to make VR accessible to as many people as possible, and Epic’s forward rendering path in Unreal Engine 4 is a big step in that journey,” said Raja Koduri, Senior Vice President and Chief Architect, Radeon Technologies Group, AMD. “Anyone who has experienced Epic’s Robo Recall will immediately attest to the benefit of forward rendering in VR. We are working with VR developers to explore the benefits of forward rendering, which can result in beautiful, high-performing games on Radeon graphics.”
AMD is working with leading game developers to explore the benefits of forward rendering in VR games, including:
- First Contact Entertainment: First Contact Entertainment’s breakout game, “ROM: Extraction” is one of the most visually appealing and exciting VR releases, debuting this past December to rave reviews. Available today, First Contact Entertainment is releasing “Overrun,” a new content expansion to ROM: Extraction that makes use of forward rendering for unprecedented performance.
- Limitless Studios: Directed by Matthew Ward and built in virtual reality using the Limitless VR Creative Environment, “Reaping Rewards” is an interactive VR experience exploring the emotional choices of a young Grim Reaper as you learn about life and death from your mentor. This interactive character-driven story harnesses forward rendering to bring the experience to life.
- Survios: Since its Early Access release last year, Survios’ critically-acclaimed and award-winning game “Raw Data” has become a must-have title for all VR gamers. At AMD Capsaicin, Survios unveiled their highly-anticipated new title: “Sprint Vector,” which makes use of Unreal Engine 4.15 and forward rendering. An intense adrenaline platformer, Sprint Vector uses a unique intelligent fluid locomotion system to propel players through high-speed head-to-head races through challenging interdimensional obstacle courses.
Scott Wasson is Sr. Technical Marketing Manager for the Radeon Technologies Group at AMD. His postings are his own opinions and may not represent AMD’s positions, strategies, or opinions. Links to third party sites and references to third party trademarks are provided for convenience and illustrative purposes only. Unless explicitly stated, AMD is not responsible for the contents of such links, and no third party endorsement of AMD or any of its products is implied.