Game Realism Via NVIDIA Enhanced Effects

By Julian Duque

Earlier this year, NVIDIA introduced the Maxwell architecture and a lot of upcoming features that Benchmark Reviews briefly talked about on the review of the GTX 980 by Olin Coles. These features were demonstrated in detail, but were still pending to be released on actual games, that is until Assassin’s Creed Unity was released earlier this year. Thanks to NVIDIA GameWorks, game developers have the ability to use NVIDIA’s sample libraries and SDKs as well as implementing some of the features mentioned that allow for a more realistic game-play experience.

Aside from much of the criticism NVIDIA and AMD have received for working closely with game developers, this relationship is were the future of the industry lies to create and implement more realistic environments into games. The importance of this relationship is due mainly to the optimization games receive when developers and manufacturers work together. It is through this relationship that we have seen things like FaceWorks, Turbulence, and Mantle come to modern releases and bring a better gaming experience to PC users.

Just like Assassin’s Creed IV: Black Flag, Unity utilizes the AnvilNext Engine, which since it’s debut in Assassin’s Creed lll, has received major updates to include pre-baked Global Illumination, volumetric fog, dynamic weather, and dynamic foliage to name a few examples. Of course, with Unity there is also some major upgrades to the engine from which the most outstanding is Physically Based Rendering (PBR) which enables materials, objects and surfaces to look and react more realistically to lighting, shading and shadowing. Add to that a patch that has enabled the AnvilNext engine to decrease CPU bottlenecking which Unity definitely needs since many gameplay areas are filled with NPCs.

Additionally, there has been a vast improvement of shadowing and reflection effects, depth and field, and textures through Advanced Soft Shadows, Plug and Play Tessellation, HBAO+, and TXAA. For a quick explanation and demonstration of each, continue reading as we explore each of these features found in Assassins Creed Unity.

Back in the day, one of the major problems developers had when trying to bring realism into a game were shadows. Algorithms were usually far from optimal, and generating accurate soft shadows from area light sources proved to be very difficult subject. Soft shadows are important, as they the provide the needed cues about the environment and objects which become sharper near the casting object and softer further away.

NVIDIA tackled this issue by introducing Percentage-Closer Soft Shadows which is based on a shadow mapping and percentage-closing filtering (PCF) algorithm. Instead of the traditional depth comparison of ordinary shadow mapping, Percentage Closing Soft Shadows returns a value that indicates the amount of shadowing at each point when shading occurs each frame. PCSS also uses the relation that as the PCF kernel increases the shadows become softer to accurately represent the casting of an object. This method proves to be really efficient as it requires no pre-processing, post-processing, or additional geometry.

 

Advanced Soft Shadows provides a lot of eye candy, specially in realistically textured scenes which require user interaction. This technique also provides a simple way for developers to add high quality and, most importantly, efficient shadows to games. Additionally, it gives the ability to render cascaded shadow maps, and multiple spot lights. Fortunately, it is not taxing as compared to previous shadowing methods which never succeeded for this same reason.

Probably the most notorious difference between the console version of Assassins Creed Unity, and the PC version is the ability to switch from the old Screen Space Ambient Occlusion technique to the newer and better HBAO+. If all this sounds like another language to you, Ambient Occlusion is a technique used by developers to create realistic shadowing around objects to emphasize the depth of field of each scene.

Like many other graphic settings, Ambient Occlusion has many variants. SSAO has always been the standard but it is already old enough to call the grandfather of graphical settings. Back in 2008, NVIDIA introduced Horizon Based Ambient Occlusion which uses a more complicated algorithm than SSAO, but brought a higher definition, quality, and visibility to AO shadowing. Unfortunately, HBAO proved to be very demanding and most games (such as Battlefield 3) rendered HBAO at half the resolution to compensate for the loss in performance. With the help of DirectX 11, NVIDIA reconstructed HBAO+ to be more efficient, and even added more defined and accurate shadows.

Of course, HBAO+ still takes a higher toll in performance than SSAO, but the impact it has on realism and that next-gen feel that gamers so highly crave make it a very reasonable sacrifice of performance. HBAO+ played an important role in Assassins Creed Unity as each of the vast amount of objects can influence the occlusion of light. Below is a screenshot comparison between HBAO+ and SSAO.

When NVIDIA released TXAA, they were trying to reduce temporal aliasing which produces crawling and flickering in motion during gameplay. TXAA is a mix of the already known Multi-Sample AA (MSAA) along with a custom CG film style Anti-Aliasing and a temporal filter. To correct the sharpness of each pixel structure, TXAA gathers samples from inside and outside the pixel as well as samples from other frames to filter each pixel. This greatly improves the spatial filtering over the standard MSAA filtering and can be clearly seen on objects such as fences and foliage.

Another improvement over FXAA, is TXAA’s capability to intelligently manage per-pixel effects (such as atmospheric rendering) without introducing weird lighting artifacts on structure edges. What is interesting, is that in motion scenes, TXAA can be compared to other high end professional AA algorithms that are usually not available for end users today, but rather on the enterprise hardware from which TXAA was developed from.

 

As you may notice the differences per frame between TXAA, FXAA, and 4x MSAA are almost minimal, however TXAA brings the added benefit of reducing temporal aliasing when in motion throughout the game. The performance impact of TXAA is also different as it varies depending on the type of shading between each game. During our Assassins Creed Unity test we noticed that the performance was relatively similar to that of FXAA.

 

NVIDIA Plug-and-Play Tessellation is an advancement of what used to be GeometryWorks. The Tessellation libraries and tools that NVIDIA has put together allows for developers to greatly enhance the amount of details the players see. With these libraries it is relatively easy to add tessellation to the AnvilNext game engine, allowing to quickly generate tessellation displacement maps suitable for tessellation from pre-existing objects in the library. The library also intercepts DirectX draw calls, analyzes the vertex shader currently being used, and adds its own tessellation shaders, so developers can simply add to the displacement map generated by the Displacement Map Tool.

Tessellation allows what would normally be a single, flat texture that does not alter the lighting, or shadowing of the game to become a single “three dimensional” structure inside the game to which HBAO+ can shadow correctly and affect how PCSS casts over the area. The addition of geometrical detail plays a key role in this, and is what NVIDIA has been working on for quite a while.

 

In Assassins Creed Unity, Tessellation has not yet been released as of the moment of writing this article, however NVIDIA has confirmed that it will bring GeometryWorks DirectX11 with a later update.