Emerging Technology – The Rise of Physical Based Rendering and Material Authoring Tools
Physically Based Rendering (or “Shader”) uses lighting techniques which mimic how light interacts with materials and surfaces in natural environments to achieve organic and accurate textures. PBR was pioneered within the animation industry for use in pre-rendered scenes and films, most notably in the famous Walt Disney Pictures and Pixar Animation Studios. Due to advances in technology and computational power, this now allows us to use PBR in real-time rendering, with a multitude of game engines including Unreal Engine, Unity and CRYENGINE supporting it.
PBR is quickly becoming the norm and workflow of choice in the gaming industry, with a great majority of AAA titles and studios following the trend, including Naughty Dog’s Uncharted 4, Guerilla Games’ Horizon: Zero Dawn and DICE’s Star Wars Battlefront. DICE’s producer, Craig Mcleod, during the game’s production went on to say in an interview with GamesBeat:
“It allows our surfaces to be physically rendered. What that means is they react in an incredibly realistic way based on light, so it’ll bounce light depending on how that changes. So it’s not just one setting, but it actually feels like it’s truly in the environment.”
–Craig Mcleod, Game Producer at DICE
However, PBR is not just at the forefront of visuals and lighting in game development and animation studios. It is being used by some of the leading visual effects houses in the world on some of the latest blockbuster films, including Marvel’s Logan (Logan, 2017) and Assassin’s Creed (Assassin’s Creed, 2016). These effects are being created by studios like Double Negative, Image Engine and Rising Sun Pictures, alongside many more. Furthermore, PBR has also been adopted within architecture and design sectors, with companies including Ikea and AutoDesk using these techniques when creating their products.
Physical Based Rendering is more of a concept and a set of guidelines to follow to achieve realistic light behaviour. This means the artist must adhere to the rules of energy conservation, meaning no surface can reflect more light than it takes in.
Diagram displaying how light reacts upon hitting a surface.
The albedo map will hold all the basic flat colour and intensity information for your material, and should no longer hold any highlight or shadow information. Therefore it is either separate from any ambient occlusion or removed altogether. This will result in the material appearing correct in any lighting situation.
Surfaces can be split into two groups, dielectrics (insulators) and metals (conductors). The metalness map simply defines whether a surface is metal or not, therefore this is typically set to 0 (black) for non-metals or 1 (white) for metals – with any values inbetween rarely being used. When the surface is a metal this pulls the colour information from the albedo map (which is usually very minimal), which will cause any reflections to be tinted accordingly. Usually, as the metalness increases, the base colour will darken.
Metalness ranging from 0 to 1
When texturing a model using physical based materials the main difference to older techniques is the way that the specular map is utilised. Originally, the specular map adjusted the levels to vary the intensity of the highlights. However, using newer techniques, a roughness map will be used instead. The roughness map will offer much more than the traditional specular map as it will affect the vividness of a highlight, but also the size and how detailed (or blurred) the reflections are of the surrounding environment. This means a roughness value of 0 will appear as a sharp and more narrow reflection and be completely smooth with no surface imperfections. A value of 1 will appear matte, as the surface is so rough that it causes the light rays to scatter/diffuse, resulting in a wide and blurred reflection.
Roughness ranging from 0 to 1
The above albedo – metalness – roughness workflow can be used to varying degrees to achieve any material imaginable, which is the main difference when compared to traditional texturing. The incorporation of normal and ambient occlusion maps remains the same, although the latter is now no longer a necessity.
Before the introduction of the PBR workflow, artists would have to carefully plan and create a 3D asset’s texture to match and compliment that of pre-agreed lighting and environmental parameters. As a result, if a change were to be made to any of the lighting conditions within a scene, often multiple assets would need to be tweaked manually to re-balance the environment, which is ultimately very time consuming.
“I use Substance Designer to do everything at work as it supports our tools and workflows. I think this suits a production environment a lot better because you can always iterate on anything that is made across the art team. If you need to change a material, you can go back at any point.”
–Ben Keeling, Environment Artist at Creative Assembly
Any assets created using the PBR workflow will adapt to the lighting and colouration of the surrounding environment, and will be reflected to varying degrees on the surface of the model or material. Therefore, textures will continue to work equally under all illumination variations and react accordingly. This mitigates an artist’s guess-work and removes trial and error from within the workflow. Again, this saves a lot of time.
“…Substance provided us the quality and fidelity to be able to hit our aggressive deadlines with time to spare.”
–Stephen Hauer, Art Director at Camouflaj
Assets created using the PBR workflow react to light following a strict set of rules and calculations, meaning the results are predictable and are no longer down to the artist’s concept and creativity. This may be considered an advantage during production as the creator creates models and textures quickly, efficiently, and predictably. This predictability of an object’s appearance when placed in the final scene lowers the risk of design mistakes. However, it may also be considered a disadvantage due to its consistent results. The PBR workflow process is sometimes easy to recognise, suggesting that assets created using it may appear immediately discernible within a project.
These predictable results may be the reason that PBR is often mistakenly limited by artists to creating realistic surfaces and materials. However, in my opinion, the PBR workflow is equally practical when creating stylised art. Whether you’re creating an asset to be placed in a scene replicating real-life or that of hand-painted fantasy, you will always want it to respond correctly to its surrounding environment to allow for a consistent visual art style. This is where PBR, in my opinion, really shines.
A perfect example of this recently, although not from within game design, is the visuals created on Disney Pixar’s Monsters University (Disney Pixar, 2013), which used PBR techniques to produce a full feature length animated movie. This practice is now becoming more common within film as technology progresses.
A scene from Monsters University (Disney Pixar, 2013)
With the continuing evolution of PBR there has been the development of numerous 3D Painting and Material Authoring Software to utilise it, with Allegorithmic’s Substance Painter and Substance Designer Software especially growing in popularity across the creative industry. This software faces stiff competition from similar applications such as Quixel Suite and Pilgway’s 3D Coat. However Allegorithmics’ product boasts an 85%-plus adoption rate in AAA games studios, making it the industry’s current “go to” texturing tool.
“Allegorithmic has been re-imagining the process of texture creation since 2003. Today, over 85% of AAA game studios use Substance in their production pipelines, making Substance the industry standard for PBR material authoring.”
-Allegorithmic, Official Website
The availability of texture authoring software has seen an influx of materials being created and made available on exchange platforms such as Substance Share and content libraries like Substance Source, both developed by Allegorithmic. The longer this platform is available, the larger the selection becomes, producing an instant library of content for beginners, a base to learn from for those furthering their skills, and a place where even the most highly-talented artists will be able to learn from each others techniques and processes. I feel these community platforms are one of the main ways that physical based rendering and texturing will continue to develop in the future, allowing artists to learn from one another and continue to improve.
PBR works incredibly well when partnered with other modern techniques and software. Many artists now utilise the power of photogrammetry and digital scans when creating realistic assets or materials. Using a multitude of photographs from various angles which cover all of the desired subject then using specialist software such as Photoscan (Agisoft), the use r is then able to rebuild an exact replica in 3D digital space, along with all its colour information. These colours can then be transferred onto an albedo map, once all lighting information has been removed (as discussed above). Photogrammetry results in a dense mesh incorporating all minor details and imperfections. Once retopologised into a more efficient mesh, the original scan can then be baked upon it to produce the normal map. Any additional maps such as roughness and metalness can then be created in order for the asset to react correctly to the scenes lighting, in combination with the newly created normal map.
PBR used in combination with photogrammetry is a powerful combination used in some of the best graphical games of recent times such as The Vanishing of Ethan Carter (The Astronauts, 2014) and Star Wars Battlefront (mentioned above) and the upcoming sequal Star Wars Battlefront 2 (DICE, unreleased) , most commonly used on character and environmental assets. It comes with the advantage of producing colours and details replicate that real-world subject using information from photographs, therefore the time taken for texturing is often reduced. Also, the time allocated on the high-poly modelling is further reduced as the mesh is produced using the images input, allowing the normal (if using a high to low polygon workflow) , cavity and AO maps to be produced quickly.
A screen from The Vanishing of Ethan Carter (The Astronauts, 2014)
Adobe Photoshop can also be used in the making of physical based textures. However it does not support multi-channel painting, meaning each individual map (whether it be base colour/diffuse, roughness, or specular) would have to be created separately. Naturally, the necessity of adjusting each of these values independently makes it much less efficient and much more laborious to change details quickly and accurately.
The Photoshop software becomes a much more potent tool when used in conjunction with any of the new material authoring software, such as aiding in alpha mask creations, transferable decals or any post-processing alterations, with the majority of tools now having plug-ins to allow for direct import and export. Photoshop, for many years, has been the software of choice for many digital artists and this familiarity, paired with any advances in material authoring tools, further augments the artist’s workflow and the possibilities therein.
The use of Physical Based Rendering has steadily increased over the past few years and its growing popularity is an important factor as to why more and more material authoring tools are being developed. As the game and film industries continue to evolve and use this technology, the visual quality of their output similarly continues to rise. This increase can be seen in the most recent films utilising CGI and has assured PBR will stay at the forefront of visual rendering for many years. It comes at a time where graphical improvements are perceived to be slowing down as leaps in technology become smaller and smaller per generation (“diminishing returns”), however there has been a notable upgrade in titles since its introduction. PBR will continue to improve as the familiarity with the technology and supporting software grows.
Physical-based material authoring tools accommodates quick and efficient creation of textures, allowing more assets to be completed within a shorter amount of time. This increase in quality output is extremely beneficial to any team or company. Just as necessity is the Mother of invention, the increased usage of PBR in design industries will necessitate larger steps forward in technology to accommodate greater visions. These increases in technology will further fuel a design demand for more realistic and enthralling visual output, and this cycle will ensure a continuing evolution of pioneering visual effect. I feel that this technology will be a mainstay in the industry in the years to come, and its popularity is borne out by its adoption rate.