At the Game Creators Conference 2017 in Osaka, Cygames hosted a panel titled “Research on Real Time Cloud Display and Introduction of Technology in Granblue Fantasy Project Re: Link.” Recently, slides from the presentation have been published, and you can see them at the bottom of the post.
Granblue Fantasy Project Re: Link is a PS4 exclusive JRPG coming in 2018, developed in collaboration with PlatinumGames, and the focus of Cygames’ project to make a break into the home console market with their most famous mobile IP, Granblue Fantasy.
As the title suggests, the presentation focused on the the visual display of the sky and clouds of Granblue Fantasy in a 3D environment. Those familiar with the original mobile game will know that the sky is an extremely relevant part of the IP’s setting, and its clouds are very iconic. Thing is, the mobile game is fully 2D, so moving it to 3D rendering requires new tech and research.
The aim of developers is to display the grand, delicate and pleasant look of the world, with a giant sky that dominates everything. This is done by combining recognizable clouds with a mysterious, fantasy-like appearance.
Anther important element is to add on top of a realistic representation with the expressiveness of color, firmly rooted in the use of shadow. On top of that, the clouds should not be considered by themselves, but they should appear like they belong to the same world as the rest of the environment, with the boundaries between them becoming ambiguous.
The question developers had to face is how to showcase this “sky world” in 3D.
In order to represent the clouds in GranBlue Fantasy, it’s important to have formations that spread across an “infinite plane,” creating the concept of “Plane Clouds.” Below you can see a few screenshots of what they look like.
In order to define the Plane Clouds, a few elements need to be known: The first is what clounds actually are, the second is is how to shape Plane Clouds, the third is the optical laws governing them, and the fourth is Ray Marching.
First of all, clouds aren’t gas. They’re part liquid and part solid. They’re composed of droplets of water floating between 0.5 and 2 Km from the ground. Clound are also created as the exhaust gases of an airplane turn into water droplets or ice crystals. Basically, a cloud is an agglomerate of water droplets and ice crystals.
There are various way to create the shape of clouds, and Cygames studied the procedural cloud generation method that uses volumetric noise textures. The reference study used was “The Real-Time Volumetric Cloudscapes of Horizon Zero Dawn” by Guerrilla Games.
By putting together two techniques named Perlin Noise and Worley Noise, they can create clouds that are large and fluffy. The result is named Perlin-Worley Volumetric noise texture.
After generating the shape of the clouds, it’s necessary to add the effect of optical laws. In order to create the correct lighting, it’s necessary to simulate the way light passes through the clouds themselves. In the screenshots below you can see the difference between the clouds without and with lighting applied.
Optical laws introduced are those that apply to liquids, including the Lambert Law, the Beer law, and their combination, the Beer-Lambert Law, taking in account the optical depth and absorbance of the cloud, related to its density and thickness.
Ray Marching is used to measure the cloud’s density since it’s not consistent. There are thin areas and thicker areas, and measuring density via Ray Marching helps creating the shape and lighting of each cloud.
While Ray Marching is very helpful, it’s very costly in terms of performance, so developers had to take a series of steps in order to make the process manageable.
While the Plane Cloud tech is powerful, it has a weakness: being generated mechanically, it cannot properly display Granblue Fantasy‘s iconic Cumulonimbus with unique shapes, so another technique named “Arbitrarily Shaped Cloudd” had to be implemented on top of the rest.
This allowed to create large clouds volume-wise, to easily alter their shape, and to let the camera actually get into the clouds.
The method used was to create the clouds by combining spheres. It’s simple, fast and easy, and when you put spheres together, the shape is already similar to a cloud.
At first, storing geometry in 3D textures defined by ray marching seemed to be the way to go, but it was ultimately discarded as the cloud generated were different from the Plane Clouds and caused problems when scaling. Defining the space with spheres generated clouds similar to the Plane Clouds, which is why it was adopted by the developers.
Then the team also had to consider the fact that there are many cases in which multiple clouds overlap in the camera’s line of sight. Clouds are sorted in order as there is a point after which their combined density ends up stopping the light, which means that anything beyond that doesn’t need to be displayed.
The same process has to be applied to the sunlight, that has to be displayed after passing through multiple clouds. However, since Ray Marching is a costly process in terms of performance, the team is considering an alternative shading technique that doesn’t make use of it.
As a result of this research, it was possible to create arbitrarily shaped clouds that can be displayed correctly even when combined dynamically. They can move and change shape by changing how they are combined.
We also see how Plane Cloud and Arbitrarily Shaped Cloud can be combined. It’s worth noting that this was created by an engineer, and developers are confident that an artist will do an even better job.
The technology is still in its infancy, and the clouds generated still aren’t a match from the true image of GranBlue Fantasy. Various adjustments need to be made, including optimization, lighting processing and blending with other objects and the environment.
That said, developers are confident that they’ll manage to recreate the beautiful world of GranBlue Fantasy as expressed by the illustrations, and they will continue to work hard to deliver the best game possible.
Below you can see the full presentation used for the panel.
Granblue Fantasy Project Re: Link is scheduled to release in Japan in 2018, exclusively for PS4. If you want to check out some recent screenshots, you can find them here.