Guerrilla Games shared the production process behind the creation of volumetric cloudscapes in Horizo: Zero Dawn. This is a short part of the presentation held at SIGGRAPH 2015.
Guerilla Games is well-known for the Killzone series. FPS games usually restrict the player to a predefined track, which means that developers just placed clouds using billboards and highly detailed sky domes. This technique is widely used in most 3d games right now. This allows to develop “art directed sky” with lots of details. All you need is Photoshop and some artistic talent. However the studio’s new game Horizon: Zero Dawn demanded a different approach.
Horizon is an open world game. You can explore the land and climb mountains. Developers have simulated the spinning of the earth by modeling a time of day cycle. The weather also changes, so naturally the sky has to change dramatically. The sky also takes a large part of the screen, so Guerilla just had to make it aesthetically pleasing. Here’s what they did.
Artists explored different ways to create and light individual cloud assets. Here’s some quotes from the presentation:
The company decided to go with voxel clouds, although it was not such a popular idea among programmers. They went into Houdini and generated some tiling 3d textures out of the simulated cloud shapes. Using Houdini’s GL extensions, the team built a prototype GL shader to develop a cloud system and lighting model.
Finally, the team got close to mimicking the reference but it all fell apart when they put the clouds in motion. And it was also painfully slow for a game, so the team went another way. They aimed to develop some good noises at lower resolutions that have the characteristics they like and then went out to find a way to blend between them based on a set of rules. It’s pretty complicated stuff, but the results they got are absolutely amazing. There’s more about the production process in the presentation. The developers studied the clouds, analyzed their nature and build an incredible tool to create dynamic and visually stunning clouds.