Clouds in the Cloud: Efficient Cloud-Based Rendering of Real-Time Volumetric Clouds

Volumetric clouds play a crucial role in creating realistic, dynamic, and immersive virtual outdoor environments. However, rendering volumetric clouds in real-time presents a significant computational challenge on end-user devices. In this paper, we investigate the viability of moving computations to remote servers in the cloud and sharing them among many viewers in the same virtual world, without compromising the perceived quality of the final renderings. We propose an efficient rendering method for volumetric clouds and cloud shadows utilizing caches placed in the cloud layers and directly on the surface of objects. Volumetric cloud properties, like density and lightning, are cached on spheres positioned to represent cloud layers at varying heights. Volumetric cloud shadows are cached directly on the surfaces of receiving objects. This allows efficient rendering in scenarios where multiple viewers observe the same cloud formations by sharing redundant calculations and storing them over multiple frames. Due to the placement and structure of our caches, viewers on the ground still perceive plausible parallax under movement on the ground. In a user study, we found that viewers hardly perceive quality reductions even when computations are shared for viewers that are hundreds of meters apart. Due to the smoothness of the appearance of clouds, caching structures can use significantly reduced resolution and as such allow for efficient rendering even in single-viewer scenarios. Our quantitative experiments demonstrate computational cost savings proportional to the number of viewers placed in the scene when relying on our caches compared to traditional rendering.