This tool is widely use in Blade Runner 2049. All the CG rain are created by the same tool and rendered in Clarisse. Artists are able to finish the setup of rain in minutes and start manipulate the dynamic parameters.
Starts with the source geometry. By default, the simulation splits into 3 different layer according to the distance from the camera, 0-200m, 200-400m, and 400-1000m. The tool is able to track the path of the camera automatically, and create the roof, side wall, visible area SDF, and etc.
We applied the noise on top of the source geometry with special pattern, to simulate the realistic rain pattern. Which means, we can feel the nature distribution of different dense of the rain. The simulation also comes with the realistic wind blowing, which is driven by a 3D noise. Which means the wind is blowing with different strength in space, not constantly.
After the first step of simulation, we can use the "Particle Cache Replicate" which create a super dense of rain in procedural way. The replicate tool reads the same cache with different timeshift. Applied with the individual noise to each reads, we can increase the dense in few seconds without generating huge data of cache.
We will crop out the particle for each layer according to the distance from the camera mentioned before. This is able to solve the shot with camera pushing forward, especially for those spinner flying shots.
At last, we export the cropped cache for each layer to lighters rendering in Clarisse.
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