Brollywood
Making it rain
Making large scenes rain for real can be impractical and very expensive. Lots of water, rain stands, hoses, cranes are needed and even then it's not possible to cover the area required for these scenes.
First needed to generate a surface for it to land onto. For this, we were able to use a proxy CG model of the bridge that had been generated in pre-production for use in shot planning. Once the matchmove had been completed we were then able to start generating CG rain elements, namely falling rain and also rain ‘splatter’ on horizontal surfaces.
The falling rain was produced using Nuke’s 3D particle system functionality. A processor intensive process that also required a number of revisions to get right, we relied on AWS’s elastic computing power as well as Deadline’s AWS spot-rendering integration to give us the processing power we needed for the particle simulation. This dramatically reduced our iteration time per shot from days to hours, allowing us to refine the look of the rain quickly and efficiently to match the rain in the practical shots.
We employed the same process for the rain splatter, using the proxy geo generated in the initial stages of the shot pipeline to generate a randomised particle system of rain splatter sprites, emulating how real rain splatter looked.
Once both the falling rain and rain splatter elements had been produced, we could then start integrating them into the shots. The falling rain elements were generated with depth passes meaning that a sense of depth/atmosphere could be adjusted to suit the shot. We also employed more conventional techniques such as adding smoke elements to the shots to act as very subtle spray clouds which both added to the depth of the shots but also randomised the perceived rain movement as per a real storm. For the rain splatter, additional elements such as noise were added to it, making parts of it feel like it has puddled. For any real puddles that were still on the day this same noise technique was used to distort the reflection, further integrating the CG into the shot and matching it to the real shots.
These steps were then repeated for all 30 shots to produce a seamless VFX rain sequence and particle simulation that immersed the viewer in the story and gave the scene a sense of chaos the creative team had strived for.
