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FX simulations: Clouds, water & destructions
Rise created clouds, water and various types of destruction as FX simulations for the film. Some of these were needed for the film’s own shots, the others were supplied to Walking the Dog. There were many shots in which the birds fly through clouds in the evening sun and also at night. The FX department created these clouds using Houdini’s Cloud Tool and an internally developed cloud loader HDA (Houdini Digital Asset).
With this large number of shots, Houdini’s Mantra Micropoly Renderer proved to be the fastest renderer. To save even more rendering time, the clouds were divided into two types: scattered background clouds and modelled hero clouds in the foreground. The size and position of the background clouds could simply be “painted”. For the foreground clouds, the artists created the basic shape from various interlocking geometries. These shapes were then converted into volumes using Houdini’s Cloud Tool and deformed by a noise during rendering. This had two advantages: The noise could have any resolution, and the artist could see it in the viewport.
A wide variety of water simulations appear in the film: Among other things, a stork falls into the water, a drink is sucked through a straw and birds swim in a swimming pool. To top it all off, there were dramatic waves on steep cliffs. As different as these applications are, they were simulated with relatively little effort using Houdini’s Flip Fluids.
The more difficult part was blending the simulated areas into the geometry, for example into the swimming pool. The aim was not to blend these simulations with the background during compositing, but to be able to use the final rendering as directly as possible and thus make compositing easier. This was particularly important for the simulations that were not rendered in Rise.
Towards the end of the film, a cave collapses over several shots. For these simulations, the artists used Houdini Bullet Rigid Bodies, particles, pyro and grains in a wide variety of shapes. As there was very little time available to process the many shots, it was important to create optimised setups that could be simulated quickly. In some shots you can see how the storks collapse a cave with their beaks. For reasons of efficiency, the yielding of the earth and the formation of cracks were solved using glue constraint clusters and an additional SOP solver (surface operator solver). These solvers increased the cracks more and more with each hit. Of all the simulations, the dust simulation for the collapse of the cave took the longest at around 12 hours, as the dust had to be able to travel from inside the cave up to the distant camera over more than 300 frames in order to create a hidden cut between two shots.
Read more about lighting and shading on page 3
