Matthew Benson
Technical Director
Introduction
This was my most recent project, the goal was to upgrade our entire vegetation interaction pipeline. Our old system involved artists having to hand place and animate spheres to move vegetation around. Artists did not have a reliable way of visually seeing what the vegetation was doing until render time. This resulted in a massive tax on the Simulation department, and most of the time it was just easier to remove any grass that was too close to a character.
Wish List
One of the first steps was to gather information about what the department's needs were after talking to a couple of the supervisors and some TD's that had used the old system the following "wish list" was formed for the new Pipeline:
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To have control down to individual blades of grass
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Dontrols for physics of vegetation
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Plasticity
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Direct visual feedback before render time.
Overview
I created a pipeline built on USD, Python and Houdini which allowed artists to easily simulate vegetation interaction. it creates a box based on a characters movement, scans the scene for any at render time procedurals that exist inside of that box. It bakes all of those procedurals into use geometry, stores them in our global repository. Then it creates a kill box that talks to the procedural generator so that we don’t end up with double geometry (procedural and our USD layer). The USD geo can then be brought into Houdini where a simulation artist can adjust physical parameters such as bend stiffness and plasticity gravity ect. and run a physics simulation where they collide with the characters brought in. The sim data is then exported as a USD overlay that is sub layered on top of the original bake.
Rollout
Teamed up with Pixar university to create a three day intro to Houdini course. This course taught the basics of Houdini and on the last day we use the new pipeline and sim a shot. I ran the class for the simulation department. I additionally created comprehensive documentation on how to use the pipeline as well as a website with easy to find tricks and tips.
Usage
Before my pipeline a shot with Vegetation interaction would take about 2 weeks to complete. Afterwards a single artist was able to turn around between 8 to 10 shots per week.. It has been used on 100s of shots and 4 feature productions. The Pipeline has saved hours of time, and the results look much more physically accurate. Continued improvements are on going.
