Digital Wheat

This project for Dr. Oetker's Yofibra product was technically challenging. The team at Locomotion had to grow digital wheat along a predefined path that had to be integrated into real footage. Our first approach was to use Maya's Paint Effects. The very first tests with Paint Effects were set up quickly but we soon noticed lack of geometric and particularly animation controls that go beyond wind.

We had to grow wheat along the path with control over growth speed randomization, In addition we needed to add three different bend deformations per wheat blade, one to simulate wind, a second to swing each blade back and forth in growth direction and a third to bend the outer blades slighty toward the sides of the path which made the wheat look voluminous and healthy.

Modelling

We modelled several different wheat blades, each with LOD versions to be able to reduce the total polygon count. They were textured with original wheat reference photos taken on location.

Shading, Lighting & Rendering

During R&D phase we started to work out different looks for the wheat. Final goal was to make it look as real as possible. Mental Ray's FG was no option due to high demands on rendering power. Kay finally decided to use GI maps to light the wheat, applying HDRI environments shot on location for indirect lighting. We used the HDRI images as lighting reference for each individual shot. All scenes were lit using original Maya lighting tools and shaders. Using a custom Mental Ray shader programmed by Dirk we could manipulate colors during wheat growth. We rendered several layers and passes to be able to tweak the final look in compositing. Final grading and footage integration was done in Flame at Locomotion.

Software Development

Dirk programmed an API based tool for Maya that allowed us to generate mesh instances on a nurbs surface, based on multiple input meshes and LOD variations. The tool provided a host of growth, bend, transformation and randomization features to be able to control placement, density and motion precisely. Since the polygon count was too heavy for Maya to handle we used an OpenGL approximation to visualize the scene.

The final geometry with transformations and bend deformations was only generated at render time within Mental Ray using a custom geometry shader. Due to the high polygon count we created wheat blades only on demand, as a ray hit an object's bounding box. Using the growth information from the instancing tool we were also able to modify shading depending on the the "age" of each individual blade. This allowed us to start growth with a fresh green and blend smoothly toward the final yellowish color. In addition we could apply a HSV randomization per wheat blade to add natural irregularity in color. Partly the camera was moving quite fast along the wheat geometry, thus we needed to be able to render with motion blur. Motion vector computation was also done in the geometry shader, considering the transformation and deformation of each blade instance over time.