When playing a game in which you walk through lush vegetation, Sander Vander Meiren disliked it that all too often the ferns, banana leaves and other foliage do not move - or at least don't respond realistically enough to the player's actions. He wanted to do better.
The first problem he needed to tackle was to find out how instanced static meshes work and how he could get to their properties and replace them with physical foliage blueprints. This was achieved using raycasting.
The physics simulations were not enough, so he added a vertex shader based on distance fields, so the shapes bend more without needing to add more bones to the rig.
Once the walk-through interaction was complete, he moved on to the fun stuff. With physical actors he was able to easily apply forces (i.a.radial explosion impulse) and play an animation to trample the folliage.
The fire propagation posed a bigger challenge. To achieve this a voxel grid was added on top of each instance or actor that needed to catch fire. These cells contain properties like: I’M ON FIRE and an array of the neighbouring voxels so it could pass the fire to the next one if needed.