Real-time accumulation of occlusion-based snow
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This paper describes a technique to allow the real-time simulation of snowfall accumulation in a dynamic 3D environment. The implementation maps surface-bound accumulation buffers to each object in the scene, forming height-maps of accumulated snow cover. The environment is rendered from above similar to the way shadow mapping is typically produced. However, unique buffer IDs and texture co-ordinates are output within each pixel of the render. A new technique for performing the mapping between buffers is proposed where a series of quads are rendered, one per pixel of the occlusion projection, to map directly visible surfaces to their corresponding accumulation height-map. Blurring is performed on the maps and per-pixel detail is given by procedurally generated normal maps of each surface updated frame by frame. Additional detail and shaping is performed using view-dependent tessellation and the snow surface is created by re-colouring and offsetting the existing scene geometry. This is the first implementation of snow simulation which allows persistent accumulation on a dynamic, moving scene in real-time.