Volumetric Billboards

We introduce an image-based representation, called volumetric billboards, allowing for the real-time rendering of semi-transparent and visually complex objects arbitrarily distributed in a 3D scene. Our representation offers full parallax effect from any viewing direction and improved anti-aliasing of distant objects. It correctly handles transparency between multiple and possibly overlapping objects without requiring any primitive sorting. Furthermore, volumetric billboards can be easily integrated into common rasterization-based renderers, which allows for their concurrent use with polygonal models and standard rendering techniques such as shadow-mapping. The representation is based on volumetric images of the objects and on a dedicated real-time volume rendering algorithm that takes advantage of the GPU geometry shader. Our examples demonstrate the applicability of the method in many cases including levels-of-detail representation for multiple intersecting complex objects, volumetric textures, animated objects and construction of high-resolution objects by assembling instances of lowresolution volumetric billboards.