  Searching for a unified scene representation remains a research challenge in
computer graphics. Traditional mesh-based representations are unsuitable for
dense, fuzzy elements, and introduce additional complexity for filtering and
differentiable rendering. Conversely, voxel-based representations struggle to
model hard surfaces and suffer from intensive memory requirement. We propose a
general-purpose rendering primitive based on 3D Gaussian distribution for
unified scene representation, featuring versatile appearance ranging from
glossy surfaces to fuzzy elements, as well as physically based scattering to
enable accurate global illumination. We formulate the rendering theory for the
primitive based on non-exponential transport and derive efficient rendering
operations to be compatible with Monte Carlo path tracing. The new
representation can be converted from different sources, including meshes and 3D
Gaussian splatting, and further refined via transmittance optimization thanks
to its differentiability. We demonstrate the versatility of our representation
in various rendering applications such as global illumination and appearance
editing, while supporting arbitrary lighting conditions by nature.
Additionally, we compare our representation to existing volumetric
representations, highlighting its efficiency to reproduce details.
