1. A method performed by one or more processes executing on a computer system, the method comprising: distributing a plurality of sample points across the surface of a three-dimensional (3D) object model to be rendered into a portion of a two-dimensional (2D) image; constructing a hierarchical data structure based on a first subset of the plurality of sample points, the hierarchical data structure comprising a plurality of nodes wherein: one node is a root node; each leaf node is associated with a pre-pass shading sample; and each non-leaf node is associated with a cluster of pre-pass shading samples; and determining a total radiant exitance for a final pass shading sample under evaluation (FPSS-UE) based on the hierarchical data structure by at least: recursively traversing the nodes of the hierarchical data structure starting at the root node; at a particular node within the traversal, determining a first solid angle, measured with respect to a position associated with the particular node, between a position associated with the FPSS-UE and a position associated with a final pass shading sample stored (FPSS-S) with the particular node for which a subsurface scattering contribution has been previously determined; determining a first threshold value in part by applying a luminosity function to an incident irradiance associated with the particular node; and depending on the determined first solid angle relative to the first threshold value, selectively either: (1) when the first solid angle is less than the first threshold value, adding the previously determined subsurface scattering contribution stored with the particular node to the total radiant exitance for the FPSS-U, or (2) when the first solid angle is greater than or equal to the first threshold value, estimating a newly determined subsurface scattering contribution corresponding to the particular node, storing the newly determined subsurface scattering contribution corresponding to the particular node in association with the hierarchical data structure, and adding the newly determined subsurface scattering contribution to the total radiant exitance for the FPSS-UE.