Game and movie studios are switching to physically based rendering en masse, but physically accurate filter convolution is
difficult to do quickly enough to update reflection probes in real-time. Cubemap filtering has also become a bottleneck in the
content processing pipeline. We have developed a two-pass filtering algorithm that is specialized for isotropic reflection kernels,
is several times faster than existing algorithms, and produces superior results. The first pass uses a quadratic b-spline recurrence
that is modified for cubemaps. The second pass uses lookup tables to determine optimal sampling in terms of placement, mipmap
level, and coefficients. Filtering a full 1282 cubemap on an NVIDIA GeForce GTX 980 takes between 160 μs and 730 μs with
our method, depending on the desired quality.