GI Boost

Overview

GI Boost is an optimization which drastically improves the performance of global illumination.

The optimization is simple: Disable GI calculation on any pixel if that pixel is in sunlight.

Thanks to the modularity of the shading functions, our GI boost implementation takes up only 4 lines. These lines can be broken up as follows:

1. The first 2 lines calculate the 2 primary direct sunlight shading factors
2. The third line creates a GI brightness coefficient by multiplying the shading factors together, and then takes the complement. This creates a variable which smoothly interpolates between 0.0 (when the pixel is in sunlight) to 1.0 (when the pixel is in shade).
3. The final line exits the GI function if the coefficient is too small

GI Boost causes no reasonably perceptible image difference in most situations. This is because sunlight is generally so much brighter than GI that the linear composition of the 2 light sources renders GI almost completely invisible.

Pictures

Without GI Boost:

With GI Boost:

Exception mask: