NVIDIA has posted the first part of a two-part technical deep dive written by Morgan McGuire, Adam Marrs, and Alexander Majercik that discusses Dynamic Diffuse Global Illumination, introducing DDGI and reviewing global illumination. DDGI creates realistic rendering for games by computing diffuse lighting with ray tracing, allowing developers to extend their existing light probe tools, knowledge, and experience with ray tracing to eliminate bake times and avoid light leaking. Now that hardware-accelerated programmable ray tracing is accessible for developers (DXR, VulkanRT, OptiX, Unreal, Unity), global illumination can be computed in many ways with DDGI as another strategy to expand developers' options.
NVIDIA highlights the advantages and potential costs of DDGI and provides more definition of global illumination. For example:
Direct illumination is the light arriving at a surface straight from the emitter. I’ve drawn the path of two direct illumination light rays as bright white arrows. There are an infinite number of other direct illumination rays.
When the direct illumination scatters off surfaces into the camera, it can see those surfaces. The color that we see for a surface is the color of light that the surface reflected. This is represented by the gray arrow for the gray sphere and a yellow arrow for the yellow wall. We call these surfaces that the camera sees from its viewpoint the “[camera] primary surfaces”. Note that any surface that receives direct illumination is a primary surface from the light’s viewpoint.
There are also secondary surfaces that the camera can’t see directly, but that affect the image...That light is indirect, or global illumination, abbreviated as “GI”.
Check out the full article here.