I believe you’re referring to 2 separate GI methods from NVidia powered by RT cores. It’s confusing because NVidia calls everything RTX, when that’s the hardware/brand name, and they purposefully change names to resemble RTX(i.e. see the Square Enix path traced demo being referred to ray tracing with RTX… two separate things and fully path traced images are way more impressive, but there’s no “PTX” to market right now) Btw did you get to work on that?
RTXGI is the standard method of sending rays to the scene with x samples per pixel
DDGI is another method that uses raytracing on top of previous methods of Spherical Harmonics/probes to improve visibility/light leaking, dynamic updates, etc
I actually double checked on this and NVidia’s main page changes Morgan’s writeup from DDGI to RTXGI:
NVidia: https://devblogs.nvidia.com/rtx-global-illumination-part-i/
Morgan McGuire’s site: https://morgan3d.github.io/articles/2019-04-01-ddgi/index.html