Raytraced Order Independent Transparency part 2

In the previous blog post I discussed how raytracing can be used to achieve order independent transparency (OIT) for some types of transparencies and how it compares to other OIT methods like per pixel linked lists and Multi-layer Alpha blending (MLAB). The basic idea, since DXR doesn’t support distance sorted traversal of the BVH, was to use a closest hit shader to find the closest to the camera intersection and then use the position of the intersection as the origin of a new ray to trace through the BVH. That worked well in that it achieves OIT but the fact that each ray has to traverse the TLAS from the top every time we find an intersection is not ideal.

Raytraced Order Independent Transparency

About a year ago I reviewed a number of Order Independent Transparency (OIT) techniques (part 1, part 2, part 3), each achieving a difference combination of performance, quality and memory requirements. None of them fully solved OIT though and I ended the series wondering what raytraced transparency would look like. Recently I added (some) DXR support to the toy engine and I was curious to see how it would work, so I did a quick implementation.