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.

The implementation was really simple. Since there is no mechanism to sort the nodes of a BLAS/TLAS based on distance from the camera, the ray generation shader keeps tracing rays using the result of the closest hit shader as the origin for the next ray until there is nothing else to hit.