RDNA 2 hardware raytracing

Reading through the recently released RDNA 2 Instruction Set Architecture Reference Guide I came across some interesting information about raytracing support for the new GPU architecture. Disclaimer, the document is a little light on specifics so some of the following are extrapolations and may not be accurate.

According to the diagram released of the new RDNA 2 Workgroup Processor (WGP), a new hardware unit, the Ray Accelerator, has been added to implement ray/box and ray/triangle intersection in hardware.

To z-prepass or not to z-prepass

Inspired by an interesting discussion on Twitter about its use in games, I put together some thoughts on the z-prepass and its use in the rendering pipeline.

To begin with, what is a z-prepass (zed-prepass, as we call it in the UK): in its most basic form it is a rendering pass in which we render large, opaque meshes (a partial z-prepass) or all the opaque meshes (a full z-prepass) in the scene using a vertex shader only, with no pixel shaders or rendertargets bound, to populate the depth buffer (aka z-buffer).