In Rise of the Tomb Raider, not all locations benefit from VXAO equally well, and the reason for that lies in the game’s art and lighting solution. The game has separate channels for ambient lighting and ambient occlusion, and how exactly they are used is determined by materials. The ambient occlusion channel is often applied on top of direct lighting as well, and because VXAO is not a local effect and tends to add occlusion to large surfaces, some lights become dimmer. So we had to apply VXAO to the ambient light channel instead and keep HBAO+ in the ambient occlusion channel in order to achieve the best look.
It became clear that VXAO is mostly a long-range effect, and it’s useful to combine it with some short-range SSAO technique to highlight small features which cannot be adequately represented by voxels. For this reason, VXAO now includes an optional screen-space occlusion pass so that you don’t have to work with a separate SSAO library.