Blender upstream added support (in 2.90) for using Intel's Embree ray-tracing library to improve rendering performance. There is currently no way to enable this in Gentoo. Intel's Embree is not available as an ebuild in gentoo yet, so that would need to be tackled first. Then, we can add it as an optional dependency behind a USE flag. Reproducible: Always
If this goes forward, given media-libs/embree exists in ::waebbl's overlay maybe would be interested in bringing it to ::gentoo, CC'ing in case.
The blender maintainer also has embree in it's overlay and was experimenting with it. Maybe, he's still waiting for an usd ebuild, which I promised to look at, but haven't had the time yet to get more into it. The embree ebuild in my overlay is slightly newer (3.12.2) than Adrian's one (3.12.1) but the current version is based on his ebuild. Maybe we should ping him too and ask about his opinion. I guess, we could use either of the two ebuilds. There were some issues with using embree, as blender was requiring a very specific combination of flags for embree and also a static library. But this was with early or beta 2.90 releases, however, I don't know what's current state of this.
I have been testing embree with blender and you can use https://github.com/redchillipadi/ebuild-overlay/blob/master/media-gfx/blender/blender-2.91.0.ebuild from my repository along with my embree ebuild if you want to try it out. It seems to work for me, but there are a two things I want to check before submitting it. To enable embree with blender, it must be compiled with tbb,static-libs,raymask,-ispc,-tutorial as given by blender's install-deps --show-deps command. I am not entirely sure that excluding tutorial is necessary but enabling ispc certainly breaks it. Embree upstream also allows specification of the SSE, AVX, AVX2, and AVX-512 instruction sets to build against, rather than the default to build for all of them, and I would like to get this to be taken automatically from cpuflags. However when I added use flags to limit the instruction sets the build fails to work. I think blender links just against AVX2, but I haven't been able to get it working when I only build with this instruction set. Once I have sorted these out, I will update and submit the latest version. As my ebuild was originally from Bernd, I suspect recombining our implementations will not be too difficult. However at the moment I am prioritising adding support for blender and other graphics libraries in Gentoo to build against the exact GPU architecture required to add support for the latest graphics card features, and also allow CUDA to support older GPUs
Fixed already in https://github.com/gentoo/gentoo/pull/20565. See the work in: bug 795003 bug 778008 bug 774372 bug 673422 bug 737388
