Building Blender requires dependencies nvidia-cuda-toolkit and dev-cpp/eigen. However eigen needs nvidia-cuda-toolkit built before it can be built but the package tries to build eigen first causing it to fail.. --skipfirst and -exclude will only allow to build the rest of the packages to which point the build will fail with dev-python/numpy version being the issue if using ~amd64 arch. The only version of numpy that was able to successfully build is numpy-1.10.4. I was able to build blender by masking the other versions of numpy and added "media-gfx/nvidia-cuda-toolkit" right to DEPEND= section of the ebuild to see if it would cause it to build the toolkit first. Mine then built it in the correct order, but this was after doing --skipfirst so not sure if that finally got it to build in the right order or not.
I don't think this can be reproduced with the current package versions. I can build blender 2.79b-r1, nvidia-cuda-toolkit 10.1.105-r1 and eigen 3.3.7 on amd64 with cuda enabled. I am using stable numpy 1.14.5 Looking at the ebuilds, blender always depends on eigen. Both blender and eigen depend on nvidia-cuda-toolkit when they have cuda enabled. With cuda enabled for both blender and eigen, portage builds nvidia-cuda-toolkit before eigen, and then builds blender. All compile and work correctly on my machine. The ebuild does not require eigen to be built with cuda when blender is built with cuda. It can be difficult to ensure that cuda is enabled for all packages under amd64 as it requires both cuda use flag enabled, and the amd64 keyword (as cuda is masked for stable packages under the amd64 profile). This is the only way I can think force eigen to emerge before nvidia-cuda-toolkit. The packages build in parallel and eigen does finish building before nvidia-cuda-toolkit but they both compile successfully. I wondered whether blender with cuda would fail to build when eigen is built with cuda disabled, but all packages including blender build correctly in this scenario and cycles finds and uses my graphics card. So there is no need to have blender depend on eigen[cuda?] As blender 2.78 is no longer in the tree for testing, I think we should close this bug
Please test with the latest version and report, if there are still problems.
