Feature: 3D renderer support

[andreped]

Currently, it is possible to render the MRI with segmentation overlay in all 2D orthogonal planes.
However, there are numerous scenarios where visualising segmentation structures in 3D would be beneficial.
Having 3D rendering support would therefore be of interest, but finding a solution that works across all operating systems (without OpenGL due to macOS) might be a challenge.

[andreped]

Perhaps we should replace the current 2D viewers with pyFAST, which also has great support for 3D rendering surface models, which it also can generate.

Here is an example of how to extract the surface model and render it in 3D.