Isosurfaces for whole segments

[fm3]

URL of deployed dev instance (used for testing):

• https://isosurfaceneighbors.webknossos.xyz

Steps to test:

• open a dataset with a segmentation in "view mode"
• enable isosurface rendering in the dataset settings
• shift click on a segment to initiate the isosurface rendering
• ideally, click on a segment which is relatively large so that its computation is split into chunks (parts should appear sequentially)

Issues:

• fixes Request isosurface for entire segment #3647
• fixes Hybrid tracing: Skeletons are created while brushing #3688

---

• Updated changelog
• [ ] Updated migration guide if applicable
• [ ] Updated documentation if applicable
• Needs datastore update after deployment
• Ready for review

[fm3]

@philippotto the back-end sends a NEIGHBORS header similar to MISSING-BUCKETS. It contains a list of numbers, e.g. [0,2,5].
This is the order of the six surfaces (x,y,z being the width height and depth of the requested block):

      val front_xy = BoundingBox(Point3D(0,0,0), x, y, 1)
      val front_xz = BoundingBox(Point3D(0,0,0), 1, y, z)
      val front_yz = BoundingBox(Point3D(0,0,0), x, 1, z)
      val back_xy  = BoundingBox(Point3D(0,0,z), x, y, 1)
      val back_xz  = BoundingBox(Point3D(0,y,0), 1, y, z)
      val back_yz  = BoundingBox(Point3D(x,0,0), x, 1, z)

Feel free to request changes on how the back-end behaves :)

Edit 2021: There was a bug in this surface list that was later fixed in this commit

[daniel-wer]

Awesome, couldn't generate large segments as the datasets on dev are not segmented globally, but the loading of neighboring cubes definitely works :)

@fm3 One thing I noticed, for 16-bit segmentations the backend doesn't return any vertices. Should not block this PR as there are other problems with 16-bit segmentations anyway (mapping support), but I just wanted you to be aware of it.

[daniel-wer]

Oh 😁 Nice!