Hull operation

[MethylBromide]

Under the category of "Combine", it would be very helpful to have a "convex hull" operation that takes the selected items and creates the minimal solid that encloses all of them, as if they had been shrink-wrapped. I understand the manifold library does support calculating this shape, so it shouldn't be a huge deal to add. I use this feature frequently in other programs, where it's invaluable in creating objects of the more free-form than mechanical style. It's also a big help for minimizing overhangs and surface discontinuities that result from trying to align different shapes so their facets are the same size (e.g. a half-sphere sitting on top of a cylinder).

Making this a "modify" operation that creates the new shape as a mesh, failing to preserve the original objects, would be an acceptable alternative, though not as desirable. (One could always duplicate the objects and keep the copies grouped with the hulled object, for future editing).

This has been brought up in discussion but not really explored -- just refused.

[henmedia]

@MethylBromide thank you for writing it up so clearly, and you are right that it was turned down before without a proper look. Your examples convinced me, and it is built for the next version.

Hull is a new tool under Combine. Select two shapes or more and click it: they are wrapped in their convex hull, the smallest body without dents round all of them. A half sphere on a cylinder becomes a dome with no step, four cylinders at the corners become a box with round corners, two spheres a capsule. Holes in the selection are cut out of the hull afterwards.

It is the version you preferred: the originals are kept. The hull is a group of its own kind, so Edit group opens it, you move, resize or swap a part, and Done wraps it anew; Ungroup gives the parts back. The hull itself is a mesh, so round parts show their facets, like an imported STL. For AI clients there is layerling_hull_objects as well.

@rondlh you asked for this in #329 too, so it should help with the four corner posts you described.

[henmedia]

@MethylBromide @rondlh the Hull tool is out in 1.110.0, under Combine.

[MartinShake]

I have been playing with this over the weekend. It has some really interesting possibilities. I 3D print musical instruments, so trying to merge geometric shapes into something that looks more organic is useful. I was wondering if there could be some sort of slider that increases or decreases the amount of merge. In effect soften the fillets. At the moment it seems all or nothing.

Martin

[rondlh]

I have been playing with this over the weekend. It has some really interesting possibilities. I 3D print musical instruments, so trying to merge geometric shapes into something that looks more organic is useful. I was wondering if there could be some sort of slider that increases or decreases the amount of merge. In effect soften the fillets. At the moment it seems all or nothing.

Martin

Hi Martin,

Currently the Hull operation has a quite serious bug: #329
The hull operation is a operation that is executed by the underlying mesh library (Manifold 3D), so I do not think much is possible in terms of sliders. What you probably need are some sculpting tools that allow you to push and pull the surface like clay.

[henmedia]

@MartinShake thank you for trying it, and musical instruments are a good use. The hull has no amount to set: it is the one convex body round everything you select, so there is nothing to soften between "merged" and "not merged", as @rondlh says. For softer blends, a loft between two outlines (it can be tilted or twisted, and one end can be smaller) often does what you describe, and so does hulling just two or three parts that belong together instead of the whole selection. layerling has no sculpting tool that pushes and pulls the surface like clay.