Dissapearing objects

[Anonymous]

I have a menu of open objexts(eyes) but sometimes they will not appear at all when placed on a mesh.  There is just a crosshair there.  Other objects like the nose or ear come in horizontal.

Any ideas

[MagWeb]

If you say the open part disappears: Do you mean the part disappears at certain regions of the target mesh while it is visible dragging it to different positions?

If so: Open parts disappear if MM can't find a solution to merge the part to the target. (Critical issues are: The part wraps all around the target so it intersects itself, the target surface owns different mesh densities, the bending of the part would result in self intersections....)

The ear part in your screenshot is a solid part ( blue cube symbol) and I guess the nose in the scene was a solid part as well (for MM can't handle open parts with several not connected surfaces).

"Solid parts" can be not watertight as well. Dropping such a solid part MM doesn't merge it to the target surface but places its bounding boxes center (assuming zero Offset) at the target surface. The orientation of a solid part depends on the orientation at the moment you created that solid part. It's up-direction will be perpendicular to the target surface later on.

[Anonymous]

Concerning your first quiery the open part I am referring to, rather, does not appear when dragged to the face.  As if the scale were too small.

I can try increasing the density of the mesh where it is placed however I thought was an automated thing.

The problem with the open base of the eye is that it is very flat.  So you are saying that if the lids recede into the negative space where the open part meets the face it will mistake that mesh for nothing?

With the nose thing, I tried Union but it is messing up.  It was brought in rather large and at the wrong angle so I'll try to re introduce it to the library.  

[MagWeb]

What happens if you scale the part down (either by a numerical input in Size or dragging the arrow on the widget)?

Yes, MM tries to remesh the seam target-to-part automatically. But there are cases (e.g big differences of mesh density on the target surface) where it fails.

An open part may be "negative"(= a cavity) - that should not be an issue. But e.g. if the target is a cavity and the part is a "high" positive one, bending the part might result in self intersections of the part's surface...

Could you upload the geometry of such a failing open part to look at? ( The .obj from ../meshmixer/libraries/parts/user/SomeFolderThere(by default:MyParts)) 

BooleanUnion can work only if there's no open boundary crossing the intersection line A-to-B. So the union fails in case of the nose...

[Anonymous]

Talking about the objects that don't appear, no they wont scal numerically or if the arrow is dragged.  I'm getting some other strange anomolies which I have included as pics in this post. 

-An open part(eye) that I used seemed to have a flipped cavity but did not show through to the inside.

-An open part will not appear when placed but will create a cavity. 

-An open part with a cavity such as a mouth opposite the open part placement area will have a "geo-toungue stretching to the origin or a new head will not fully display when dragged until applied

-An geomentric object(ball) that has an open part on it will not allow another open part from the same category to be placed(mouths)

I noticed that with the parts(mouths in this case) that simply wont work, the lips seem thinner whereas fuller lips seem to work fine?

I'm attaching a head and thin and thick lips objs to this post.

https://drive.google.com/open?id=1NpPyr_SdSkF4JzuvQFXnNSjsZNcoBsR6.

[MagWeb]

Open parts support a single (internally closed) and manifold surface only. Also no non connected mesh particles (maybe even watertight) are supported. Such parts might result in holes, unexpected results or even crashes. The resulting behaviour changed with MM's versions (3.5 on macOS results in crashes on such open parts here)

Both mouth parts you attached above own an interior open boundary (one mouth also comes with non manifold issues) and self intersections (lower lip intersects upper lip at the interior boundary). This is why you get this weird behaviour. You need to repair mesh errors and inside open boundaries before converting a region to a MESHMIX part.

There are no such issues here at the eye or head part you posted.

[Anonymous]

I would say you were correct it's just that I tried the face with the
open mouth parts and the majority of them work perfectly. I was surprised
myself. I'm just wondering what the difference is, where the code is
allowing one part to work and another to fail basically.
I tried closing the mouth a little on one of the ones that fails but when
I did that I got mixed results sometimes missing geo and sometimes just
gizmo. So there has to be some way for this type of part to work as other
mouths are more widely open but perhaps "fuller"?

Anyways. also wanted to mention there is no scroll wheel on the parts menu
when the categories reaches the bottom of the window. Major fix!

[MagWeb]

Did some tests with a two-boundaries open part. My test part is a cylinder where I discarded the upper and lower plane surface.

Found:

1. Seems MM takes the the longer boundary (and if lengths are equal the one owning more vertices) as the boundary to be welded to the target surface ???

2. Dropping a two-boundaries open part on a target the first time might result in a "spike to somewhere" (the center of the  "first object's first bounding box" in most cases). You might not see it at all, but if you can't see the blue line at the interior boundary after accepting the tool: It is there.

This spike is the result of sucking all vertices on the second boundary to this point. This point is created at the moment you import the first object to the scene. It doesn't move along the object as one transforms it . Dropping a two-boundaries open part on a second object the second seam is sucked to that point (not to its own center) as well.

Pivot was created before moving bunny1

3. This "spike to somewhere" blocks dropping any further open part onto an object already owning such a spike within a MM session. This gives the gizmo-only situation. If you save the scene as a .mix and reload it you'll notice different actual looks of the spikes. After that you can drop open parts again (until a two boundary part results in a spike again)

4. Using Type=RotInvCoor instead of COILS seems to be more robust on a two-boundaries open part (but there happened spikes in some situations too):

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Yep, if you added too many categories there's way to scroll the list of categories. You might move some or all default categories from .../Documents/meshmixer/libraries/parts/default but do not delete the default folder...

Another option might be to drop the parts via a mmAPI script...