Do meshes need to be closed?

kmyung

Hello there, a quick question for all.

I've been doing re-topology and was wondering if the meshes need to be closed in areas where you wont see the topology? example: the head+neck is done with re-topology but has a hole in the bottom of the neck. Do i need to close the mesh or can I leave it open to save some polygons? Thank you!

Brian "Panda" Choi

You can leave it open.

Just needs to look good, usually.

kanga

Yeah you can leave them open. Leaving open areas doesn't affect baking (that I know of). You only have to be careful when you are rigging that animation of the mesh doesn't reveal those holes, or empty areas. When you are modeling its a good idea to run a mesh check on each part to  make sure the surfaces  are connected, and there are no common errors like internal polys and the like. For game models its also important to have intersecting meshes at an angle to each other. Two or more overlapping tris occupying the same space and orientation produce a shimmer effect which isn't too pretty.

musashidan

kmyung said:

 Do i need to close the mesh or can I leave it open to save some polygons? Thank you!

You might think that you're saving polygons but the amount of vertices(which is what really matter in an engine) is the same, or even more sometimes. Smoothing/UV splits add to vert counts as well.

But leaving meshes open can certainly make modeling easier(and save unwrapping time/space) and of course faces that will never be seen should always be deleted - provided of course that it doesn't interfere with animation.

Alex_J

I've found that, when rigging and animating humans, sometimes it's easier to connect some parts even if they are hidden. Here's some pictures. Easier to see than explain : 


Originally, the chainmail arms were a separate mesh just inserted inside the torso. This made rigging more difficult though, as I had to get inside, lock the inside edge vertices down with 100% weight to a spine joint, and then do a lot of playing back and forth to get it so that they don't pull out from torso with arms overhead nor poke out with the arms come forward and down. 

In the end, it was way easier to to just make it a contiguous mesh. Then it's just a matter of blending the weights to get the smoothest deformation, but there's no trouble of seams breaking, etc. 

Of course, the head just plops into place there and is empty at the bottom. No need to to connect or close off anything there. 

TL:DR -- just a case by case basis thing. I'd start with things water-tight if you aren't sure, as you can always delete things out but sometimes, late in the process, adding more in can be troublesome.

musashidan

BIGTIMEMASTER said:

Originally, the chainmail arms were a separate mesh just inserted inside the torso.

Well that certainly wouldn't have made any sense for a number of reasons.

kmyung

^ may i ask why? is it wrong to separate the arms from the chest in terms of meshes?

Also thank you very much for everyone's replies.

musashidan

kmyung said:

^ may i ask why? is it wrong to separate the arms from the chest in terms of meshes?

Well, there's no reason to. You aren't gaining any advantage by doing it. It's easier to rig as a contiguous mesh plus it will cause issues with deformation. The question is rather: why would you want to do it as opposed to why not?

poopipe

It'd make it easier to minimise deformation issues as the arms rotate forward and backwards - sleeveless torso coverings are a godsend if you aren't allowed twist bones in your rigs

Alex_J

The reason I did it initially and on some other models was to save time and effort not bothering to reroute edge loops when different parts of a model have different density, or in some cases the torso part does a fine job of covering the sleeve and this makes rigging easier. Also, like poopipe mentioned, if the torso is a rigid thing, like armor, and the sleeve is separate, then I can rotate it without any deformation at all (or minimal anyway). 

I'm very new to rigging, so not everything I do makes sense. I just make it up as I go along.