Holes not preserved when splitting dynamesh. Answered.

[Run]

I’m not sure if this is a dynamesh limitation, a bug, or problem with my system
And before I submit a bug I was wondering if others could test this to see if it happens on their systems too.

Win7 64 bit 12GB RAM, NVidia 280M 258.96 notebook drivers

Steps to recreate

-Create a dynamesh object, something basic like a sphere or a cube is fine.
-Select the insert cylinder brush & insert a cylinder while holding the alt key to add a cutting object.
-Stretch the inserted cylinder with transpose so that it extends all the way through the dynamesh
-Update the dynamesh & it should now have a cylindrical hole cut through it.
(Alternatively, instead cutting a hole in a dynamesh, you can create a shadow box object what has
hole built into it and make that a dynamesh)
-Select the slicecurve brush & slice a line bisecting the dynamesh perpendicular to the hole.
-Press Shift-f to view polygroups, the dynamesh should now have 2 polygroups defined by the slice
-Turn on the groups options for the dynamesh & update the dynamesh.

The the dynamesh should split in to 2 pieces based on it’s polygroups,
but now, on both pieces, the hole has been capped at the area where the split occurred.

As a workaround you can cut the hole after the dynamesh has been split into pieces,
but that’s kind of limiting and sort of defeats the whole “artistic freedom” thing that dynamesh represents.

Also I’ve found that the workaround can have other errors/issues when used with imported objects,
so it’s not a 100% fix.

-Jeff

[Spyndel]

A picture(s) is worth a thousand words.

Something I’ll note about the slice curve brush, though. It has some limitations for splitting meshes into clean pieces. It’s great for making straight cuts through a volume, but if you slice through at broken angles, or across curves or angled geometry, it really only splits the surface of the volume with clean crisp edges, but the interior is still soft, and does not conform to the angle of the slice curve cut. The dynameshing process will sometimes not remesh these as expected, and you’ll get results sort of like cutting through a piece of candy with a hard crunchy shell, but a gooey interior.

In those situations, it is better to “cut” your mesh with other negative geometry, not the slice curve.

[gabo1991]

Hello Jeff

What you are encountering is a normal behavior. When you have the Group button for DynaMesh and then use the SliceCurve brush to create the new polygroups ZBrush will automatically use the Close Hole algorythim to make sure the surface has a water tight surface.

Even though you are using the cylinder to create the hole you are also splitting the sphere in half which creates a bigger hole then the one with the cylinder. You can see in the image that I have attached what I am referring to. Because you are splitting the sphere in half ZBrush will need to fill that larger hole.

You could just use the cylinder again to cut what I have left over.

Let me know if this helps.

[Run]

Ah, OK I understand. Thanks for the info,

-Jeff

[Totyo]

This is in fact a limitation: the DynaMesh is using the Close Hole function found in the Tool >> Geometry subpalette, but this function is designed to fill any kind of holes… but what you are showing isn’t a simple hole, it is a bridge to do between two opening.

In your example, the solution is to do the steps in another order: slicing the sphere, then doing the hole. By the way, this is a simple scenario and may not work in other scenarios.