Tutorial: Creating a Polymesh Z
From ZBrush Info
In this section we’ll use the Create Difference Mesh feature to quickly create a custom 3D shape, then modify the subdivision smoothing via ZBrush 2’s Crease feature.
Contents |
Creating the Z
ZBrush 2 has the ability to create a 3D mesh by comparing a model’s current state to its stored morph target. We’ll put that to work here by creating a 3D letter “Z” from a Circle3D primitive. Along the way, we’ll also make use of ZBrush’s mesh visibility features.
Create a Polymesh Circle
- Begin by selecting the Circle3D primitive.
- Press the Tool:Make Polymesh button.
Since the Difference Mesh feature uses a stored morph target, and only polymesh objects can store one, we need to convert the primitive into a polymesh.
- Select the new polymesh and draw it on the canvas.
- Enter Edit mode and activate the Polyframe view.
We’ll need to be able to see the polygons in order to selectively hide some of them.
Create the Z Shape
- Using a red drag-rectangle, hide several polygons. (See Hiding and Showing Model Parts.)
- Continue to hide polygons, creating a simple “Z” shape.
As you work, you will find that sometimes it’s beneficial to use polygon selection and other times it’s easier to use points. If you want to use points, the fastest approach is generally to just make sure that your selection box doesn’t fully enclose a polygon.
- Press Tool:Geometry:Delete Hidden
We no longer need the hidden polygons, so we’ll delete them.
Create the Z Polymesh
- Press Tool:Morph Target:StoreMT
This stores the current geometry so that it can be referenced later.
- In the Tool:Deformations menu, set Offset to Z and then enter a value of around -40.
This moves all of the visible points toward the camera by 40% of a ZBrush unit, or 2/5 the size of the object.
- Back in the Morph Target menu, press CreateDiff.
At this point, ZBrush compares the current mesh to the stored morph target and creates a brand new mesh.
Smooth and Crease the Z
Draw the New Mesh on the Canvas
- Exit Edit mode and clear the canvas.
- Select the MorphDiff_PM3D_Circle3D tool.
ZBrush automatically names models in a way that makes it easy to tell how they were derived. From the name alone, we can tell that it’s a difference mesh generated from a polymesh3D object that was in turn derived from a Circle3D primitive. Of course, you can rename the model to anything you’d like by saving it.
- Draw the new model on the canvas and enter Edit mode.
As you can see, the new model is a fully-enclosed 3D figure. ZBrush used the stored morph target as one group, the offset position as a second group, and the polygons filling the difference between the two as a third group. This technique can be used in a remarkable variety of ways. For example, form-fitting clothing for a figure could be created very quickly and easily.
Subdivide the Z
Now let’s take a look at what happens when the mesh is divided a few times.
- Press Tool:Geometry:Divide three times.
By default, when the mesh is divided it is also smoothed by averaging the new points with the pre-existing points. This behaviour can be overridden by turning off Tool:Geometry:Smt but the result would be that the mesh remains very faceted. What if you want partial smoothing instead? ZBrush 2 provides a way.
Add Edge Creasing
- Press Ctrl+Z three times to return to the original mesh.
- Rotate the model to the side, activate Pt Sel, and draw a red rectangle to hide all but the front of the model.
- Press Tool:Geometry:Crease.
The polyframe view will change to show a fine dotted line around the edges of the visible area.
- Restore full visibility by holding Ctrl+Shift and clicking on any blank part of the canvas.
- Divide the mesh three times again.
This time, the front surface of the mesh remains flat. The crease tags serve as weighting to prevent their adjacent edges being smoothed when the geometry is divided.
When you look closely at the polyframe, you will see that the hidden polygons remain uncreased. So the edges where the front and side groups come together are only creased along one side. Let’s crease the other side, as well.
- Press Ctrl+Z to undo the mesh subdivision.
- With Pt Sel off, rotate to the side view and use red drag-rectangles to hide the front and back surfaces.
- Press Crease.
- Restore full visibility.
Now you will see that the edges common to the front and side surfaces have two rows of dotted lines.
- Divide the mesh three times again.
The edge is now sharper than ever, but the mesh does not have a faceted appearance. This is because the non-creased edges are still being smoothed. Creases are very useful for creating mechanical objects!
Changing Crease Sharpness
- Undo several times until only the front surface is creased.
- Restore full visibility.
- Set Tool:Geometry:CreaseLvl to 1.
- Divide four times.
The crease level tells ZBrush the maximum level at which to apply the crease tags. With a value of 1, the crease is only applied the first time the mesh is divided. For each subdivision after that, the crease is ignored and the mesh is smoothed. The result is a front edge that is slightly harder than the back edge.
- Undo the division and set the CreaseLvl to 2.
- Divide the mesh four times.
Now the crease is used for the first two subdivisions, and ignored for the second two. The result is an edge that’s harder than the back surface, but still somewhat soft.
In Conclusion
In this chapter, we’ve taken a look at how ZBrush 2’s mesh visibility controls operate and can be used to interact with the mesh. We’ve also used morph targets to store a base level for a mesh that was then modified. By comparing this modified mesh to the stored morph target, ZBrush was able to quickly create a shape that would have been very difficult to model by other means. Finally, we’ve examined how creases can be used to modify how ZBrush subdivides a mesh, giving you control over the sharpness of your model’s edges. A tutorial on this subject is also available in ZScript format in the Help system. Go to Modeling 3D Objects/Creases to view it.
