ZBrush has so many great features that it's easy to overlook one of the most useful aspects of ZBrush - Polygroups. Polygroups are really just a way of assigning groups of polygon faces to a selection. These polygon groups are distinguished from one another by their colors, viewed by enabling PolyFrame. You can create a Polygroup by hiding other polygons and grouping the visible polys. Or you can mask out an area and group those polygons. Check out the Polygroups subpalette of the Tool palette for more creation options.
So once you've created some polygroups, what can you do with them? Let's take a look at five ways you can use Polygroups to enhance your ZBrush workflow.
Extrude Polygroups using Transpose
The Transpose tool isn't just for moving objects around your ZBrush canvas. In combination with Polygroups, you can use Transpose to extrude faces in or out of your surface. Once your Polygroup is defined, activate Transpose from the Brush palette or just switch from Draw to Move (W). Now CTRL-click on the Polygroup. CTRL-drag on the center circle to extrude the Polygroup in or out from the surface. Holding shift will allow you to constrain the extrude along the normals of the surface. If you use Scale instead of Move, you can create an inset.
Control the Effect of Your Brushes
When working with really complex models, made up of lots of different pieces, sometimes it can be difficult to only affect certain parts with your strokes. For instance, you might want to use the Move Brush to vary individual instances of rocks or feathers that are within the same subtool, without affecting other nearby pieces. First you need to assign different Polygroups to each instance by choosing Autogroups from the Polygroups subpalette. This will create a new group for every separate piece, but you can also create custom groups on single piece of geometry. Now, after activating your brush, go to the Automasking section of the Brush palette. If you set Mask By Polygroups to 100, then your brushstrokes will only affect the first Polygroup that you click on. If you set it lower than 100, the strokes will mostly affect the first Polygroup touched, with a falloff occurring across any additional Polygroups.
Define UV Islands
UV Master can be a great way to quickly lay out some good UVs on your geometry. When using UV Master, however, you give up a little bit of control in how the UVs are created and distributed. By using Polygroups, you can get a little of that control back. Simply break your model into Polygroups based on your intended UV islands. You can use masking or make only your intended polygons visible and choose Group Visible from the Polygroups subpalette. Then, in the UV Master, turn on the Polygroups button. Now when you unwrap your UVs, all of your polygroups will be separated into different UV islands.
Polygroups can be a great help in sectioning off your models in order to create complex layered panels for things like bodysuits, uniforms or armor. Once you've assigned your Polygroups, you can use the Edge Loop tools to create the panels themselves. Found in the Tool palette, under Geometry/EdgeLoop, Group Loops will allow you to create a custom number of edge loops surrounding your Polygroups. These can be used to create trim or a more finished edge once extruded. You may also use Panel Loops to quickly create raised, beveled panels based on your Polygroups.
Polygroups will allow you to connect other pieces of geometry seamlessly into your model, without using DynaMesh. First define a Polygroup where you'd like your new geometry to connect. Mask out the appropriate area and hit CTRL + W to create a Polygroup from your mask. To create cleaner Polygroup edges from the mask, increase the polish amount next to Group Masked in the Polygroups subpalette. Now select an Insert Mesh brush with an open piece of geometry- try InsertHCylinder. Draw it out over your new polygroup and CTRL-drag in the canvas to unmask. CTRL-drag again to create a seamless connection between the two pieces. As a bonus, the new polygons that are created are assigned a new Polygroup.
These are just a few of the ways Polygroups can be used to enhance your ZBrush tools and let you use them to their full potential. How do you use Polygroups in your workflow?